Synthesis and tautomerism of aryl - Core

6 downloads 0 Views 4MB Size Report
141 via reactions of 2-thiouracil derivatives 136 (R0 = H) with. N-aryl arylazomethanehydrazonoyl chlorides 1O in chloro- form in the presence of triethylamine at ...
Journal of Advanced Research (2010) 1, 255–290

Cairo University

Journal of Advanced Research

REVIEW

Synthesis and tautomerism of aryl- and hetaryl-azo derivatives of bi- and tri-heterocycles Ahmad S. Shawali Department of Chemistry, Faculty of Science, University of Cairo, Giza, Egypt Received 29 September 2009; revised 25 November 2009; accepted 2 March 2010 Available online 16 September 2010

KEYWORDS Heterocycles; Azodyes; Azocoupling; Tautomerism; Hydrazonoyl halides

Abstract This review summarizes results from the literature concerning synthesis and azo-hydrazone tautomerism of arylazo- and hetarylazo-derivatives of various bi- and tri-heterocycles reported by us and other research groups from 1981 to mid 2009. ª 2010 Cairo University. Production and hosting by Elsevier B.V. All rights reserved.

Introduction Aryl- and hetaryl-azo colouring matters have been in use since prehistoric times [1]. The interest in such colouring materials is due to the fact that many derivatives were found useful in the fields of material sciences and theoretical chemistry [2]. For example, many such azo dyes have been extensively used as dyes in various fields such as dyeing of textile fibers, coloured plastics, biological-medical studies and advanced applications in organic synthesis [3]. Recently, applications of such colouring materials to high technology have been attracting much attention. Dyes are used in various fields such as printing, electronic photography, colour formers, liquid crystal displays, E-mail address: [email protected] 2090-1232 ª 2010 Cairo University. Production and hosting by Elsevier B.V. All rights reserved. Peer review under responsibility of Cairo University. doi:10.1016/j.jare.2010.07.002

Production and hosting by Elsevier

laser technology, data storage and solar energy conversion [4]. Also, some of such dyes have found use as non-linear optical (NLO) materials. Such compounds have potential use in optical communications, information processing, frequency doubling and integrated optics [5]. In recent years, arylazo derivatives of various heterocyclic systems have been the subject of intense research by organic chemists [6] and dye manufacturers [7]. It is worth mentioning that azo-hydrazone tautomerism is not only of importance to dyestuff manufacture but also to other areas of chemistry. Also, azo-hydrazone tautomers have different tinctorial strengths (and economics) and different properties, e.g. light fastness. The intention of this review is to focus mainly on publications dealing with the synthesis and azo-hydrazone tautomerism of arylazo derivatives of various bi- and tri-heterocycles that have appeared in Chemical Abstracts during the period 1981–2008. Literature prior to 1981 will not be included unless it is felt essential to use the relevant information to put the problem into a common perspective. Emphasis is only given to the latest developments in the area. In this literature survey, the arylazo-heterocycles are reported in order of the increase of (i) the number of rings, (ii) the size of such rings and (iii) the number of heteroatoms

256

A.S. Shawali

present. The sequence of heteroatoms followed is: nitrogen, oxygen, sulfur, selenium and other elements if there are any. The site of fusion in fused heterocycles is indicated by numbers and letters and the numbering of the heterocyclic ring systems is that reported by chemical abstracts. Arylazo dyes of bi-heterocycles Arylazo derivatives of 5,5-biheterocycles 1H-Imidazo[1,2-b]pyrazoles Shawali et al. [8,9] reported that 5-amino-3-phenyl-pyrazole 2 reacted readily with 2-oxohydrazonoyl halides 1A–D in ethanol and yielded the respective 3-arylazo-2-substituted-1H-imidazo[1,2-b]pyrazoles 3 (Scheme 1). The spectral data of the latter were reported to be consistent with the depicted arylazo tautomeric structure [9]. Latterly other authors applied the same reaction for synthesis of other derivatives of 3-arylazo derivatives of 1H-imidazo[1,2-b]pyrazole 3 using other hydrazonoyl bromides as precursors [10–15]. Similar reaction of N-aryl 2-oxo-2-phenylethanehydrazonoyl bromides 1B with 3-methyl-5-aminopyrazole 4 was reported, however, to give a mixture of 5 and 6 [16] (Scheme 3). Treatment of 5 with acid resulted in the elimination of water to give the respective 1H-3-arylazoimidazo[1,2-b]pyrazole derivative 7 (Scheme 2) [16]. The product 6 was recovered unchanged upon similar treatment with acid.

Also, it has been reported that ethyl N-arylhydrazonochloroacetate 1E reacted with 3-phenyl-5-aminopyrazole 2 to give a product to which structure 8 was assigned (Scheme 3) [8,9]. The isomeric structure 9 was discarded on the basis that the isolated product was recovered unchanged after being subjected to oxidation treatment. Structures of type 9 are expected to be oxidized by analogy with 1-methyl-3-phenylhydrazono1,4-dihydroquinoxalin-2-one 10 which was reported to give 3-phenylazoquinoxaline derivative 11 upon oxidation (Scheme 4) [17–19]. Contrary to the foregoing reports, it was indicated that reaction of 3-phenyl-5-aminopyrazole 2 with each of the hydrazonoyl chlorides 1A, B, C, D yielded the respective 3substituted-1-aryl-4-phenyl-1H,6H-pyrazolo[3,4-c]pyrazoles 13 instead of the expected arylazo imidazopyrazole 130 or its isomeric arylazo pyrrolopyrazole 1300 (Scheme 5) [20,21]. Such Ph

Ph EtOCOC(Cl)=NNHAr + N N 1E 2 H

NH2

N

- HCl, - EtOH

H

N

N

ArNHN

O

Ph

8 N

H

N

N

NNHAr

O 9

Scheme 3 Ph RCOC(X)=NNHAr +

Ph N

1A-D

N

NH2

N H

2

Ar

N

N

H

N

N

H N

R

3

; D,

N=NPh

N

[O]

N O Me

N O Me

S R : A, Me; B, C 6H5; C,

NNHPh

11

10 N

O

Scheme 4 Scheme 1 Ph

Me PhCOC(Br):NNHAr

+

1B

N 4

RCOC(Cl)=NNHAr 1A, E-G

N H

NH2

PhCO NH2 COPh

N

NH2

N NNHAr 6

Me

N H 13

N

N

+

Ar

N

N

N

-HCl

H

Ph

NNHAr N

N

- NH3

7

Scheme 2

NH2 12

Ph

Ph N

N

N

N=N-Ar N

R 13' ArNHN

N H

N H 13"

Ph

N

N H

Ar

5 H - H 2O

NH2

COR N

Me

ArNHN

N H

COR

Me N

N 2

Ph

N

+

R : A, Me; E, EtO; F, PhNH; G, O

Scheme 5

N-

R

Synthesis and tautomerism of heterocyclic azo compounds

257

Me CH3COC(Cl)=NNHPh +

Me

Ph N

1A

Ph N

-HCl, -H2 O

NH2

N H

Ar

14

N

N

N

H CH3

N 15

Scheme 6

finding needs further evidence to account for such a suggested pathway. The reaction between 2-oxopropanehydrazonoyl chloride 1A and 3-methyl-4-phenyl-5-aminopyrazole 14 led, as expected, to 1H-3-arylazo-imidazo[1,2-b]pyrazole derivative 15 (Scheme 6) [22]. Also, it was claimed that reaction of 5-amino-3,4-disubstituted pyrazoles 16 with N-phenyl 2-oxopropanehydrazonoyl chloride 1A afforded the amidrazone derivative 17 (Scheme 7) [22]. In another report [23], reactions of 5-amino-3-phenyl4-bromopyrazole 16 with the hydrazonoyl halides 1A and 1B were reported to yield the respective 2-phenylazoimidazo[1,2b]pyrazole derivative 18 which, upon treatment with sodium sulfide, was converted into 19 (Scheme 7) [24]. No rationalization, however, was offered. A similar contradiction was also reported, indicating that reaction of ethyl 3,5-diaminopyrazole-4-carboxylate 20 with R'

R" CH3COC(Cl)=NNHPh

RCOC(X):NNHPh 1A, B R'/R" = Ph / Br

Ph

N

1A

NH2

N H

NH2 N

R' N

N

R" N

18

PhNHN Ph

Na2S

COCH3

SH N

N

N

N

CH3

17 H

NH

O

NH2

N

O

N H 23

H N=N-Ph

R

CH3COC(Cl)=NNHPh 1A

+

16

Br N

2-oxopropanehydrazonoyl chloride 1A yielded the 2-phenylazo derivative 21 and not the expected 3-phenylazo derivative 22 (Scheme 8) [25]. The latter isomer is to be the expected product of such a reaction as the pyrazole N(1)H is more basic than the exocyclic 5-amino group and thus the structure of the product isolated from such reaction seems to need further investigation. Reaction of 3-amino-4,5-dihydropyrazol-5-one 23 with Nphenyl 2-oxopropanehydrazonoyl chloride 1A was reported to yield 3-phenylazo-2-methyl-5,6-dihydro-6-oxo-1H-imidazo[1,2-b]-pyrazole 25 via dehydrative cyclization of the initially formed amidrazone derivative 24 (Scheme 9) [22]. Recently, Shawali et al. [2] reported that when equimolar quantities of N-aryl 2-oxo-2-phenylethanehydrazonoyl bromide 1B (Ar = Ph) and each of the azo derivatives 27a–g were refluxed in ethanol in the presence of triethylamine, the respective 3,7-bis(arylazo)-2,6-diphenyl-1H-imidazo[1,2-b]pyrazoles 28 were formed. Similar reactions of 27 (Ar = Ph) with each of N-aryl 2-oxo-2-phenylethane-hydrazonoyl bromides 1Ba–h

PhNH

N

- H2 O

O

N H

NH2 N

PhCOC(Br):NNHAr

N H

COOEt + CH3COC(Cl)=NNHPh 1A NH

KCN

Ph

-KBr

O

Ph

N

N

N

H

N H

Ar N

NH2

22

N

N

H N=N-Ph

-HBr , - H 2O Ph

N

N

Ph Ar / Ar' : XC6H4 / C6H5 ; C H / XC H 6 5 6 4

N NH N N Ar' 29

g, 4-NO2; h, 4-EtOCO

Scheme 10

Ar

N N

N

N NH

N Ar

Ar' N

X : a, 4-MeO; b, 4-Me; c, H; d, 4-Cl; e, 3-Cl; f, 3-NO2;

21

Scheme 8

- H 2O

PhCOC(Br):NNHAr' 1E

N

COOEt

CH3

CH3

N

NH2NH2

CN

Ph N

NH2

N NHAr

26 N

Ph

2

COOEt N

O

Scheme 9

27

N

N H

25

24

1B

NH2

N

19

Scheme 7

20

N

N Ph

R'/R" : Ph / Br; Ph / CN; H2N / PhN=N-

H N

H3C

N=N-Ph

R R: A, Me; B, Ph

- HCl

Ph 28

258

A.S. Shawali

also yielded the respective bis-arylazo derivative 28 (Scheme 10). The other regioisomeric structures namely 2,7-bis(arylazo)-2,6-diphenyl-1H-imidazo[1,2-b]pyrazoles 29 were discarded on the basis that reaction of 5-amino-3-phenyl pyrazole with 2-oxohydrazonoyl halides was reported to afford in all cases examined the respective 3-arylazo-2,6-diaryl-1Himidazo[1,2-b]pyrazoles and not the isomeric 2-arylazo-3,6-diaryl-1H-imidazo[1,2-b]pyrazoles [2,8,9,16,22,26,27] Although, four possible tautomeric structures A–D can be written for each of the compounds 28 (Fig. 1), they were found to exist predominantly in the tautomeric form A on the basis of their electronic absorption spectra and correlations of their acid dissociation constants in both ground and excited states, pK and pK*, respectively, with Hammett equation. For example, their electronic absorption pattern in dioxane revealed in each case two characteristic intense absorption bands in the regions 600–400 and 350–290 nm, similar to that reported for the azo chromophore [28]. Also, the electronic spectra of 28 (Ar = Ar0 = C6H5), in solvents of different polarities showed little, if any, shift. This result indicates that the studied compounds exist in one tautomeric form, namely the bis(arylazo) form A (Fig. 1). Furthermore, the results of the correlations of their acid dissociation constants by Hammett equation together with the spectral data provided evidence that indicates that such compounds exist predominantly in the 1H-bis(arylazo) structure, namely the tautomeric form A in both ground and excited states (Fig. 1).

afforded the respective 6-arylazoimidazo[2,1-b]thiazoles 31 (Scheme 11) [29]. The other isomeric structure 32 was excluded for the isolated products on the basis that reaction of 2-aminothiazoles with a-halo ketones gives 5-substituted imidazo[2,1b]thiazoles [30] and alternate synthesis of 31 by coupling of diazonium salts with 3,5-diphenyl imidazo[2,1-b]thiazoles 33 (Scheme 11) [30]. In another report [31], it was indicated that reaction of other 2-amino-4-methylthiazole derivatives 34 with the 2oxohydrazonoyl halides 1A, B led to the formation of the respective 5-arylazoimidazo[2,1-b]thiazoles 35 (Scheme 12). The other expected regioisomers 36, however, were not formed. Reaction of 2-amino-4-phenylthiazole 30 with ethyl N-(arylhydrazono)chloroacetate 1B in the presence of triethylamine was reported to give one product that was assigned the structure 37 (Scheme 13) [9]. The other isomeric structure 38 was discarded and although the isolated products 37 can have two tautomeric forms (37 and 370 ), they were assigned the ketohydrazone tautomeric structure 37 on the basis that their IR spectra revealed CO and NH bands near 1710 and 3360 cm1, respectively. Similar reaction of 4-methyl-2-aminothiazole derivatives 34 with ethyl N-(arylhydrazono)chloroacetate 1B

Ph

Imidazo[2,1-b]thiazoles 6-Arylazoimidazo[2,1-b]thiazoles 31 were first synthesized by Shawali et al. [9] by reaction of the appropriate 2-aminothiazole derivatives with hydrazonoyl halides. Thus, reaction of 4-phenyl-2-aminothiazole 30 with 2-oxoalkanehydrazonoyl halides 1A, B, H were reported to give, in each case, a mixture of three products, namely the hydrohalide salt of the starting 2-aminothiazole, tetrazine derivative and 6-arylazo-3,5-disubstituted imidazo[2,1-b]thiazoles 31 [9]. However, when equivalent amounts of hydrazonoyl halide and 2-amino-4phenylthiazole 30 were refluxed in ethanol in the presence of triethylamine, only the respective azo-products 31 were obtained in 80% yields. Similar reaction of 2-heteroaryl-2oxohydrazonoyl bromides 1H with 2-amino-4-phenylthiazole Ar N Ph

H

N 7a

N

R

N N

S

N

N

4

3

Ph

2

N

Ar'

ArN2Cl Ph

NC

R

N

R : A, Me; B, Ph ; H,

N N C6H4Me-p

Ph

N

S 33

Me

N

N

RCOC(X)=NNHAr + 1A, B

H

R' - HX

NH2

S

- H 2O

34

Ar'

N Ph

N

C

R

N N

N

N

N

Ar

N

N

N

S

Ar

32

N

B

N

Ph

Ar

31

Ph

Ph N

Ar

N N

N

N

N

A

NH2 30

Ph

N

1 5

N

Ph

S

- H 2O

Scheme 11

N

6

N

H

- HX

Ar

7

N

RCOC(X)=NNHAr + 1A, B, H

N Ar'

Me

N H D

N N

R'

N Ar'

Fig. 1 Possible tautomeric structures for 3,7-bis(arylazo)-2,6diphenyl-1H-imidazo[1,2-b]pyrazoles.

R

N

Ph

Ph

S

N

N

Me N

Ar

R'

36 R : A, Me; B, Ph R' = H, Me, Ph

Scheme 12

N N

N N

S 35

R

Ar

Synthesis and tautomerism of heterocyclic azo compounds R EtOCOC(Cl)=NNHAr 1B

259 RCOC(X):NNHAr

N

+

1A, E, H

NH2

S

R'

N N H

-HX

- HCl,H2O

30: R / R' = Ph / H

H RCOC(Cl):NNHAr 1B, C

S

- HCl

44

34: R' = Me R R'

O

N

N

N

S

H N

R Ar

N

R'

N

S

37

N

Ar

N N H

45

H

47

O

N

R'

R

OH

N

N

N

S

N

R'

Ar

N=N-Ar

N

N

N

Ar

N

Ar

48 NC

38'

37'

N

S

N

46

OH

N

OH

S

N

S

- HR

R

38

NNHAr

S

H

- H2O

N

R

N

NNHAr

S

COR

N

COR

N

R : A, Me ; B, EtO; C, PhNH;E, Ph; H, Ph

R' = a, H; b, Me; c, Ph

N

N

C6H4 Me -

Scheme 13 Scheme 15 Ph RCOC(Cl):NNHAr 1B, C - HCl Ph Ph

N S H 39

40 R N

Ar

N

Ph

S

N

NNHAr

S

N H

- H2O N

N

COR

N

42 OH

Ph

1A, E

-HX

Ph

- RH Ph

1H-Pyrazolo[5,1-c][1,2,4]triazoles RCOC(X):NNHAr

Ph

NNHAr

S

N

H

COR

N

H

Ph

N

Ph

43

N

N

Ar

S

N

N-Phenyl benzenecarbohydrazonoyl chloride 1I reacted with 3-amino-4-(arylhydrazono)-pyrazolin-5-ones 49 in refluxing ethanol to yield the respective 7-arylazo-1H-pyrazolo[5,1c][1,2,4]triazoles 50 (Scheme 16) [35]. Similar reaction of N-phenyl benzenecarbohydrazonoyl chloride 1I with 3,5-diamino-4-phenylazopyrazole 51 was reported to yield 53 probably via elimination of ammonia from the intermediate amidrazone 52 (Scheme 17) [36,37]. However, reactions of the same diaminopyrazole 51 with 2-oxohydrazonoyl chlorides 1A and 1C were reported to give the respective amidrazones 54 (Scheme 17) [21,37]. No attempts to cyclize the latter, however, were reported.

41 R : A, Me; B, EtO; C, PhNH; E, Ph

Scheme 14

was reported by Shawali et al. [32] to yield, however, the other isomeric products 38 (Scheme 13) [31]. 2-Mercaptoimidazole 39 was reported to react with each of N-aryl 2-oxoalkanehydrazonoyl halides 1A, E in the presence of triethylamine to give the respective thiohydrazonate esters 40 [21,33,34]. Treatment of the latter with polyphosphoric acid resulted in their cyclization to afford 41 (Scheme 14) [33]. Similar reactions of 2-mercaptoimidazole 39 with either ethyl N-(arylhydrazono) chloroacetate 1B or N-(arylhydrazono)-chloroacetanilide 1C yielded one and the same product, namely 43. The intermediate thiohydrazonate esters 42 were not isolated (Scheme 14) [21,34]. However, in one report [21] such intermediates were said to be the end products. Reactions of 2-mercapto-4,5-dihydroimidazole 44 with each of N-aryl 2-oxoalkanehydrazonoyl halides 1A, E [23] and 1H [29] yielded the respective products 46 (Scheme 15). Similar reactions of the 2-mercapto-4,5-dihydroimidazole 44 with either ethyl N-arylhydrazonochloroacetate 1B or N-phenyl 2-oxo-2-phenylaminoethanehydrazonoyl chloride 1C afforded a single product, namely 48 (Scheme 15) [23].

Imidazo[1,2-b][1,2,4]triazoles Reaction of 3-amino-1,2,4-triazole 55 with 2-oxohydrazonoyl halides 1A, E in ethanol was first reported by Shawali et al. [9] to yield the respective 5-arylazo-imidazo[1,2-b][1,2,4]triazoles 56 (Scheme 18). Similar reaction of the same aminotriazole 55 with the other hydrazonoyl bromides 1G was latterly reported by others [15] to afford the respective 56. The other isomeric 6-arylazo derivatives 57 were not produced. Similar reaction of 3-amino-1,2,4-triazole 55 with ethyl Narylhydrazonochloroacetate 1B was reported by Shawali et al. [9] to give 58 (Scheme 19). The other two isomeric structures namely 59 and 60 were discarded [9]. Structure 60 was discarded on the basis that the product isolated was recovered unchanged upon treatment with oxidizing agents. PhC(Cl)=NNHPh +

Ph NH NH N Ph

NNHAr

49 N N H NNHAr

1I

N

NH2

- HCl

O

N N H

O

- NH 3

Ph N N

Ph 50

Scheme 16

N=N-Ar N H

O

260

A.S. Shawali NH2

RCOC(Cl)=NNHPh

N

PhC(Cl)=NNHPh

N

1A, C NH2

N=N-Ph NH2

N H

1I

51

N=N-Ph N=N-Ph

NH2 N

NH2

PhNHN

N

N

NH2

COR Ph

54 NH2 R : A, Me; C, PhNH

NNHPh 52

N=N-Ph

N

N

N N

Ph

Benzofurans

Ph

2-Arylazo-3-methyl benzofuran 68 were synthesized by reaction of 2-oxoalkanehydrazonoyl halides 1A with phenols in the presence of base catalyst such as triethylamine or ethoxide anion and cyclization of the resulting aryl hydrazonate esters 67 via treatment with polyphosphoric acid (Scheme 22) [38].

- NH 3

53

Scheme 17

N

N

N

RCOC(X)=NNHAr + NH2

55 N H

1A, E, G

N

N

tives 61. Addition of the latter to preheated polyphosphoric acid at 80 C yielded the corresponding 2-arylazoindoles 62 (Scheme 20) [38,39]. Similar treatment of the amidrazones 63 (R00 = H or Me), prepared from the hydrazonoyl chloride 1J and N-methylaniline, was reported to yield the isatin derivatives 65 and 66 (Scheme 21) [39,40]. The formation of the latter products was considered to result from atmospheric oxidation of the cyclized intermediates 64, followed, in the case of 66, by hydrolysis.

N

R"

NNHAr COR

N=N-Ar R N

R"

H

N

56

N=N-Ar

N N

N

O

R

N R'

NNHAr

R

- HO 2 R"

N R'

R: A, Me; E, Ph R' = H, Me R" = H, Me

N=N-Ar 62

H

57

Scheme 20

N

R : A, Me; E, Ph; G,

R" 61

PPA

R

N

+ RCOC(X):NNHAr NHR' - HX 1A, E

R"

NH2

N

R"

S

R"

Scheme 18

R" + NHMe

R"

Arylazo derivatives of 5,6-biheterocycles

O

H

Cl

NNHAr 1J

R"

Indoles

R"

H

N NNHAr Me 63 R"

OH H

PPA

Reaction of N-aryl 2-oxoalkanehydrazonoyl halides 1A, E each with aniline or N-methylaniline in ethanol in the presence of triethylamine afforded the respective amidrazone deriva-

O

[O]

O +

- HO 2 R"

N NNHAr Me 64 Me

R" 65

N NNHAr Me

O

N

R" = H, Me Ar = Ph

N

EtOCOC(Cl)=NNHAr + N H

1B N

N

NNHAr COOEt

N

NH2

66

55

NH2

ArNHN

N

EtOCO N

COOEt

N

N N

N 58

N

N N

H

N N

ArNHN

H O

59

Scheme 19

NNHAr N

N H NNHAr O

N O Me

Scheme 21

N N

N

Me

NH2

R

R

H + R

O

NNHAr 1A

R

N 60

Cl

NNHAr

N N

OH

Me

O

H

PPA - HO 2

R

O

Me

O

NNHAr

67

Me R

O

N=N-Ar

68

Scheme 22

R = H, Me

Synthesis and tautomerism of heterocyclic azo compounds R'

+ SH

261 R'

O

R

X

NNHAr

1A, E R / X : A, Me / Cl; E, Ph / Br

RCO

R S

R' = H

2

S

NNHAr

1

N=N-Ar

H

70

N

R' = H R = H, Me, Ph

69

+ S-Ph

Ph

3

S +

RCO

NH 1 2

R = Me, Ph

N 3

NH2

H

4

R

5

S-R N

R

PPA

- H 2O R'

O

N

+

S-Ph RCOCN +

H2N

71

72

Scheme 23

Benzothiophenes 2-Arylazo-3-substituted-benzothiophenes 70 were obtained from the reactions of thiophenol with 2-oxoalkanehydrazonoyl halides 1A, E in the presence of base catalyst and treatment of the resulting aryl thiohydrazonate esters 69 with polyphosphoric acid (Scheme 23) [38]. It is worth mentioning that treatment of some phenyl thiohydrazonate ester 69 (Ar = Ph, R = H) with PPA was reported to give the 3-(phenylthio) cinnolines 71 as the main product, with an 18% yield. On the other hand, similar treatment of the esters 69 (Ar = Ph, R = Me, Ph) afforded the respective products 71 (27–35% yield) together with 4-aminophenyl sulfide 72 (32–60% yield) and acylcyanide (Scheme 23) [39]. The formation of 72 was considered to result through a cyclodehydration path involving the aromatic ring of the hydrazone moiety. The mechanism suggested to account for the formation of 72 involves a rather unprecedented [3,5] rearrangement in which the sulfur atom is one of the termini, as depicted in Scheme 23 [39]. Pyrrolo[1,2-a]pyridines Reaction of N-aryl 2-pyridinecarbohydrazonoyl bromide 1K with dimethyl acetylene-dicarboxylate 73 was reported to afford a mixture of 1-arylazopyrrolo[1,2-a]pyridine 74 and the usual 1,3-dipolar cycloadduct 75 (Scheme 24) [41]. Imidazo[1,2-a]pyridines In 1983 Shawali et al. [9] reported that reactions of 2-oxohydrazonoyl halides 1A, E–G and 1L each with 2-aminopyridine 76 in ethanol under reflux gave the respective 3-arylazo-2substitutedimidazo[1,2-a]pyridine 78 (Scheme 25) [9]. The other regioisomeric products 80 were discarded on the basis that 2-aminopyridine 76 has been known to react with a-halo ketones to give 85 (Scheme 26) [8,9,13–15,42,43]. Furthermore, the assigned structure 78 was confirmed by the fact that coupling of 2-substitutedimidazo[1,2-a]pyridine 79 with N-nitrosoacetanilide or diazotized aniline in ethanol was found to yield a product identical in all respects with 78 (Ar = Ph) [9,14].

N

Et3 N

Br

MeOCO 73

N-N-Ar -

1K

N

+

MeOOC

COOMe

N

N=N-Ar

N

COOMe

+

N

NNHAr

COOMe

N

COOMe

Ar 75

74

Scheme 24

Ethyl N-(arylhydrazono)chloroacetates 1B reacted similarly with 2-aminopyridine 76 and afforded 82 which was shown to have the keto-hydrazone structure (Scheme 25) [9]. The other possible regioisomeric structure 83 was discarded on the basis that reactions of 2-aminopyridine 76 with a-halo-esters were reported to give 84 (Scheme 25) [9,17,18]. Similar reactions of 2-aminopyridine 76 with N-(pyrazol-5yl) 2-oxohydrazonoyl halides 1M, N in refluxing ethanol in the presence of triethylamine or piperidine were reported not to give the respective arylazo derivatives 87 [44,45]. They yielded instead pyrazolotriazoles 86 probably via cyclization of the nitrilimine intermediates (Scheme 27). In this case it seems that 2aminopyridine 76 acted as a base catalyst. Thieno[2,3-b]pyridines 5-Arylazothieno[2,3-b]pyridines 89 were obtained by reaction of phenacyl bromide with 3-arylazopyridine-6(1H)-thiones 88 (Scheme 28) [46]. 4,6-Dimethyl-2-arylhydrazonothieno[2,3-b]pyridin-3-ones 91 were prepared by coupling 4,6-dimethyl-thieno[2,3-b]pyridin-3-one 90 with diazotized anilines in ethanol in the presence of sodium acetate (Scheme 29) [47]. On the basis of their IR (vCO 1680, vNH 3350) and 1H NMR spectra (dNH 11.2– 13.2), such products were assigned the indicated ketohydrazone tautomeric structure 91.

262

A.S. Shawali EtOCOC(Cl):NNHAr

RCOC(X)=NNHA

1B - HCl

1A, E-G, L - HX

NH2

N 76

ArNHN

ArNHN O

O

81

Ar

N

N

R

N=N-Ar 80

O

N N Ar

R 78

O N N

NNHAr 83

N 82'

ArN 2Cl

N

N

N

N

N

N

N 82

Ar

77

- H 2O

N H N

NH R

N

NH OEt

N

N

N 79

OH

R : A, Me; E, XC6 H4 ; F,

R N ; L,

; G, O

S

Scheme 25

RCOCH2 X

Me

RCH(Cl)COOEt

Me

N NH2 76

Ar-N=N

CN

R N 85

R

R

N H

N

N

N

84

PhCOCH 2 Br

NH2

Ar-N=N

COPh S

N

R

S 88

89 R = Me; Ph

O

Scheme 28

Scheme 26

Pyrazolo[3,4-b]pyridines Hydrazinolysis of either 92 or 93, each in refluxing ethanol containing a catalytic amount of triethylamine, was reported to give 5-arylazo derivatives of 1H-pyrazolo[3,4-b]pyridine 94 (Scheme 30) [46]. Such azo dyes were assigned the azo tautomeric structure as their 1H NMR spectra showed signal at d 5.5 assignable to NH2 protons and a broad signal at d 12.0 assignable to pyrazole NH proton.

Ph

Me

RCOC(Cl)=NNH

N H Ph

1M, N

H

76

N

NNHAr EtOH / AcONa

S

N

Me

90

Scheme 29

NH2

Ph + R-CO-C=N-N

- HCl Me N

N N 86

O

ArN2Cl

Me N

Me

O

N COR

R: M, CH3 ; N, EtO

Scheme 27

N

N Het

N

N

87

R

Me N H

N

Me

N

S 91

Synthesis and tautomerism of heterocyclic azo compounds Me Ar-N=N

Me NH2 NH2

CN

263

NH2

NMe 2

Ar-N=N N

R

N 92

SCH2COPh

N

R

94

NNHAr

X

N H

CHO

X

R = Me, Ph

N

R

X = CHO 98

i

N

i= N

NH2NH2

Cl

X = EtOCO

NH2

N H

N=N-Ar

NH

N

CN

N

N

97

96

Me Ar-N=N

N

i

ArN2Cl

O N=N-Ar

X : A, CHO; B, EtOCO

99

93

Scheme 32 Scheme 30

A study of the electronic absorption spectra of 3-(2,4-dihydroxy-1-naphthylazo)-4,6-dimethylpyrazolo[3,4-b]pyridine 95a and 3-(2-hydroxy-1-naphthylazo)-4,6-dimethylpyrazolo-[3,4b]pyridine 95b in a number of organic solvents indicated that they exist in basic solvents as azo-hydrazone tautomeric equilibrium. However, in acetone, acetonitrile and carbon tetrachloride, they exist mainly in the arylazo tautomeric form 95A (Scheme 31) [48].

O

OH H N

N Me

N

N

Me

Me

N=N-Ar

N H

N 95C

103

N

OH N=N-Ar

Scheme 33

OH

OH H N

N Me

NH2

ArN2Cl

N

N Me

105 N

N NH2

N

O

104

N=N-Ar

N NH2

N

Me 105'

NNHAr

Scheme 34

Another synthetic strategy for 3-arylazopyrazolo[1,5a]pyrimidine dyes involves condensation of 5-amino-4-arylazopyrazole derivatives with various reagents. For example, reaction of 5-amino-4-arylazopyrazole derivatives 112 with enaminones 113 afforded the respective 3-arylazopyrazolo[1,5-a]pyrimidine dyes 114 (Scheme 36) [26,54,55].

N=N-Ar

Me

NNHAr

N Me

N

N

Me N=N-Ar

102

N Me

N

OH

N

Me

OH

Ar-N=N

N

OH

N 101

OH

N

N

Me

100

Pyrazolo[1,5-a]pyrimidines Coupling of enaminal 96A and enamino ester 96B each with diazonium salts gave the respective hydrazones 97A and 97B, respectively (Scheme 32). Condensation of the latter hydrazones each with aminopyrazole yielded the respective arylazo derivatives of pyrazolo[1,5-a]pyrimidines 98 and 99, respectively (Scheme 32) [49,50]. No discussion of the tautomerism of products 99, however, was presented. Three series of mono-arylazo- and bis-arylazo- derivatives of pyrazolo[1,5-a]pyrimidine ring system 101–103 were prepared via coupling of the respective diazotized anilines with 2-methyl-pyrazolo[1,5-a]pyrimidin-2,7(1H,7H)-dione 100 (Scheme 33) [51]. Such derivatives were reported to exist predominantly in the indicated arylazohydroxy tautomeric form. Similarly, a series of 2-amino-3-arylazo-7-hydroxy-5methyl-pyrazolo[1,5-a]pyrimidines 105 was prepared via coupling the respective diazotized anilines with 2-amino-7-hydroxy-5-methyl-pyrazolo[1,5-a]pyrimidine 104 (Scheme 34) [52]. Their electronic spectra in different solvents indicated that they exist mainly in the azo tautomeric form 105. Also, hydrazinolysis of 106 gave 5-amino-4-phenylpyrazole 107. Cyclization of the latter with diethylmalonate afforded 108 which, upon coupling with diazotized anilines, afforded the respective 6-arylazo derivatives 109 [53]. Treatment of the latter with Phosphorusoxy chloride gave 110 which, upon reaction with secondary amines, yielded 111 (Scheme 35) [53].

ArN2Cl

O

Ar-N=N

N H

95A

N N

Me

95B

Ar : a, 2,4-(HO)2-1-naphthyl ; b, 2-HO-1-naphthyl

Scheme 31

N

264

A.S. Shawali Ph

Ph N 2H4.H2O PhCH(CN)CHO 106

N H

Ph

N

R2N

NH2 107

O

Cl

O

O

N=N-Ar

110

111

NH

N Cl

N=N-Ar

ArN2Cl

N

i

N

N

NR 2

O 108

Ph

N

ii

NH

N

Ph

N N

N

N

109

NNHAr

R 2N = (CH2)5 N , O(CH2CH 2)2 N

i = POCl3 , ii = R 2 NH

Scheme 35

R R

N=N-Ar

R

R

N=N-Ar

N=N-Ar Ar'COCH=CHNMe2

N N H

NH2

N N

113

Ar'

R

Ar' = 2-naphthyl

a = MeCOCH 2 COMe N

NH

O

N N H

NH2

7-(methylthio)pyrazolo[1,5-a]pyrimidine 122. Treatment of the latter with aromatic amines yielded the respective aniline derivatives 123 (Scheme 39) [57]. Reaction of ethyl arylhydrazonocyanoacetate 124 with 3amino-4-arylazo-5-substituted pyrazoles 112 afforded the bisarylazo derivatives 125 (Scheme 40) [58]. Also, reaction of cyanoacetic hydrazide with arylhydrazonomalononitrile 126 yielded 3,5-diamino-4-arylazopyrazole 117. Treatment of the latter with arylhydrazonomalononitrile afforded the corresponding 2,5,7-triamino-3,6-bis-arylazopyrazolo[1,5-a]pyrimidines 127 (Scheme 41) [55,59,60]. In a similar manner, heating a mixture of each of 5-amino-3-methyl-4-arylazopyrazoles 112 with 2-arylhydrazono-3ketiminobutyronitriles 128 yielded the respective bis-arylazo

NC-CH=CH-NR 2 115 or C-COOEt 116

HC

117

N=N-Ph

N N

NH H2 N

O

NNHPh

118A N N

R2 N

=

c = (EtOCO)2 CH 2

Scheme 38

H2 N N=N-Ph

O

b = MeCOCH 2 COOEt

121

Reaction of enaminonitrile 115 with 3,5-diamino-4-phenylazopyrazole 117 was reported to follow different regiochemistry and gave 2-amino-3-phenylazo-pyrazolo[1,5-a]pyrimidin7(4H)-one 118 (Scheme 37). The latter product was also obtained by refluxing the same pyrazole derivative 117 with ethyl propiolate 116 in pyridine [54]. This product, although it can have two possible tautomeric forms, was assigned the azo tautomeric form 118A (Scheme 37). No interpretation for this or the change in regiochemistry was given. Similar condensation of 5-amino-4-arylazopyrazole derivatives 112 with ß-diketones, ß-keto esters and diester afforded the respective 3-arylazopyrazolo[1,5-a]pyrimidine dyes 119– 121 (Scheme 38) [36,56]. Reaction of [bis(methylthio)methylene]malononitrile and ethyl 2-cyano-3,3-bis(methylthio)acrylate each with 3,5diaminopyrazole 117 in refluxing ethanol in the presence of catalytic amount of piperidine gave the corresponding

H2 N

Me

N=N-Ar

N

Scheme 36

N

119

c

120

N Me

112

Me

R = Ph, 4-pyridyl, H2 N

N

NH2

N H

O

114

112

a N

N

N

N=N-Ar

N=N-Ar

b

N

N

R

N

N O 118B

Scheme 37

Synthesis and tautomerism of heterocyclic azo compounds H2N (MeS)2C=C(CN)Z

N=N-Ar

H2N

N=N-Ar

NH2

N H

NC

Me

+ N

NH2

N H

z CN

R

N=N-Ar

N

N

MeS

117

NH Me

N N

N

265

112

122

NH Ar

Me

128

N=N-Ar

N=N-Ar

N

RNH2

N N

N

N

RNH

129 z

H2 N

Me N=N-Ar

Z = CN, EtOCO

CN

N

Scheme 42

123

Scheme 39

H2 N

N=N-Ar EtOCOC-CN N-NHAr

+ N

R

N 112 H

Reaction of 2-aminopyrimidine 130 with the hydrazonoyl chloride 1B afforded 132 and not 133 (Scheme 44) [9]. The latter structure was rejected on the basis that reactions of haloesters with 2-aminopyrimidine 130 were reported to give 134 and not 135 (Scheme 44) [9].

124

[1,2,4]Triazolo[4,3-a]pyrimidines R

N=N-Ar

Recently, Shawali et al. [63] reported one-pot synthesis of a series of 3-arylazo-[1,2,4]triazolo[4,3-a]pyrimid-5(1H)-ones 141 via reactions of 2-thiouracil derivatives 136 (R0 = H) with N-aryl arylazomethanehydrazonoyl chlorides 1O in chloroform in the presence of triethylamine at reflux. Although the studied reactions can lead to the formation of products that

N NH

N H2 N

O

125

N=N-Ar

Scheme 40

NC

H2 N

CN N

N=N-Ar

N N 117 H

126 H2 N

N=N-Ar

NH2

N

- HX ArNHN

O

N

- H 2O

N N

N N N Ar

(NC)2C=N-NHAr

NH R

N

N NH2 130

1A, E, G

NC-CH2CONHNH 2

NHAr

N

RCOC(X)=NNHAr +

N

N R

R

131

N=N-Ar 131A

N N 127

H2 N

N

N

R: A, Me; E, XC6 H4 ; G, S

NH2 N=N-Ar

Scheme 43

Scheme 41 NNHAr

derivatives of pyrazolo[1,5-a]pyrimidines 129 (Scheme 42) [58]. Imidazo[1,2-a]pyrimidines Reactions of 2-aminopyrimidine 130 with 2-oxohydrazonoyl halides 1A, G were first studied by Shawali et al. [9] and were reported to yield the respective 3-arylazoimidazo[1,2-a]pyrimidines 131 (Scheme 43). The other regioisomers 131A were discarded on the basis that reactions of 2-aminopyrimidine with a-halo ketones give 2-substituted imidazo[1,2-a]pyrimidines [9]. Other substituted 2-oxohydrazonoyl halides namely 1E were reported to react similarly with 2-aminopyrimidine 130 to give the respective 131 (Scheme 43) [15,43].

N

+

N

NNHAr

Cl

COOEt

NH2 N 130

N

O

N

1B

O

132

N N

ClCH 2 COOEt

N 133

O

N

N N

N

NNHAr

O

134

Scheme 44

N

N 135

266

A.S. Shawali O NH

ArN=N-C(X):NNHAr + 1O

R

R' = H

N SR' 136

R' = H or Me

O NH R

N=N-Ar

O

N

N

S-C=NNHAr N=N-Ar

137

R

N

N-NHAr SR'

[1,2,4]Triazolo[1,5-a]pyrimidines

140

O

R

N

N N

O

NH

N

N(Ar)NHCS-N=NAr R

N H

138 (b)

(a)

Reaction of arylhydrazonomalononitrile 144 with 3-amino1,2,4-triazole 145 afforded the respective 6-arylazo derivatives of 1,2,4-triazolo[1,5-a]pyrimidine 146 (Scheme 47) [59,60]. Recently, it was reported that condensation of 3-amino1,2,4-triazole 145 with each of arylhydrazonals 97 yielded the respective 6-arylazo derivatives of [1,2,4]triazolo[1,5-a]pyrimidines 148 and 149, respectively, (Scheme 48) [49]. Similarly, reaction of 3-amino[1,2,4]triazole 145 with 2-arylhydrazono-3-oxo-butanoate 970 in absolute ethanol afforded also the respective arylazo derivative of 1,2,4-triazolo[1,5-a]pyrimidines 1460 [50] (Scheme 48A).

Ar

N N Ar SR'

O O HS

N

N

R N N Ar Ar-N=N NH HS

R

O

N

N R

N

N N

Ar-N=N

N

Ar R

139

N=N-Ar NH

N Ar

Pyrazolo[3,4-c]pyridazines Azocoupling of diazotized 3-aminopyrazolo[3,4-c]pyridazine 150 with various aromatic amines and phenols afforded the respective azo derivatives 151 (Scheme 49) [68].

N=N-Ar

O

N

N N Ar

- R'SH

141

O

O

N

SR

ArNHN O

R' N

O

HO

H2N

CHO

X = CHO

N

X

N H

97

148

145

N

N N

N

X = EtOCO

N +

ArNHN

N

N N

N

N O NNHAr

N=N-Ar

N

HN

N O N=N-Ar

149

Scheme 48

N

R' N

N 143B

Scheme 46

146

Scheme 47

143A

R = H, Me

N=N-Ar NH2

N

N

Ar-N=N

NH2

N N

N H 145

Ar

142

N

N

N

CN

144

O R'C(X)=NNHAr

N +

ArNHN

can have either structure 139 or 141 (Scheme 45), the isolated products were assigned structure 141. Such structural assignment was based on 13C NMR and IR spectral data. For example, the 13C NMR spectra of the products 141 revealed their carbonyl carbon resonance at d 161.7–162.8 and their IR spectra showed the CO bands at 1680–1700 cm1 [63]. These values, while they are similar to those reported for the ‘‘ringacylated’’ [1,2,4]triazolo[4,3-a]pyrimidin-5-one derivatives (d 161–164 and mCO 1690 cm1), are different from those reported for the isomeric ‘‘acylimino’’ [1,2,4]triazolo[4,3-a]pyrimidin-7one analogues (d 170–175 and 1660 cm1) [64–66]. 3-Chloroformazans 1O were also reported by Shawali et al. [63] to react similarly with 2-methylthiouracils 136 (R0 = Me)

NH

H2 N

CN

Scheme 45

PhNHN

and afforded the same products 141. This finding was considered by the authors [63] to indicate that route (a) in (Scheme 45) is the most possible mechanism for the reactions of 1O with both 2-thiouracil 136 and its 2-methylthio derivative. Reaction of 5-phenylhydrazono-2-thioxopyrimidin4,6(1H,3H)-dione or its methylthio analog 142 with various hydrazonoyl halides was reported to give the respective 6phenylazo derivatives of 1H-[1,2,4]triazolo[4,3-a]pyrimidin5(4H)-one that were assigned the tautomeric structure 143A (Scheme 46) [67].

N N Ar

COMe ArNHN 97'

+ COOEt

Me

H2N N

N

HN N

Ar

145

N

N N

HO

N N

146' Ar = 4-MeC6H4

Scheme 48A

Synthesis and tautomerism of heterocyclic azo compounds + N2

Ph

N

Ph

O

N=N-Ar Me

Ar-H

N N

267

N

N 150

O

H N

N

ArN 2Cl

N

156A

O Me

H N

N

O

Scheme 49

156B

Scheme 51

Reaction of guanine 152 with diazonium salts was first reported to give 153 [69]. Later it was shown that this conclusion is erroneous and the actual structure of the products is 154 (Scheme 50) [70]. In 1991 Slouka et al. [71] prepared a series of 154 and showed that they have the arylazo tautomeric structure 154B on the basis of their 13C and 15N NMR spectra. Similar reactions of aromatic diazonium salts with theophylline 155 were reported to give 8-arylazotheophylline derivatives 156 (Scheme 51) [72]. The results of electronic absorption spectra and quantum chemical calculations of such compounds revealed that they exist in the hydrazone form 156A. Electron withdrawing substituents and polar solvents favour the azo form 156B.

Ph

O

SH

N NH 1A, E Ph

NH2

N H

157

Ph N

N H

S

N

N H

R

N

Ph Ph N

N H

158

S

R

N H

N N Ph

159

153

N

ArN 2Cl NH O

152

N

HN H2 N

O N

HN H2 N

160

H N N Ph

Recently, Shawali et al. [75] reported that reaction of 4-amino3-phenyl-1H-1,2,4-triazole-5-thiol 166 with 2-aryl-2-oxoetha nehydrazonoyl bromides 1E in ethanol in the presence of sodium ethoxide afforded the respective thiohydrazonates 167.

N

N

R

N

[1,2,4]Triazolo[3,4-b][1,3,4]thiadiazines

N N

N

N-aryl 2-aryl-2-oxo-ethanehydrazonoyl bromides 1E was reported to react with 3-amino-1,2,4-triazine 164 to afford 3arylazo-imidazo[1,2-b][1,2,4]triazine 165 via dehydrative cyclization of the initially formed amidrazone (Scheme 54) [74].

O

HN

N

Imidazo[1,2-b][1,2,4]triazines

When compound 161 was coupled with diazotized 4methoxyaniline in pyridine, it afforded the hydrazone derivative 162. When the latter compound 162 was treated with aqueous 5% potassium hydroxide, it underwent intramolecular cyclization to furnish the respective 8-arylazo-2-phenyl-4thioxo-3,4-dihydropyrazolo[1,5-a][1,3,5]triazine 163 (Scheme 53) [73].

N=N-Ar

SH

Ph

Scheme 52

Pyrazolo[1,5-a][1,3,5]triazines

O

X = Cl; Br

R: A, Me; E, Ph

Reaction of 5-amino-4-mercapto-3-phenylpyrazole 157 with N-phenyl 2-oxohydrazonoyl halides 1A, E in ethanol in the presence of triethylamine yielded 2-(phenylazo)-3-substituted7-phenylpyrazolo[4,3-b]-1,4-thiazines 158 (Scheme 52) [23]. The other regioisomeric product 159, as well as the imidazopyrazole derivative 160, were not formed [23].

H2 N

X

R

+

N

7H-Pyrazolo[4,3-b][1,4]thiazines

HN

N=N-Ar N

N Me

Imidazo[3,2-d]pyrimidines

H2 N

N

Me

155

Ar = 4-Me2 NC6 H4 ; 2-amino-1-naphthyl; 2-hydroxy-3-(RNHCO)-1-naphthyl R = Ph, 2,5-(MeO)2 , 4-ClC6 H4

ArN 2Cl

NNHAr

N

O

Me

151

N

N

N

N

O

N

N

Me

NNHAr N

N

154A

Scheme 50

N

N=N-Ar NH

154B

268

A.S. Shawali O NC

O NHCSNHCOPh

N H 161

ArN2Cl

NC

N H NNHAr

NHCSNHCOPh 162 KOH

Ar-N=N

N

O

N H

ArNHN

Ph

N

NH - HOH

O

NH

N H

N

CSNHCOPh

S 163

Scheme 53

R

N N

ArCOC(Br)=NNHAr'

+ NH2

N

- HBr

1E

164 R

R

N

N N

N

Ar'NHN

N

- H 2O

NH COAr

Ar'

N

N

N

N

Ar 165

Scheme 54

N

N

H +

Ph 166

S N NH2

N Ph

COAr

N N

ArCOC(Br):NNHAr' 1E

S

H

NNHAr'

NH2 167

- HBr N

+

- HO 2

EtONa / EtOH

Ph

N N N

S NNHAr' Ar

168 Ar' =XC6H4 X:: a, 4-MeO; b, 4-Me; c, 3-Me; d, H; e, 4-Cl; f, 3-Cl; g, 4-NO2; h, 4-MeCO; i, 4-EtOCO; j, 4-NO2

hydrazono-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl)ethane 171 (Scheme 56). The direct formation of 171 indicates that the initially formed bis-thiohydrazonates 170 undergo in situ dehydrative cyclization under the employed reaction conditions to give 171 as end products (Scheme 56). The intermediacy of 170 was confirmed by their isolation and conversion into 171. For example, reaction of 1A (Ar = Ph), taken as a typical example of the series studied, with two molar equivalents of 1,2-bis(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)ethane in benzene in the presence of triethylamine at room temperature afforded 170 (Ar = Ph) in 92% yield. When the latter ester 170 was refluxed in acetic acid for 1 h, it yielded the respective 1,2-bis(7-phenylhydrazono-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl)-ethane 171 (Ar = Ph) in 90% yield (Scheme 56) [76]. Reaction of the bis-triazolethione with one mole equivalent of N-(p-chlorophenyl) 2-oxopropanehydrazonoyl chloride 1A (Ar = 4-ClC6H4) in ethanol in the presence of sodium ethoxide yielded one product which was identified as 172 (Scheme 56). This product was used as precursor for synthesis of a series of 1-(7-(4-chlorophenylhydrazono)-7H-[1,2,4]triazolo[3,4-b][1, 3,4]thiadiazin-3-yl)-2-(7-arylhydrazono-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl)ethanes 171. Thus, treatment of 172 with N-aryl 2-oxopropanehydrazonoyl chlorides 1A in ethanol in the presence of sodium ethoxide gave after workup the corresponding 171 in an overall good yield (72–92%) (Scheme 56) [76]. Arylazo derivatives of 6,6-biheterocycles

Scheme 55

Quinolines Similar reacions of the 4-amino-1,2,4-triazole-4(1H)-thione with the hydrazonoyl bromide having electron-withdrawing substituents in the N-aryl moiety directly afforded, however, the respective 7-arylhydrazono-3,6-diaryl[1,2,4]triazolo[3,4b][1,3,4]thiadiazines 168 as end products probably via in situ dehydrative cyclization of the respective thiohydrazonates 167 [75]. The isolated thiohydrazonates 167 were converted into the respective triazolothiadiazines 168 by treatment with acetic acid (Scheme 55) [75]. Also, reaction of 1,2-bis(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)ethane 169 with two molar equivalents of each of Naryl 2-oxopropanehydrazonoyl chlorides 1A in ethanol in the presence of sodium ethoxide at room temperature gave in each case a single product proved to be the respective 1,2-bis(7-aryl-

A series of 3-arylazo-1-methylquinolines 174 was prepared by reaction of the respective diazotized anilines with 1-methylquinoline derivative 173 in ethanol in the presence of sodium acetate (Scheme 57) [77,78]. The IR spectra indicate that such dyes exist predominantly in the ketohydrazone form 174B. Isoquinolines A series of 4-arylazo-1-ethylthio-3(4H)-isoquinolinones 176 was prepared by reaction of the respective diazotized anilines with 1-ethylthio-3(4H)-isoquinolinone 175 in ethanol in the presence of sodium acetate (Scheme 58) [79]. The IR spectra and the polarographic reduction data indicate that such dyes in aqueous solution and in solid state exist predominantly in the azo form 176C.

Synthesis and tautomerism of heterocyclic azo compounds CH3 COC(Cl)=NNHAr ( CH 1A

N 2

N

269 H

N S NH2

- HCl

2 CH3 COC(Cl)=NNHAr 1A - 2 HCl

)2

169 N H S

N

N

N N NH2

CH2CH2

( CH2

N S

N N

172

N

Ar

COCH3

)2

170

+

H -2HO 2

Ar

CH3 N

1A

N

S N NH2

H N

N

H N

CH3 COC(Cl)=NNHAr' - HCl , - H2O

Ar'

H N

N

N

S

CH2CH2

N N

N

CH3

N S

N N

N

H N

Ar

CH3

171

Ar = XC6H4 X : a, 4-CH3 ; b, 3-CH3 ; c, H; d, 4-Cl; e, 3-Cl; f, 4-EtOCO; g, 4-CH 3 CO; h, 3-NO2 ; i, 4-NO2

Scheme 56

O

O

O N=N-Ar

NNHAr

ArN 2Cl N 173

Me

O

N

O

N

Me

O

Me

174A

174B

Scheme 57

Coumarins Shawali et al. [28] studied the 1H NMR, IR and UV spectra of the diazonium coupling products of 4-hydroxycoumarin 177. The results of such study indicated that such dyes exist in the keto hydrazone form 178B both in solid and solution states (Scheme 59).

N=N-Ar O

ArN 2Cl

SEt

O

N

N 175

NNHAr

O

176A

SEt

N 176B

Quinoxalines Reactions of o-phenylenediamine 179 with the various hydrazonoyl chlorides 1A, E, F, P were reported to yield the respective 2-arylazo-1,2-dihydroquinoxaline derivatives 180 (Scheme 60) [14,80–82]. The salts of the latter products are deep coloured substances similar to compounds described as dyes [80], and the free bases of 180 were reported to be unstable in contact with air oxygen and to easily undergo oxidation to the red quinoxaline derivatives 181 [80]. Reduction of the formed azo derivative 181 with sodium dithionite afforded the aminoquinoxaline derivative 182 (Scheme 60) [80]. Reaction of o-phenylenediamine 179 with ethyl N-(arylhydrazono)chloroacetates 1B was reported by several authors to yield 3-arylhydrazono-1,2,3,4-tetrahydroquinoxalin-2-ones 184 [81–83] (Scheme 60). Such products were said to exist as a mixture of two tautomeric forms as their 1H NMR spectra revealed the presence of six protons that exchange with deuterium oxide [81].

SEt N=N-Ar OH N

176C

SEt

Scheme 58

In contrast to the foregoing established findings, it was reported that reactions of o-phenylenediamine 179 with ethyl N-(arylhydrazono)chloroacetate 1B afforded ethyl 1-aryl-4Hbenzo[c][1,2,4]triazine-3-carboxylate 185 via elimination of the aromatic amino group as ammonia from the initially formed amidrazone intermediate 183 (Scheme 60) [20]. This unexpected result needs further investigation. 1-Alkylbenzimidazole 186 reacted with hydrazonoyl chlorides 1B and gave the corresponding salts 187. The latter

270

A.S. Shawali OH

OH

O N=N-Ar

NNHAr

ArN 2Cl O

O

O

O

178B

178A

177

O

O

O N=N-Ar OH

O

178C

Scheme 59

EtOCOC(Cl):NNHAr

Z

RCOC(X):NNHAr 1A, E, F, P Z=H - HX - H 2O

179

N

R

N H

NNHAr

NH2

1B

NH2

Z = H, NO2 H N

Z

NNHAr

COOEt NH2 183

Z

N N Ar 185

H N

COOEt

N H

Z

N

NHAr

189

O

R

O

NNHAr

AcONH4

190 N

R

N H

NNHAr

H N

R

N H

N=N-Ar

180

N

R

N

N=N-Ar

N

R

N

NH2 182

R : A, Me; E, XC6 H4 ; F, benzofuran-2-yl; P, MeOCO(CH 2 )3 -

Scheme 60

N ROCOC(Cl)=NNHPh + N 1B 186 R' COOR + NNHPh N HON Cl R' 187 CHO N N N Ph OH

N

191A

191B

Scheme 62

181

184

N R'

RCOC(X)=NNHAr

OH

[O] Na2S2O7

H N

NH2

CHO N NNHPh N R'

O 188A

Treatment of 2-arylhydrazonobenzo-1,4-oxazines 190 with ammonium acetate was reported to give the respective 2-arylazoquinoxaline derivatives 191 (Scheme 62) [84,85]. 4H-1,4-Benzoxazines o-Aminophenol 189 was reported to react with the hydrazonoyl halides in ethanol in the presence of sodium ethoxide to yield the respective 2-arylhydrazonobenzo-1,4-oxazine 192A or their 2-arylazo-tautomers 192B (Scheme 63) [14,23,43,83, 84]. In contrast to the foregoing literature reports, it was indicated that reaction of 2-aminophenol 189 with ethyl N-(arylhydrazono) chloroacetate 1B afforded 2-substituted 1,3,4-oxadiazines 193 (Scheme 64) [20]. This reaction requires further confirmation. Reaction of 2-aminophenol 189 with the 2-oxohydrazonoyl bromide 1R was reported to afford the tricyclic compound 194

188B NH2

Scheme 61

RCOC(X)=NNHAr

OH 189

yielded the 3,4-dihydroquinoxalin-2-one derivatives 188 when treated with aqueous sodium hydroxide in ethanol (Scheme 61) [19]. HOMO calculations of the bonding energies of the two possible tautomeric forms indicated that the ketohydrazone structure 188A is more stable than the azo form 188B [83].

H N O

R

O

NNHAr 192A

R N=N-Ar 192B

Scheme 63

N

Synthesis and tautomerism of heterocyclic azo compounds

271

as the sole end product and no arylazo-1,4-oxazine was produced (Scheme 64) [20].

the presence of base catalyst and in all cases they were reported to give the respective 2-arylazo-1,4-benzothiazine 196 (Scheme 65) [14,29,43,80,83,85–89]. In contrast to the foregoing results, it was indicated that reactions of 2-aminothiophenol 195 with N-aryl 2-oxopropane hydrazonoyl chloride 1A and ethyl N-(arylhydrazono)chloro-

4H-1,4-Benzothiazines Reactions of o-aminothiophenol 195 with the hydrazonoyl halides were studied by several groups of authors in ethanol in

NH2

Het-CH(CN)COC(Br):NNHAr

EtOCOC(Cl):NNHAr

OH

1R

1B

189 H N

NHAr N

NH2 O

COCH(CN)Het OH H N

N

N

O

NNHAr COOEt

- NH3

Ar

H N

NH

O

Ar N N

NNHAr CN

O

Het

Het 194

COOEt 193

R = Me, Ph, EtOCO,

O

,

N SO2

, O

CN

O Ar = XC6 H4 ,

N

Ph

N

O Het =

N S

C6H4 Me-p

Scheme 64 NH2

RCOC(Cl):NNHAr 1A, B

NH2 S

NNHAr COR H N

- NH3 Ar N N S

RCOC(X):NNHAr

1E, F, P, Q SH -HX, 195 - H2 O Het-CH(CN)COC(Br):NNHAr N

R

S

NNHAr

NHAr N

196A H N

COCH(CN)Het SH COR

S

197 196B H N

N

N

S 198

Ar

H N

NH

S

NNHAr CN Het

Het

R: A, Me ; B, EtO; E, XC6 H4 ; F, O

; P, MeOCO(CH2 )3 -

; Q, O

O CN Ar = XC6 H4 ,

N

N Ph C6H4 Me-p

Scheme 65

O Het =

N S

R N N

Ar

272

A.S. Shawali

acetate 1B afforded the respective 2-substituted 1,3,4-thiadiazines 197 (Scheme 65) [20,21]. Such reactions need further reinvestigation to confirm such ambiguous results. In another report, it was indicated that reaction of 2-aminothiophenol 195 with the hydrazonoyl bromide 1A, B afforded no arylazobenzothiazine; instead it yielded the tricyclic compound 198 as the sole product (Scheme 65) [90]. Treatment of 2-arylazobenzo-1,4-oxazines 190 with phosphorus pentasulfide was reported to give the respective 2-arylazo-1,4-benzothiazine derivatives 196 (Scheme 66) [84,85]. 2-Methylaminothiophenol 199 reacted similarly with N-aryl 2-oxo-2-phenylethanehydrazonoyl bromides 1E and gave the

corresponding 2-arylazo-3-phenyl-4-methylbenzothiazines 200 (Scheme 67) [86]. Pyridazino[4,3-c]pyridazines Treatment of 201 with methylhydrazine was reported to give 2,6-dimethyl-3-oxo-2,3,4,6,7,8-hexahydropyridazino[4,3-c]pyridazine-4-arylhydrazone 202. The structure of the latter was based on its IR and 1HNMR spectra together with X-ray analysis (Scheme 68) [91]. Arylazo derivatives of 5,5,6-triheterocycles Indeno[2,1-b]thiophenes

NH2

RCOC(X)=NNHAr

OH 189

N

R

O

NNHAr

Recently three series of 2-(4-substituted-phenylazo)-3-cyano8-substituted-indeno[2,1-b]thiophenes 204 were prepared by coupling diazotized 2-amino-3-cyano-8-substituted-indeno[2,1-b]thiophene 203 with dialkylaminobenzene (Scheme 69) [92].

H N

Pyrrolo[2,1-b]benzothiazoles

P2S5

190

N

R

S

R

S

NNHAr

2-Cyanomethylbenzothiazole 205 was reported to react with the bis-hydrazonoyl chlorides 1S in ethanol in the presence of sodium ethoxide to give the respective bis-hydrazone derivative 206. Oxidation of the latter with lead tetraacetate (LTA) afforded 1,2-bis-(arylazo)-3-cyanopyrrolo[2,1-b]benzothiazoles 207 (Scheme 70) [93].

N=N-Ar

196B

196A

Scheme 66

Imidazo[1,2-a]benzimidazoles NHMe + SH

O Br

199

- HO 2

Me NH

Ph NNHAr 1E Me N Ph S

COPh

- HBr

S

NNHAr

Imidazo[2,1-b]benzothiazoles

N=N-Ar 200

Scheme 67

O

AcOCH2-CH

NNHPh MeNHNH2 O

When the hydrazonoyl bromide 1G was refluxed with 2-aminobenzimidazole 208 in ethanol, it furnished 3-arylazo-2-(benzothiazol-2-yl)-1H-imidazo[1,2-a]benzimidazoles 209 (Scheme 71) [15].

O

N Me

N

N

N

Me O

NNHPh 202

201

Reactions of 2-aminobenzothiazole 210 with N-aryl 2oxopropanehydrazonoyl chloride 1A and N-aryl 2-oxo-2phenylethanehydrazonoyl bromides 1E were reported to give the respective 3-arylazoimidazo[1,2-a]benzothiazoles 211 (Scheme 72) [31]. In another report, it was indicated, however, that reaction of the hydrazonoyl chloride 1A with 2-aminobenzothiazole yielded the unexpected amidrazone derivative 214 which was not cyclized. No rationalization, however, was given [22]. When N-phenyl 2-oxo-2-(pyrazol-3-yl)ethanehydrazonoyl bromide 1H was used in reaction with 2-aminobenzothiazole 210, it was claimed that it gave rise to the formation of 2phenylazoimidazo[1,2-a]benzothiazoles 213 (Scheme 72) [29].

Scheme 68

CN

CN NH2 S X

1) NaNO2 / HCl

N S

2) RR'NC6 H5 X

203

N 204

X = O, (CN)2 C R/R' = Me / Me, Et / Et, Et / HOCH2 CH2 , HOCH2 CH2 / HOCH2 CH2

Scheme 69

NRR'

Synthesis and tautomerism of heterocyclic azo compounds N S 205

+ CH2CN

273 No rationalization was given to account for this different regiochemical result. Similar reaction of 2-aminobenzothiazole 210 with ethyl N(arylhydrazono)chloroacetate 1B afforded 212 via cyclization of the initially formed respective amidrazone (Scheme 72) [31].

ArNHN=C(Cl)-C(Cl)=NNHAr

NNHAr NNHAr N Cl CH-CN S

- HCl

1S

NNHAr NNHAr

N - HCl

S

Thiazolo[3,2-a]benzimidazoles

CN

2-Mecrapto-1H-benzimidazole 215 was reported to react with ethyl (N-arylhydrazono)chloroacetate 1B and 2-phenylamino2-oxoethanehydrazonoyl chloride 1C in the presence of base catalyst and yielded the corresponding thiohydrazonate esters 216 (Scheme 73) [23]. Acid treatment of the latter products resulted in their cyclization to give 2-arylhydrazono-thiazolo[3,2a]benzimidazol-3-one 217 (Scheme 73) [23]. Similar reaction of 2-oxopropanehydrazonoyl chloride 1A [23] and 2-oxo-2-(hetaryl)ethanehydrazonoyl bromide 1T [23,29,89,94] each with 215 afforded the respective thiohydrazonate esters 216 that cyclized upon heating to give the corresponding arylazo thiazolobenzimidazoles 218 (Scheme 73).

206 LTA

N=N-Ar N=N-Ar

N S

CN 207

Scheme 70

N

+ Het-COC(Br):NNHAr

NH2 N H 208

1H-Imidazo[1,2-c]pyrazolo[4,3-e]pyrimidines

- HBr

1G N

NNHAr N COR N H

NH

R

N - H 2O

4-Aminopyrazolo[3,4-d]pyrimidine 219 was reported by Shawali et al. [95,96] to react readily with 2-oxoalkanehydrazonoyl halides 1A and 1U to give the respective 3-arylazo-1H-imidazo[10 ,20 -c]pyrazolo[4,3-e]pyrimidines 220 (Scheme 74). When ethyl N-(arylhydrazono)chloroacetates 1B was employed in lieu of 1A or 1U, the reaction gave 221 (Scheme 74).

Ar N

N

N H

209

1H-Dipyrazolo[1,5-a:4’,3’-e]pyrimidines

N

R =

When compounds 222 were treated with hydrazine hydrate, the initially formed hydrazino derivatives 223 underwent in situ cyclization to give the respective 1H-Dipyrazolo[1,5-

S

Scheme 71

N

- HX

S

N

NNHAr COR

+ RCOC(X)=NNHAr NH2

- HX

1A, B, E, H

210 N

NH

S

NH

S R = EtO

- H 2O N

Ar N

ArNHN

- EtOH

R

N

N

N

S 211

214 - H2O R= Het

N

S

Het

212A

N=N-Ar

N

N X = Cl, Br

NNHAr O

COR

N=NAr OH

S

R : 1A, Me ; B, EtO ;E, Ph; H, N

N 213

N

212B

Scheme 72

S

CN N Ph C6H4 Me-4

274

A.S. Shawali N N H

SH

RCOC(Cl):NNHAr 1 TEA - HCl

N H

215

R = Me, Het

- H 2O

R N=N-Ar

N

N

S

N

COR

N

H N

N

S

Ar

216

R = EtO, PhNH - RH O N N Ar N H S 217A

218

OH

R : A, Me; B, EtO; C, PhNH; E, Ph; NC Me ; H, T, N N S Ph N C6H4-Me-p Ph

N=N-Ar

N S

N

217B

Scheme 73

NH2 R'

N

RCOC(X)=NNHAr 1A, U

N

EtOCOC(Cl)=NNHAr 1B

N

N Ph

Ph

R N N

N Ph

O

N

219

N

N R'

a:40 ,30 -e]pyrimidine derivatives 224. Although two possible tautomeic structures can be written for such products, their 1 H NMR data were consistent with the hydrazone structure 224B (Scheme 75) [57].

N

N=N-Ar

N

N Ph

220

N

N Ph

R' = Ph, PhCH=CH R: A, Me; U, 2-theinyl

N Ph

Arylazo derivatives of 5,6,6-triheterocycles Pyrrolo[2,1-a]isoquinolines

221A OH N

N

NNHAr

N=NAr

N 221B

Recently, reactions of 2-(6,7-diethoxy-3,4-dihydroisoquinolin1-yl)acetonitrile 225 with each of the 2-oxohydrazonoyl halides 1A, E, L, U have been examined in tetrahydrofuran in the presence of triethylamine and found to result in the formation of the respective 2-(arylazo)pyrrolo[2,1-a]isoquinoline derivatives 226 (Scheme 76) [97]. Similar reaction of the same acetonitrile derivative with ethyl N-(arylhydrazono)chloroacetate 1B affor-

Scheme 74

H2 N

N=N-Ar

H2 N

H2 N

N=N-Ar

N

N N

N

N

MeS

X

N

N

N

NH2 NH

X 223

222 X = NH2 , OH

N X

HN

CN

CN

N=N-Ar

N

H2 N

NNHAr

N N

N X

N N 224B

Scheme 75

NH2

224A NH2

Synthesis and tautomerism of heterocyclic azo compounds EtOCOC(Cl):NNHAr

275

R'

RCOC(X):NNHAr N

R'

1B

NC R'

1A, E, L, U R'

225

N

R'

N

R'

COR

NC

COOEt

NC

NNHAr

NNHAr R'

R' O

N

R'

N

R' NNHAr

NC

R

NC

N=NAr 226

227

R' = MeO, EtO

R: A, Me; E, Ph; L, 2-naphthyl; U, 2-thienyl

Scheme 76

MeO MeO

MeO

ArN2 Cl

N Ph

NC 228

N

MeO NC

N=N-Ar Ph

229

Ar = Ph, 4-MeC6 H4

Scheme 77

ded 2-(arylhydrazono)pyrrolo[2,1-a]isoquinolin-1-carbonitrile 227 (Scheme 76) [97,98]. Recently it was reported that 3-(arylazo)pyrrolo[2,1-a]isoquinoline derivatives 229 can also be prepared by coupling 2phenyl-pyrrolo[2,1-a]isoquinoline-1-carbonitrile 228 with the appropriate diazonium salts (Scheme 77) [99]. Pyrido[1,2-a]benzimidazoles

NH). In solid state such compounds were reported to exist only in the azo tautomeric form 233A (Scheme 79) because their IR spectra showed bands at v 3434–3420 and 3395– 3371 cm1. A study of the effect of substituent on their electronic spectra revealed that some of these dyes exist in a single tautomeric form and some others as an equilibrium mixture of the azo and hydrazone forms, according to the nature of the substituent [100]. Reaction of arylhydrazonomalononitrile 126 with 2-aminobenzimidazole 208 yielded 1,3-diamino-2-arylazo-pyrimido[1,2-a]benzimidazoles 234 (Scheme 80) [59]. Similarly, condensation of 2-aminobenzimidazole 208 with each of ethyl 2-arylhydrazono-3-oxo-butanoate 126A [50] and 2-arylhydrazono-3-oxopentanal 126B [60] in refluxing ethanol afforded the respective 3-arylazo derivative of pyrimido[1,2-a]benzimidazole 234A and 234B. The isomeric structure of the latter, namely 234C, was discarded on the

Reaction of arylhydrazonomalononitrile 126 with 2-cyanomethylbenzimidazole 230 was reported to give the respective 1,3-diamino-2-arylazo-4-cyano-pyrido[1,2-a]benzimidazoles 231 (Scheme 78) [62].

NH2 N N

Pyrimido[1,2-a]benzimidazoles

232

A series of 4-amino-3-arylazo-1H-benzo[4,5]imidazo[1,2-a]pyrimidin-2-ones 233A was prepared by coupling of the respective diazotized anilines with 4-amino-1H-benzo[4,5]imidazo[1,2a]pyrimidin-2-one 232 (Scheme 79) [100]. Their 1H NMR in DMSO-d6 indicated that such azo derivatives exist as a mixture of the azo and hydrazone tautomeric forms as such spectra showed two signals in the regions d 10.2–10.1 (N1–H), 11.94–10.76 (NH2) and 10.2–8.81 (imine NH and hydrazone

NH

N H

O

N H

CN 126

N 233A

Scheme 79

CN

N

+ CN

NH2

H2 N

N=N-Ar 231

230

Scheme 78

N=N-Ar

N

233B

N

CN

NH2

ArN 2Cl

N

ArNHN

O

NNHAr

N N

N H

N H

O

276

A.S. Shawali CN

N

N

+

ArNHN

N

NH2

CN

N

N H

126

234

208

NH2

H2 N

N=N-Ar

Scheme 80

N

Et-COC(=NNHAr)CHO

EtOCOC(=NNHAr)COMe

NH2 N H 208

N

N

N

N N

N 234B

N Et

N

N Ar = XC6H4 X = H, 4-NO2

N

234A

N

234C

HO

N

N

N

Et

Ar

Me

Ar Ar = 4-MeC6H4

N Ar

Scheme 80A

S

N

N

S NH2

EtOCOC(=NNHAr)COMe

N

N

Me

O N

NHN=C(Cl)COOEt

N H

1V

N Ar

Scheme 80B

basis of NOE difference that revealed that the ethyl group and benzimidazole-H are spatially proximal (Scheme 80A) [60].

NNHPh . HCl EtOCO N

O

N NHNHPh

N

N

N N N H H

N

236 -EtOH

235 O

O NHNHPh

N

Pyrimido[2,1-a]benzothiazoles Condensation of 2-aminobenzothiazole with ethyl 2-arylhydrazono-3-oxobutanoate was reported to give the respective 3arylazo derivatives of pyrimido[1,2-a]benzimidazole (Scheme 80B) [61].

+ PhNHNH2

N

N H

N

N 237

N=N-Ph

N

[O]

238

N

N

H

Scheme 81

Triazino[4,3-a]benzimidazoles Reaction of phenylhydrazine with ethyl N-((benzimidazol2-yl)hydrazono)chloroacetate 1V was reported to give the hydrochloride salt of 4-phenylhydrazono-3-oxo-[1,2,4]triazino[4,3-a]benzimidazole 236 (Scheme 81) [48]. This result requires further investigation as the expected product from cyclization of the initially formed intermediate 235 is expected to have the isomeric structure 237 or its oxidation product 238 (Scheme 81). Furo[2,3-b]quinoxalines El-Ashry et al. [101] reported that reaction of 5-phenylfuran2,3,4-(5H)-trione 239 with o-phenylenediamine gave 240

(Scheme 82). Treatment of the latter with arylhydrazine gave a mixture of the azo derivative 241 and the hydrazide 242. The 1H NMR spectra of 241 in DMSO-d6 revealed that such dyes exist as a mixture of the iminohydrazone 241A and azo-enamine forms 241B in a ratio of 3:2, respectively. For example, the spectra showed in each case three different NH proton signals at d 10.47 (NNH), 10.63 (N4-H) and 11.47 (N1-H). Attempting to acetylate 241 with acetic anhydride in pyridine at room temperature or in refluxing acetic anhydride gave 243 [101]. The 1H NMR spectra of the latter revealed that each of such dyes exist as an equilibrium mixture of the tautomeric forms 243A and 243B (Scheme 82).

Synthesis and tautomerism of heterocyclic azo compounds O

O

277

O

NH2

N

+ Ph

H2 N

O

O

N

CONHNHAr

NH2

239

Ph

240

O

O

ArNHNH2

NNHAr N

CH(OH)Ph

+ CH(OH)Ph

N

N H 241A

242

O

N=N-Ar

H N

H N

Ph Ac2O

N=N-Ar CH(OH)Ph

O

N

N H

243A

241B

NNHAr N

O

Ph O

N 243B

Scheme 82

Pyrazolo[5,1-c]benzo[1,2,4]triazines Reaction of resorcinol with diazotized 3-amino-4-phenylhydrazino-1H-pyrazolin-5-one 244 was reported to give 245. The latter was assigned the indicated hydroxyazo tautomeric form 245B although no spectral data were given to confirm this assignment (Scheme 83) [102].

H2 N N

1H-Pyrazolo[3,4-d]pyrimido[1,6-b][1,2,4]triazines 1-Phenyl-3-substituted-5-amino-4-imino-1H-pyrazolo[3,4-d]pyrimidine 248 was reported to react with each of N-aryl-2oxoalkanehydrazonoyl halides 1A, E, U to give the respective 6-arylazo-pyrazolo[3,4-d]pyrimido[1,6-b][1,2,4]triazines 249.

ArNHN

N 2Cl

+

ArNHN

245A

244

O

Ar-N=N

N N N

HO

N H 245C

N H

N H

OH

Ar-N=N

N

O

N

O

N N

OH

Scheme 83

O N N

N

NH2 N H 16

N

NH

246 O N=N-Ar

H2 N N

The arylazo derivatives 246 were prepared by either heating 247 with one molar equivalent of acrylonitrile or heating 16 with two molar equivalents of acrylonitrile (Scheme 84) [36].

N=N-Ar

N

2 CH2=CHCN

Dipyrimido[1,2-b:20 ,10 -e]pyrazoles

OH

H2 N

N=N-Ar

CH2=CHCN

N

NH

247

CH2=CHCN

O

Scheme 84

When ethyl N-(arylhydrazono)chloroacetate 1B was used in this reaction, it gave 250 (Scheme 85) [96,103]. Arylazo derivatives of 6,6,6-triheterocycles [1,2,4,5]Tetrazino[3,2-b]quinazolines N-Aryl arylazomethanehydrazonoyl chlorides 1O have been reported to react with 3-amino-2-thioxo-4(1H)quinazolinone 251a or its methylthio derivative 251b in refluxing ethanol in the presence of triethylamine (Scheme 86) [104]. Such reactions afforded the respective 3-arylazo-6H-[1,2,4,5]tetrazino[3,2b]quinazolin-6-ones 252 via elimination of hydrogen sulphide and methanethiol respectively from the initially formed amidrazone intermediates (Scheme 86). Hetarylazo- of Bi- and Tri-heterocycles

N N 245B

2-[(4-Pyrazolyl)azo]indazoles OH

Reaction of diazotized 2-aminoimidazole 253 with 3-methyl-1phenyl-5(4H)-pyrazolone 254 yielded the respective azo dye

278

A.S. Shawali NH R'

N

RCOC(X)=NNHAr N

1A, E, U

EtOCOC(Cl)=NNHAr 1B O

248 R'

Ph

N

N

H

N N

N

N Ph

NNHAr

N

N=N-Ar

N

N

N

N Ph

R

NH2

N Ph

249

N

N

H 250A

OH N=NAr

N R'

N

R' = 2-thienyl, 2-thenoyl, Ph, PhCH=CH N

R / X: A, Me / Cl; E, Ph / Br; U, 2-thienyl / Br

N Ph

N

H

N 250B

Scheme 85 O NH2 N + N SR 251

- HCl

N=NAr

O N N

TEA

ArN=N-C(Cl):NNHAr 1O

O

NH-C

N

NNHAr SR

- RSH

H N

N=NAr N

N Ar

N 252

priate 5-pyrazolone derivatives 254. Such dyes were considered to have the indicated hydrazone structure 259A (Scheme 89) [105]. Coupling of diazotized 2-aminobenzothiazole derivative 258 with the enaminonitrile yielded the coupling product 260. Hydrazinolysis of the latter with hydrazine or phenylhydrazine yielded the respective azo dyes 261 (Scheme 90) [107]. 3-[(5-Thiazolyl)azo]pyrazolo[3,4-b]pyridines

R = a, H; b, Me

Scheme 86

255. Although the latter can have three tautomeric structures 255A–C, it was assigned the indicated ketohydrazone tautomeric structure 255A (Scheme 87) [105].

Reaction of 2-amino-4-substituted-thiazole 263 with 4,6-dimethylpyrazolo[3,4-b]pyridine-3-diazonium nitrate 262 afforded the respective azo dye 264. The latter products were assigned the azo tautomeric structure although four possible tautomeric structures can be written for each of such dyes (Scheme 91) [108].

2-[(4-Pyrazolyl)azo]benzothiazoles Hydrazinolysis of 2-benzothiazolylhydrazonomalononitrile 256 was reported to give the azo dye 257 (Scheme 88) [106]. Other dyes of this series 259 were prepared by coupling the respective 2-benzothiazole-diazonium salts 258 with the appro-

S

H2 N

NH2 NH2

N

N

NHN=C(CN)2

S 257

256

Scheme 88

Me N

+

N H

N

N

O

N

N 2Cl

253

N

255A

254

Me

N N H

N H

Ph

O

N Ph

N N H

N N

N

Me N H

N 255C

HO

N Ph

Me

N N

NH

255B O

N Ph

Scheme 87

N

NH

N

N H2 N

Synthesis and tautomerism of heterocyclic azo compounds

279 the corresponding diazonium salt. Treatment of the latter with each of malononitrile and ethyl cyanoacetate yielded the respective coupling products that cyclized in situ to give 4-amino-7-methyl-3-substituted-8-(2-thiazolylazo)pyrazolo[5,1-c][1, 2,4]triazines 268. FT-IR spectra of such dyes revealed that they exist predominantly in the indicated azo-enamine tautomeric form (Scheme 93) [109].

3-[(3-Isoxazolyl)azo]pyrazolo[5,1-c][1,2,4]triazines Diazotization of 5-amino-3-methyl-pyrazole derivative 265 and coupling the resulting diazonium salt with each of malononitrile and ethyl cyanoacetate yielded the respective coupling products that cyclized in situ to give 4-amino-7methyl-8-(3-isoxazolylazo)pyrazolo[5,1-c][1,2,4]-triazines 266. FT-IR spectra of such dyes revealed also that they exist predominantly in the indicated azo-enamine tautomeric form 266 (Scheme 92) [109].

3-[(3-Pyrazolyl)azo]quinolines Coupling of diazotized 3-amino-pyrazole derivatives 269 with 2,4-dihydroxyquinoline 270 yielded the corresponding azo dye 271 (Scheme 94) [3]. The IR spectrum of such a dye showed no C‚O bands and its 1H NMR spectrum revealed NH proton signals at d 13.98–13.85 and in addition two OH

3-[(2-Thiazolyl)azo]pyrazolo[5,1-c][1,2,4]triazines Diazotization of 5-amino-3-methyl-4-(thiazolylazo)-1H-pyrazole 267 with sodium nitrite in sulfuric acid in acetic acid gave

Me

X

N

X

N

N 2Cl

S

O

N

Me

N

+

N H

S

N N

R 258 X = H, 6-Me, 6-O2N, 6-MeO

X

R = Ph, N

N

N

S 259B

N

R

Me

N

N

N

O

259A

254

N

N N HO

N R

Scheme 89

NC-CH=C(NH2)Me

N

N

N 2Cl

S

NHN=C(CN)-C(Me)=NH

S 260

258

Me

N N

S

N

H2 N

261

RNHNH2

N N R

Scheme 90 An Me

N 2 NO3 N

Me

N H

N 262

+

Me

An

N N N

S

Me

263

N

N H

264

R/ R' : H/ H, H/ Me, H/ Ph, Ph/ Ph An = 1-phenyl-2,3-dimethyl-dihydro-5-pyrazolon-4-yl

Scheme 91

NRR' S

N

RR'N

N

280

A.S. Shawali Me

OH

Me

N O +

O O Me

Me i

N

N 270

N

NH2

OH

ClN 2

Me 272

N

N

N N H

N

N N

N

N N

ii

Me

OH

N

N

H2 N

265

O

N

266

R

N i = NaNO2 / H2 SO4 / AcOH

OH

273

ii = NC-CH2 R, R = CN, EtOCO

Scheme 95

Scheme 92

3-[(5-Methyl-isoxazol-3-yl)azo]coumarins signals at d 10.41 and 19.97. On the basis of these data such dyes were assigned the indicated azo-hydroxy tautomeric structure [3]. 3-[(3-Isoxazolyl)azo]quinolines

3-[(5-Methyl-isoxazol-3-yl)azo]coumarin 277 was prepared by coupling 4-hydroxy-coumarin 276 with diazotized 3-amino-5methylisoxazole 272 (Scheme 97). This dye, on the basis of its IR (tCO 1740 cm1) and 1H NMR (d 14.7) spectral data, was assigned the keto-hydrazone form 277B [111]. 3-[(5-Thiazolyl)azo]quinolines

The title azo dye 273 was prepared by coupling 2,4-dihydroxyquinoline 270 with diazotized 3-amino-5-methylisoxazole 272 (Scheme 95). This dye was proved on the basis of its IR (no tCO) and 1H NMR (d 10.84, OH) and was assigned the indicated azo-hydroxy tautomeric form 273 [3]. Also, diazotized 3-amino-5-methyl-isoxazole 272 was coupled with 8-hydroxyquinoline 274 and gave the respective azo dye 275 (Scheme 96) [110]. N

N Me

R' S

N N

Me

R'

N

i N

R

R = CN, EtOCO i = NaNO2 / H2 SO4 / AcOH

The 3-(2-thiazolylazo)coumarin dyes 279 were prepared by coupling diazotized 2-aminothiazole derivatives in nitrosyl sulfuric acid with coumarin derivative 276 (Scheme 99) [111]. Although four possible tautomeric structures can be written for such dyes, they were assigned the azo-hydroxy forms 279A and 279B according to the nature of the substituent R. For example, the 1H NMR spectra revealed that dye 279 (R = H) exists in one tautomeric form whereas dye 279 (R = Me) exists as a mixture of two tautomers [111].

N H2 N

267

3-[(5-Thiazolyl)azo]coumarins

N

N

ii

NH2

N H

S

N N

268

R' = H, Me

ii = NC-CH2 R

Scheme 93

3-[(1,2,4-Triazol-3-yl)azo]quinolines

OH H N N + N

The 3-(2-methyl-5-thiazolylazo)quinoline-2,4-dione dye 278 was prepared by coupling diazotized 2-amino-5-methylthiazole derivative with 4-hydroxy-2(1H)quinolinone 270 (Scheme 98). In solution, this dye 278 may exist in four possible tautomeric structures. However, its FT-IR spectra showed no carbonyl band and its 1H NMR spectrum in DMSO-d6 did not show NH signal. These findings were considered as evidence that it has the indicated azo-hydroxy form in solid state and in solution [3].

OH

ClN2 R

270

269

N

H N

OH N R = H, MeS N 271

Scheme 94

OH

N

R

Similar coupling of diazotized 3-amino-1,2,4-triazole derivatives 280 with quinoline derivative 270 afforded the respective coupling products 281 (Scheme 100) [111]. On the basis of their 1H NMR spectral data such dyes were assigned the two azo-hydroxy tautomeric forms 281A and 281B according to the substituent present. For example, compound 281a (R = H) exists in one tautomeric form, namely 281A, whereas, compound 281b (R = MeS) exists as a mixture of azo-hydroxy and keto hydrazone forms 281A and 281B, respectively [111]. Recently a series of 8-hydroxy-5-[(1,2,4-triazol-3-yl)azo] quinolines 282 were prepared by the coupling of diazotized

Synthesis and tautomerism of heterocyclic azo compounds

281 O

N N

Me

N

N O + ClN 2

N

Me N

OH 274

272

275

OH

Scheme 96

OH N O + O

ClN 2

O

Me 272

276 O

N

O

N

Me

Me

O

OH N

N

N

O

O

O 277A

N H

O

277B

Scheme 97

OH N

3-amino-1,3,4-triazoles 280 with 8-hydroxyquinoline 274 (Scheme 101) [110].

+ N H

O

ClN2

S

Me

3-[(1,2,4-Triazol-3-yl)azo]coumarins

N Me

270 OH

Coupling of diazotized 3-amino-1,2,4-triazole derivatives 280 with 4-hydroxy-coumarin 276 afforded the respective coupling products 283 [111] (Scheme 102). On the basis of their 1 H NMR spectral data such dyes were reported to have one of the two tautomeric forms 283A and 283B according to the substituent present. For example, compound 283a (R = H) exists in one tautomeric form, namely 283A, whereas compound 283b (R = MeS) exists as a mixture of

S N

N

OH

N 278

Scheme 98 OH N + O

O

ClN2

R

S

276 N OH

O 279A

O

S N

N

R

S N

N

O

O R = H, Me

Scheme 99

279B

R

OH

N

282

A.S. Shawali OH H N N + 270

N H

ClN 2

O

R

N

280 N

N

OH N

N

R N

R = a, H; b, MeS

281A

N H

N H

O

N H 281B

O

N H

R

O

N H

N

N

Scheme 100

azo-hydroxy and keto hydrazone forms 283A and 283B, respectively [111].

3-[(3-Isoxazolyl)azo]pyrimido[1,2-a]benzimidazoles Reaction of diazotized 2-amino-5-methyl-isoxazole 272 with 4-amino-2-oxopyrimido[1,2-a]benzimidazole 286 yielded the respective 3-[(3-isoxazolyl)azo]-pyrimido[1,2-a]benzimidazole 287, which was considered to exist as a mixture of the two tautomeric forms 287A and 287B (Scheme 105) [112].

3-[(1,3,4-Thiadiazol-2-yl)azo]quinolines Coupling of diazotized 3-amino-1,3,4-thiadiazole derivative with 2,4-dihydroxyquinoline 270 afforded the respective azo dye 284 [111]. On the basis of its IR spectrum, which showed HO and C‚O bands, such a dye was considered to exist as a mixture of the four tautomeric forms 284A–D (Scheme 103) [111]. Also, diazotized 2-amino-1,3,4-thiadiazoles couples with 8hydroxyquinoline 274 to give the respective thiadiazolylazo derivatives 285 (Scheme 104) [110].

3-[(2-Thiazolyl)azo]pyrimido[1,2-a]benzimidazoles Coupling of diazotized 2-amino-5-substituted-thiazole with 4amino-2-oxopyrimido[1,2-a]benzimidazole 286 yielded the respective 3-[(2-thiazolyl)azo]-pyrimido[1,2-a]benzimidazoles 288, which were considered to exist as a mixture of the two tautomeric forms 288A and 288B (Scheme 106) [112].

N

N N + ClN 2

N OH

R

N H

R

N N=N N H

280

274

R = H, HS-, MeS-, Et

N 282

OH

Scheme 101

OH H N N + O 276

ClN 2

O

280 N

OH N

O 283A

R

N

N

N

N

R N H

O N

O

O R = a, H; b, MeS

Scheme 102

283B

O

N H

N R N H

Synthesis and tautomerism of heterocyclic azo compounds

283 imidazoles 289, which were also considered to exist as a mixture of the two tautomeric forms 289A and 289B (Scheme 107) [112].

OH N N + N H 270

ClN 2

O

S

2-[(5-Pyrimidinyl)azo]benzothiazoles N

N OH

N O

S N

N

N

284B

N

OH

N

3-[(2-Benzothiazolyl)azo]pyrazolo[5,1-c][1,2,4]triazines

S N

N

N H

Similar reaction of the diazonium salt, which derived from 5-aminopyrazole derivative 293, with each of malononitrile and ethyl cyanoacetate yielded the respective coupling products that cyclized in situ to give 4-amino-7-methyl-8-(2-benzothiazolylazo)pyrazolo[5,1-c][1,2,4]triazines 294. FT-IR spectra of such dyes revealed that they exist predominantly in the indicated azo-enamine tautomeric form 294 (Scheme 110) [109].

OH

N

O

N H 284C

N

O

S N

N H

O

N H

284A

Diazotized 2-aminobenzothiazole was reported to couple with 4-hydroxy-6-methyl-2-thiouracil 136 to give the respective azo dyes 290, which were assigned the indicated azo-tautomeric structure (Scheme 108) [113]. Recently, it was reported that diazotized 3-aminopyridine 291 was coupled with 8-hydroxyquinoline 274 and gave the respective azo dye 292 (Scheme 109) [110].

S

N

OH

N

N

284D

Scheme 103

N N + N OH

ClN 2

3-[(2-Benzimidazolyl)azo]quinolines

R

S

274

3-[(2-Benzimidazolyl)azo]-2,4-dihydroxyquinoline 296 was prepared by coupling 2,4-dihydroxyquinoline 270 with diazotized 2-aminobenzimidazole 295 (Scheme 111). The 1H NMR of this dye in DMS-d6 revealed signals at d 13.98 (NH) and 10.41 (OH), which indicate that such a dye exists as the azoenol form [3].

N

N

N=N S

R R = H, HS-, MeS-, Et 285

N OH

3-[(2-Benzothiazolyl)azo]quinolines

Scheme 104

3-[(2-Benzothiazolyl)azo]quinolines 297 were prepared by coupling 2,4-dihydroxyquinoline 270 with diazotized 2-aminobenzothiazoles. The 1H NMR of this dye in DMS-d6 revealed a broad signal at d 10.37–10.93 (OH) and its IR spectrum showed no carbonyl absorption band. Such data indicate that such a dye exists in the indicated azo-enol form 297 (Scheme 112) [3].

3-[([1,2,4]Triazol-3-yl)azo]pyrimido[1,2-a]benzimidazoles Similar coupling of diazotized 2-amino-5-substituted-[1,2,4]triazole with 4-amino-2-oxopyrimido[1,2-a]benzimidazole 286 yielded the respective 3-[(3-triazolyl)azo]-pyrimido[1,2-a]benz-

NH2 N N

Me +

N H

O 272

286

N

NH

O N N

N H

Me

Me

NH2 N

N 2Cl

N

O

N

N N

O

N H 287B

287A

Scheme 105

O N N H O

N

284

A.S. Shawali NH2 N N

N

+ N H

R

O

N 2Cl

S

286 NH2

N R

S

N N

N

N NH N N H

N

N

N H

O

N

N H

S

R

O

288B

288A

R = a, H; b, Me

Scheme 106

NH2

R

N N

+ N H

286

H N

N R

H N

N

N

NH

N

N N O

N R = a, H; b, MeS

289A

N N N H

N N H

R

H N

NH2

N

N 2Cl

N

O

N H

N

O

28 9B

Scheme 107

3-[(2-Benzimidazolyl)azo]coumarins

OH N S

N

+ N 2Cl

N

Me

SR HO

136

N

N

N

R = a, H; b, Me

N

SR N

S

Me

3-[(2-Benzimidazolyl)azo]coumarin 298 was prepared by coupling 4-hydroxycoumarin 276 with diazotized 2-aminobenzimidazole in nitrosyl sulfuric acid. The 1H NMR of this dye in DMS-d6 revealed signals at d 12.5 (OH), 14.8 (NH) and 15.3 (NH), which indicate that such a dye exists as an equilibrium mixture of azo-enol and keto-hydrazone tautomeric forms 298A and 298B, respectively (Scheme 113) [3].

290

3-[(2-Benzothiazolyl)azo]coumarins Scheme 108

N N

N

A series of 3-[(2-benzothiazolyl)azo]coumarins 299 was prepared by coupling 4-hydroxycoumarin 276 with diazotized 2-aminobenzothiazoles. The 1H NMR of this dye in DMSd6 revealed two broad signals at d 13.6–13.7 (OH) and 14.7–14.8 (NH), which indicate that each of such dyes exists as an equilibrium mixture of azo-enol and keto-hydrazone tautomeric forms 299A and 299B in DMSO-d6 (Scheme 114) [111]. 3-[(2-Benzimidazolyl)azo]pyrimido[1,2-a]benzimidazoles

N 2Cl + N OH

N

N OH

274 291

Scheme 109

292

Diazotized 2-amino-benzimidazole coupled with 4-amino-2oxopyrimido[1,2-a]benzimidazole 288 and yielded the respective 3-[(2-benzimidazolyl)azo]-pyrimido[1,2-a]benzimidazole 300, which was reported to exist as a mixture of the two tautomeric amino-azo form 300A and the imino-hydrazone form 300B (Scheme 115) [112]. For example, its 1H NMR

Synthesis and tautomerism of heterocyclic azo compounds

285

R' Me

Me

i

N

N

N N H

S

N N

S

N N N

R'

N

N

NH2

ii

N H2 N

294

293

R

i = NaNO2 / H2 SO4 / AcOH

R' = H, MeO

ii = NC-CH2 R, R = CN, COOEt

Scheme 110 OH

revealed signals at d 12.45 (NH2), 11.93 (NHCO) and 9.78 (=NH).

N + N 270

OH

ClN 2

N H

3-[(2-Benzthiazolyl)azo] pyrimido[1,2-a]benzimidazoles

295 N OH N

N

Similarly, three series of 3-[(2-benzthiazolyl)azo] pyrimido[1, 2-a]benzimidazoles 301 were prepared by coupling diazotized 2-amino-benzothiazole with 4-amino-2-oxopyrimido[1,2-a] benzimidazole 286. Such dyes were found to exist as equilibrium mixture of the two tautomeric amino-azo form 301A and the imino-hydrazone form 301B (Scheme 116) [112]. For example, its 1H NMR revealed signals at d 12.50–12.40 (NH2), 10.3–10.32 (NHCO) and 9.60–9.63 (=NH) [112].

N H

N

OH

296

Scheme 111

OH N R

+ N

OH

ClN 2

S R

270 N OH

S N

N

R = Cl, MeO, O2 N N

297

OH

Scheme 112 OH N + O

ClN 2

O

N H

276 N

N OH N

O

N

N H

O N

O

O

298B

298A

Scheme 113

O

N H

N H

286

A.S. Shawali OH N R

+ O

ClN 2

O

S R

R

276

N

N O

OH

S

S N

N

N

299A

O

O

O

O

N H

299B

R = H, MeO, O 2 N

Scheme 114

NH2 N

N

+

N

N H

N 2Cl

N H

O

286 N

N

NH2

NH N H

N N

N N

N H

O

N

N H

N N H

N N H

O

300B

300A

Scheme 115

NH2 N N

+ N H

N R N 2Cl

S

O

286

N

N N N

N N

N H 301A

R

NH

R

NH2 S

N N H

N N

O

N H

S

O 301B

R = H, EtO, O2 N

Scheme 116

Conclusion and prospects The literature survey presented herein indicates that the synthesis and tautomerism of aryl- and hetaryl-azo derivatives of the various heterocycles have attracted the interest of many research groups all over the world. Such colouring compounds seem to be promising dyes. However, the author feels that there are still several problems that need further clarification before

application of such colouring compounds in industry. For example, it should be pointed out that the observation of more than one form in the 1H NMR spectra of some compounds could be more probably explained by E/Z isomerism e.g. on the moiety C‚N–NH–Ar. A similar case of the E/Z isomerism has been recently reported by Simunek et al. [114], where the isomerism has been proved by means of multinuclear magnetic resonance using isotopically labeled compounds. Also, in most

Synthesis and tautomerism of heterocyclic azo compounds literature reports covered herein, the quantification of the position of azo-hydrazone equilibria is determined by means of NMR based on comparison of relevant NMR parameters of the equilibrium mixture with the parameters of standards. As the azo-hydrazone equilibrium mixture of a single compound proceeds only through the very fast intramolecular rearrangement of the proton between two atoms (N or O), it seems that the application of N-15 NMR spectroscopy seems to be the best method available for this purpose [115,116]. Furthermore, the literature survey revealed that there are several aspects of such colorants that still need further study. For example, the role of solvent polarity, temperature and other factors that control the existence of such tautomeric mixtures could be elaborated. Also, the tautomerism-coloristic properties correlations of such dyes need to be explored. Finally, it is hoped that this review will encourage many researchers to shed light on such problems, which will facilitate the utility of such azo colouring compounds in industry.

References [1] Shawali AS, Mosselhi MAN. Hydrazonoyl halides: useful building blocks for the synthesis of arylazoheterocycles. J Heterocycl Chem 2003;40(5):725–46. [2] Shawali AS, Abdelkader MH, Eltalbawy FMA. Synthesis and tautomeric structure of novel 3, 7-bis(arylazo)-2, 6-diphenyl1H-imidazo-[1,2-b]pyrazoles in ground and excited states. Tetrahedron 2002;58(14):2875–80. [3] Se˛ner I, Karci F, Ertan N, Kilic E. Synthesis and investigations of the absorption spectra of hetarylazo disperse dyes derived from 2,4-quinolinediol. Dyes Pigments 2006;70(2):143–8. [4] Usˇ c´umlic´ GS, Mijin DZ, Valentic´ NV, Vajs VV, Susˇ ic´ BM. Substituent and solvent effects on the UV/Vis absorption spectra of 5-(4-substituted arylazo)-6-hydroxy-4-methyl-3cyano-2-pyridones. Chem Phys Lett 2004;397(1–3):148–53. [5] Raposo MMM, Sousa AMRC, Fonseca AMC, Kirsch G. Thienylpyrrole azo dyes: synthesis, solvatochromic and electrochemical properties. Tetrahedron 2005;61(34):8249–56. [6] Takagi K, Mizuno A, Iwamoto H, Kawashima S, Nishida S, Hashikawa T, et al.. Syntheses and absorption spectra of new azo dyes containing an azulene ring. Dyes Pigments 1994;26(1): 51–60. [7] ElKholy YM, Abd El-Hafiz SA. Polyfunctionally pyrazole azo dyes: synthesis and application. Pigment Resin Technol 1994;23(4):3–5. [8] Shawali AS, Sami M, Sherif SM, Parkanyi C. Synthesis of some derivatives of imidazo[1,2-a]pyridine, pyrazolo[1,5b]imidazole and 4-(3H)quinazolinone from a-ketohydrazidoyl bromides. J Heterocycl Chem 1980;17(5):877–80. [9] Abdelhamid AO, Hassaneen HM, Shawali AS, Pa´rka´nyi C. Reactions of alpha-ketohydrazidoyl halides with some heterocyclic amines. Facile synthesis of arylazo derivatives of fused heterocycles with a bridgehead nitrogen atom. J Heterocycl Chem 1983;20(30):639–43. [10] Parkanyi C, Shawali AS. An HMO study of the azo-hydrazone tautomerism in diazonium coupling products of 5isoxazolones. J Heterocycl Chem 1980;17(5):897–903. [11] Elfahham HA, Sadek KU, Elgemeie GEH, Elnagdi MH. Novel synthesis of pyrazolo[5,1-c]-1,2,4-triazoles, imidazo[1,2-b]pyrazoles and [1,2,4]-triazolo[4,3-a]benzimidazoles. Reaction of nitrile imines with amino- and oxo-substituted diazoles. J Chem Soc Perkin Trans I 1982:2663–6. [12] Elfahham HA, Sadek KU, Elgemeie GEH, Elnagdi MH. The reactions of nitrile imines with amino- and oxo-substituted azoles. Chem Lett 1982;11(1):119–22.

287 [13] Joshi KC, Pathak VN, Sharma S. Facile synthesis of fluorine containing imidazo[1,2-a]pyridines, pyrazolo[5,1-a]imidazoles and 2-iminoarylazothiazoles through a-oxo-N-arylethanehydrazonoyl bromides. Indian J Chem 1985;24B:124–8. [14] Abdelhamid AO, Ghabrial SS, Zaki MY, Ramadan NA. Facile synthesis of fused heterocycles through 2-bromobenzofurylglyoxal-2-arylhydrazones. Arch Pharmazie 1992;325(4):205–9. [15] Farag AM, Dawood KM. One-pot synthesis of imidazo [1,2b]pyrazole, imidazo[1,2-b]-1,2,4-triazole, imidazo[1,2-a]-pyridine, imidazo[1,2-a]pyrimidine, imidazo-[1,2-a]benzimidazole and 1,2,4-triazolo-[4,3-a]benzimidazole derivatives. Heteroatom Chem 1997;8(2):129–33. [16] Hermann G, Gerhard K. 3-Aroyl-1-aryl-1H-[1,2,4]triazolo[3,4c]-1,2,4-triazole, untersuchung des bildungswegs durch ro¨ntgenstrukturanalyse und molecular modelling. Chem Ber 1987;120(6):965–77. [17] Tschitschibabin AE. Zur tautomerie des a-aminopyridins III. Bicyclische derivate der tautomeren form des a-aminopyridino mit imidazol-kern. Chem Ber. 1924 Zur tautomerie des aaminopyridins III. Bicyclische derivate der tautomeren form des a-aminopyridino mit imidazol-kern. Chem Ber. 1924;57(11):2092–101. [18] Tschitschibabin AE. Zur tautomerie des a-amino-pyridins, IV. Mitteilung: Eine Darstellungsmethode des pyrimidazols und seiner homologen. Chem Ber. 1925;58(8):1704–6. [19] Croce PD. Reactions of hydrazonoyl halides with imidazoles and benzimidazoles. J Chem Soc Perkin Trans I 1979:330–2. [20] Ibrahim MKA, Elgharib MS, Farag AM, Elghandour MRH. Reaction of ethyl chloroglyoxalate arylhydrazone with heterocyclic amidine and difunction amion derivatives. J Indian Chem Soc 1988;LXV:194–6. [21] Ibrahim MKA, Elgharib MS, Farag AM, Elghandour AH. Reactions of hydrazidoyl halides with heterocyclic amines and mercaptans. Indian J Chem 1988;27B:836–9. [22] Elgemeie GEH, Elfahham HA, Ghozlan SAS, Elnagdi MH. Synthesis of several new Pyrazolo[5,1-c][1,2,4]triazoles, imidazo [1,2-b]pyrazoles and pyrazolo[3,4-b]pyrazines. Reaction of nitrilimines with amino- and oxo-substituted azoles. II. Bull Chem Soc Jpn 1984;57(6):1650–2. [23] Abdelhamid AO, Attaby FA. Reactions with hydrazidoyl halides. IV. Synthesis of thiazolo[3,2-a ]benzimidazoles, imidazo[2,1-6]thiazoles and pyrazolo[4,3-b]thiazines. J Heterocycl Chem 1991;28(1):41–4. [24] Elfahham HA, Abdel-Latif FF, Mohamed SK. Synthesis of heterocycles through the reactions of nitrilimines with aminoand oxo-diazoles. Indian J Chem Part B Org Chem 1990;29(4):381–6. [25] Ibrahim NS, Sadek KU, Abdel-Al FA. Studies on 3,5diaminopyrazoles: Synthesis of new polyfunctionally substituted pyrazoloazines and pyrazoloazoles. Arch Pharmazie 1987;320(3):240–6. [26] Hafiz ISA. -enaminonitriles in heterocyclic synthesis: synthesis of new 1,4-dihydropyridine, pyrazolo[1,5-a]pyrimidine, aminothiophene and pyridine derivatives. Z Naturforsch Section B J Chem Sci 2000;55(3–4):321–5. [27] Elnagdi MH, Elmoghayar MRH. Reactions of a-arylhydrazono-ß-oxo-ß-phenyl-prpionitriles. J Prakt Chem 1974;316: 975–80. [28] Shawali AS, Harb NMS, Badahdah KO. A study of tautomerism in diazonium coupling products of 4hydroxycoumarin. J Heterocycl Chem 1985;22(5):1397–403. [29] Abdelhamid AO, Abdelmegeid FF, Hassan NM, Zohdi HF. Reactions of hydrazonoyl halides XI. Synthesis and reactions of 1-bromo-2-(4-cyano-5-phenyl-1-p-tolylpyrazol-3-yl)etane-1phenylhydrazone. J Chem Res 1995;(S)492–(M)3036. [30] Fisher JG, Straley JM. Monoazo heterocyclic dyes for hydrophobic fibers; British Patent, 1,159,691. Chem Abstr 1970;72:56682c.

288 [31] Abdelhamid AO, Afifi MAM. Reactions of hydrazidoyl halides: Synthesis of imidazo [2,1-b] thiazole, thiazolo [2,3-c]as-triazole and heterocyclic enaminonitriles. Phosphorus Sulfur Related Elem 1988;36(1–2):129–33. [32] Shawali AS, Abdelkhalek AA, Sayed AR. Kinetics and mechanism of dehydrochlorination of 3-chloro-1,5-diarylformazans and their mass spectra. J Chin Chem Soc 2001;48(4): 693–9. [33] Abdel Fattah AM, Daboun HA, Hussain SH. Reaction with 4,5-diphenyl-2-mercaptoimidazole: synthesis of 2-substituted thiazolo (3,2-a) imidazoles. Egypt J Chem 1983;26(5):409–16. [34] Mahfouz AAA, Elhabashy FM. New synthesis of 2-substituted imidazol[2,1-b]thiazoles and their antimicrobial activities. Arch Pharm Res 1990;13(1):9–13. [35] Elgemeie GH, Elghandour AH, Elshimy HM. Studies on aminoazoles: synthesis of pyrazolo[1,5-a]-pyrimidines and their aza derivatives. J Prakt Chem 1989;331(3):466–74. [36] Elfahham HA, Elgemeie GEH, Ibraheim YR, Elnagdi MH. Studies on 3,5-diaminopyrazoles: new routes for the synthesis of new pyrazoloazines and pyrazoloazoles. Liebigs Ann Chem 1988;1988(8):819–22. [37] Abed NM, Hafez EA, Ibrahim NS, Mustafa ME. Studies on 3,5-diaminopyrazole derivatives. Monatsh Chem Chem Mon 1985;116(2):223–8. [38] Benincori T, Sannicolo F. New access to 2-(arylazo)-, 2(arylhydrazo)- and 2-aminoindoles, benzofurans and thianaphthenes. J Org Chem 1988;53(6):1309–12. [39] Benincori T, Fusco R, Sannicolo F. New heterocyclic syntheses from alpha-halohydrazones. Rearrangements of alphaarylamino- and alpha-arylthio acylhydrazones in acid medium. Gazz Chim Ital 1990;120(10):635–9. [40] Sannicolo` F. Studies on the Fischer indole synthesis: behaviour of cyclic hydrazones of tetrahydropyridazine and pyrazoline series in polyphosphoric acid. Tetrahedron Lett 1984;25(29): 3101–2. [41] Tanaka S, Terada A. Reactions of pyridylnitrilimines with dimethyl acetylene dicarboxylate. Heterocycles 1981;16: 717–20. [42] Hassaneen HM, Shawalia AS, Elwana NM, Abounadaa NM. Synthesis of pyrazolo[3,4-d]pyridazine, pyrazolo[3,4-d]pyrimidine and imidazo[1,2-a]pyridine derivatives using hydrazonyl bromides. Org Prep Proc Int 1992;24(2):171–5. [43] Emam HA, Abdel-Hamid AA. Reactions with hydrazonoyl halides. Egypt J Pharm Sci 1997;38(4–6):511–20. [44] Elnagdi MH, Zayed EM, Khalifa MAE, Ghozlan SA. Reactions with heterocyclic amidines. VII. Synthesis of some new pyrazolo[1,5-c]-1,2,4-triazines, pyrazolo[15-a]-1,3,5triazines and pyrazolo[1,5-a]pyrimidines. Monatsh Chem 1981;112(2):245–52. [45] Ghozlan SAS, Hafez EAA, El-Bannany AAA. Studies with heterocyclic hydrazidic halides: new pyrazolo[5,1-c]-1,2,4triazoles and pyrazolo[5,1-c][1,2,4]triazines. Arch Pharmazie 1987;320(9):850–3. [46] El-Kashef HS, Sadek KU, Elnagdl MH, Alnima HH. Reactions with heterocyclic diazonium salts. Synthesis of several new fused azolotriazine derivatives. J Chem Eng Data 1982;27(1):103–4. [47] Abdel Moneam MI, Kamal El-Dean AM. Synthesis of pyridothienopyridines and arylazothienopyridines. J Chem Res 2004(1):23–6. [48] Elgemeie GEH, El Zanate AM, Mansour AKE. Reaction of (cyano)thioacetamide with arylhydrazones of b-diketones: novel synthesis of 2(1H)-pyridinethiones, thieno[2,3-b] pyridines and pyrazolo[3,4-b]pyridines. Bull Chem Soc Jpn 1993;66(2):555–61. [49] Makhseed S, Hassaneen HME, Elnagdi MH. Studies with 2(arylhydrazono)aldehydes: synthesis and chemical reactivity of mesoxalaldehyde 2-arylhydrazones and of ethyl 2-

A.S. Shawali

[50]

[51]

[52]

[53]

[54]

[55]

[56]

[57]

[58] [59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

arylhydrazono-3-oxopropionates. Z Naturforsch Section B J Chem Sci 2007;62(4):529–36. Metwally MA, Yousif MY, Ismail AM, Etman HA. The synthesis of 2-methyl-3-(p-tolylazo)-pyrimido[1,2-a]benzimidazole-4-one, 7-hydroxy-5-methyl-6-(p-tolylazo)-[1,2,4] triazolo [1,5-a]pyrimidine, 2-methylpyrazolo-[1,5-a] pyridine-5,7-(4H, 6H)dione and arylazothiopyrimidines. Heterocycles 1985;23(9):2251–4. Hanna MA, Girges MM. Heterocyclic alternatives for benzidine-based mono- and disarylazo pigments: synthesis and characterization of a novel class of pyrazolo (1,5a)pyrimidine azo pigments. J Chem Technol Biotechnol 1995;62(4):392–400. Rageh NM. Electronic spectra, solvatochromic behaviour and acidity constants of some 2-amino-3-arylazo-7-hydroxy-5methyl pyrazolo[1,5-a] pyrimidines. Can J Anal Sci Spectrosc 1997;42(6):170–7. Rangnekar DW, Puro SS. Synthesis of arylasopyrazolo[1,5a]pyrimidines and their application to synthetic fibres. J Chem Technol Biotechnol 1990;49(3):275–83. Elkholy A, Al-Qalaf F, Elnagdi MH. Regio-orientation in condensation of aminopyrazoles with 1,3-difunctional reagents: synthesis of new pyrazolo[1,5-a]pyrimidines; pyrazolo[3,4-d] pyridazines and 2,4-dihydropyrano[2,3c]pyrazoles. Arkivoc 2008;2008(14):124–31. Ghozlan SAS, Hassanien AZA. -Amino-b-(pyrid-4yl)acrylonitrile in heterocyclic synthesis: synthesis of some new pyridine, pyridone, pyrazole, thiophene, fused pyrimidine and triazine derivatives. Tetrahedron 2002;58(46):9423–9. Rangnekar DW, Puro SS. Synthesis and dyeing characteristics of 3,6-bisarylazopyrazolo[1,5-a]pyrimidines. Indian J Fiber Textil Res 1990;15:23–5. Elgemeie GEH, El-Ezbawy SE, Ali HA, Mansour AK. Novel synthesis of mercaptopurine and pentaaza-as-indacene analogues: reaction of [bis(methylthio)methylene]malonitrile and ethyl-2-cyano-3,3-bis(methylthio)acrylate with 5aminopyrazoles. Bull Chem Soc Jpn 1994;67(3):738–41. Karci F. Synthesis of disazo dyes derived from heterocyclic components. Coloration Technol 2005;121(5):275–80. Kandeel ZE. Nitriles in heterocyclic synthesis: a single-step synthesis of azolo[l,5-a] pyrimidine and benzimidazolo[1,5-a] pyridine derivatives. J Chem Res 1995(7):290–1. Al-Shiekh MA, El-Din AMS, Hafez EA, Elnagdi MH. 2Arylhydrazono-3-oxopropanals in heterocyclic synthesis: synthesis of arylazopyrazole, arylazoisoxazole and dialkylpyridazine-5,6-dicarboxylate derivatives. New one-step synthesis of arylazopyrimidines. J Heterocycl Chem 2004;41(5): 647–54. Shionogi U, Kano H, Makisumi Y. 6-(phenylazo)-striazolo[2,3-a]pyrimidines, JP 6280. Chem Abstr 1964;60: 9389h. El-Sherbeny MA. Synthesis of certain pyrimido[2,1b]benzothiazole and benzothiazolo[2,3-b]quinazoline derivatives for in vitro antitumor and antiviral activities. Arzneim Forsch 2000;50(9):848–53. Shawali AS, Elghandour AH, Sayed AR. A novel one-pot synthesis of 3-arylazo-[1,2,4]triazolo-[4,3-a] pyrimidin-5(1H)ones. Syn Commun 2001;31(5):731–40. Reiter J, Pongo´ L, Dyortsa´k P. On triazoles XI. Structure elucidation of isomeric 1,2,4-triazolopyrimidinones. Tetrahedron 1987;43(11):2497–504. Bedford GR, Taylor PJ, Webb GA. 15N NMR studies of guanidines II – the fused-in guanidine unit of some oxoheterocycles: a combined 15N NMR, 13C NMR and IR study. Magn Reson Chem 1995;33(5):389–94. Greenhill JV, Ismail MJ, Bedford GR, Edwards PN, Taylor PJ. Conformational and tautomeric studies of acylguanidines. Part

Synthesis and tautomerism of heterocyclic azo compounds

[67]

[68]

[69] [70]

[71]

[72]

[73]

[74]

[75]

[76]

[77]

[78]

[79]

[80]

[81]

[82]

2. Vibrational and carbon-13 nuclear magnetic resonance spectroscopy. J Chem Soc Perkin Trans II 1985(8):1265–74. Riyadh SM. Novel regioselective synthesis and biological activity of 6-phenylazo and 3,6-bis(arylazo)-7-hydroxy-1H[1,2,4]triazolo[4,3-a]pyrimidin-5(4H)-one. J Chin Chem Soc 2005;52(3):545–51. Deeb A, Kotb M. Pyridazine derivatives and related compounds Part 10. Reactions of 3-diazopyrazolo[3,4c]pyridazine with reactive methylene compounds and other groups. Heterocycles 2004;63(5):1143–51. Burian R. Diazoaminoverbindungen der imidazole und der Purinsubstanzen. Ber Dtsch Chem Ges 1904;37:696–707. Hung MH, Stock LM. Reactions of benzenediazonium ions with guanine and its derivatives. J Org Chem 1982;47(3): 448–53. Slouka J, Bekarek V, Lycka A. Analogues of biologically active compounds. IV: Synthesis of some 8-arylazoguanines. Arch Pharmazie 1991;324(2):133–4. Mazurek AP, Skulski L, Dobrowolski JC. Tautomeric azohydrazo equilibria in 8-arylazotheophyllines: Theoretical and experimental studies. J Mol Struct 1997;410–411:421–4. Bondock S, El Gaber Tarhoni A, Fadda AA. Heterocyclic synthesis with 4-benzoyl-1-cyanoacetylthiosemicarbazide: Selective synthesis of some thiazole, triazole, thiadiazine, pyrrylthiazole and pyrazolo[1,5-a]triazine derivatives. Monatsh Chem 2008;139(2):153–9. Joshi KC, Pathak VN, Sharma S. Synthesis of 1-acetyl/ pentafluorophenyl-3-fluorinatedaryl-5-phenyl/furfuryl-4H-4,5pyrazo lines as antifertility agents. J Indian Chem Soc 1984;61(11–12):1014–5. Shawali AS, Zeid IF, Abdelkader MH, Elsherbini AA, Altalbawy FMA. Synthesis, acidity constants and tautomeric structure of 7-arylhydrazono[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines in ground and excited states. J Chin Chem Soc 2001;48(1):65–72. Shawali AS, Abdallah MA, Mosselhi MAN, Mohamed YF. Synthesis and tautomeric structure of 1,2-bis-(7arylhydrazono-7H-[1,2,4]triazolo[3,4-b][1,3, 4]thiadiazin-3-yl) ethanes. Z Naturforsch 2002;57(5):552–6. Okada Y, Hihara T, Morita Z. Analysis of the photofading of phenylazo-aniline and phenylazo-pyridone disperse dyes on poly(ethylene terephthalate) substrate using the semiempirical molecular orbital PM5 method. Dyes Pigments 2008;79(2):111–25. Okadaa Y, Hiharab T, Moritac Z. Analysis of the catalytic fading of pyridone-azo disperse dyes on polyester using the semi-empirical, molecular orbital PM5 method. Dyes Pigments 2008;78(3):179–98. Fahmy HM, Daboun HA, Abdel Azzem M, Cauquis G, Pierre G. The electrochemical behaviour of some 1-ethylmercapto-3(4H)isoquinolones derivatives. Part I. Electroreduction of 4arylazo-1-ethylmercapto-3 (4H)isoquinolones derivatives in alcoholic aqueous media. Can J Chem 1984;62(12):2904–7. Frohberg P, Wiese M, Nuhn P. Synthesis of new tetrahydropyrazine and other heterocyclic compounds by reaction of hydrazonoyl chlorides. Arch Pharmazie 1997;330(3):47–52. Colotta V, Catarzi D, Varano F, Cecchi L, Filacchioni G, Galli A, et al.. Tricyclic heteroaromatic systems. 1,2,4-triazolo[4,3a]quinoxalines and 1,2,4-triazino[4,3-a]quinoxalines: synthesis and central benzodiazepineact receptor activity. Arch Pharmazie 1997;330(12):387–91. Colotta V, Catarzi D, Varano F, Cecchi L, Filacchioni G, Martini C, et al.. 4-Amino-6-benzylamino-1,2-dihydro-2phenyl-1,2,4-triazolo[4,3-a]quinoxalin-1-one: a new A(2A) adenosine receptor antagonist with high selectivity versus A1 receptors. Arch Pharmazie 1999;332(2):39–41.

289 [83] Pa´rka´nyi C, Abdelhamid AO, Shawali AS. Convenient synthesis of arylazo derivatives of quinoxaline, 1,4-benzothiazine and 1,4-benzoxazine. J Heterocycl Chem 1984;21(2): 521–4. [84] Ghabrial SS, Zaki MY, Eldin SM. Hydrazidoyl halides in heterocyclic synthesis: synthesis of several new pyrazolylpyrazole, pyrazolo(3,4-d)pyridazine, pyrazolo(5,1-a)astriazine andother heterocyclic derivatives. Indian J Chem Part B Org Chem 1994;33B:855–8. [85] Esmaeil NA. Reactions with coumarinohydrazidoyl halides. Egypt J Pharm Sci 1991;32(3–4):961–70. [86] MacKenzie NE, Thomson RH, Greenhalgh CW. New dyes based on 3-aryl-benzo- and -naphtho-1,4-thiazines. J Chem Soc Perkin Trans I 1980:2923–32. [87] Almirante N, Forti L. 1,4-Benzothiazine derivatives from 2aminobenzenethiol and hydrazonoyl halides. J Heterocycl Chem 1983;20(6):1523–4. [88] Frohberg P. Study of tautomeric and isomeric behaviour of new 2-arylhydrazono-1,4-benzothiazines. Heterocycles 1997;45(6):1183–90. [89] Hassan NM, Abdelhamid AO. Reactions with hydrazonoyl halides. Part 16.1 A Convenient synthesis of 1,4-benzothiazine, triazolo[4,3-a]-benzimidazole, thiazolo[3,2-a]benzimidazole and 2,3-dihydro-1,3,4-thiadiazole derivatives. J Chem Res Pt S 1997(10):350–1. [90] Ismail NA, Fekry RM, Eldin SM, Abdel Azim YN. Synthesis and reactions of several new 2-thiazolin-4-onyl hydrazidoyl halides. Phosphorus Sulfur Silicon Related Elem 1993;78(1– 4):109–18. [91] Stam CH, El Ashry E, El Kilany Y, Van der Plas HC. Heterocycles from carbohydrate precursors. Part XIX. The Xray crystal structure determination of the reaction product of 4(2-acetoxyethylidene)-4-hydroxy-2,3-dioxobutyro-1,4-lactone2-(p-bromophenylhydrazone) with methylhydrazine. J Heterocycl Chem 1980;17(3):617–9. [92] Fu TL, Wang IJ. Synthesis and substituent effects of some novel dyes derived from indeno[2,1-b]thiophene compounds. Dyes Pigments 2008;76(1):158–64. [93] Dawood KM. One-pot synthesis of novel polysubstituted pyrazole and pyrrolo[2,1-b]benzothiazole derivatives. J Chem Res Pt S 1998(3):128–9. [94] Abdelhamid AO, Metwally NH, Bishai NS. Reactions with hydrazonoyl halides XXIX: synthesis of some new 1,2,4triazolo[4,3-a]benzimidazole, thiazolo[3,2-a]benzimidazole and unsymmetrical azine derivatives. J Chem Res Pt S 2000:462–3. [95] Fahmi AA, Mekki ST, Albar HA, Shawali AS, Hassaneen HM, Abdelhamid H. A facile synthesis of some pyrazolo analogues of tricyclic purine derivatives via hydrazonoyl halides. J Chem Res Sy 1994(1):6–7. [96] Aulwan NM, Abdel-Hadi HA. N-Phenyl-c-styrylmethanohydrazonoyl chloride in the synthesis of pyrazolo [4,3-e] [1,2,4] triazolo [1,5-c] pyrimidine and imidazo [1,2-e] pyrazolo [3,4-d] pyrimidine derivatives. Zag J Pharm Sci 1995;4(1B):193–9. [97] Awad EM, Elwan NM, Hassaneen HM, Linden A, Heimgartner H. Synthesis and reactivity of 2-(6,7-diethoxy3,4-dihydroisoquinolin-1-yl)acetonitrile towards hydrazonoyl halides. Helv Chim Acta 2001;84(5):1172–80. [98] Abdelhadi HA, Elwan NM, Abdallah TA, Hassaneen HM. Pyrrolo[2,1-a]isoquinolin-3-one derivatives obtained on reinvestigation of the reaction between C-ethoxycarbonyl-Narylformohydrazonoyl chlorides with 3,4-dihydro-6,7dimethoxyisoquinoline-1-acetonitrile. J Chem Res Pt S 1996;6:292–3. [99] Abdallah TA, Dawood KM. Synthesis of annulated dihydroisoquinoline heterocycles via their nitrogen ylides. Tetrahedron 2008;64(34):7890–5.

290 [100] Karci F, Demirc¸ali A, S ß ener I, Tilki T. Synthesis of 4-amino1H-benzo[4,5]imidazo[1,2-a]pyrimidin-2-one and its disperse azo dyes. Part 1: Phenylazo derivatives. Dyes Pigments 2006;71(2):90–6. [101] Amer A, El Massry AM, Awad L, Rashed N, El Ashry ESH, Ho DM. Structure of the reaction products from dehydroascorbic acid analogues, o-phenylenediamine and arylhydrazines. X-ray molecular structure of 3-[L-threo-2,3,4triacetoxy-1-(phenylhydrazono)butyl]quinoxalin-2(1H)-one hemihydrate. J Chem Soc Perkin Trans I 1990(9):2513–8. [102] Fahmy SM, Badran AH, Elnagdi MH. Synthesis of some new azopyrazole dyes. J Chem Technol Biotechnol 1980;30(1): 390–5. [103] Fahmi AA, El-Gharib MS. Synthesis and reactions of 5-amino4-iminopyrazolo [3,4-D]-pyrimidine derivatives. Zag J Pharm Sci 1995;4(1B):272–7. [104] Abdallah MA. Convenient synthesis of 6H-[1,2,4,5]tetrazino [3,2-b]quinazolin-6-ones. Monatsh Chem 2001;132(8): 959–65. [105] Ertan N. Synthesis of some hetarylazopyrazolone dyes and solvent effects on their absorption spectra. Dyes Pigments 1999;44(1):41–8. [106] Tsai PC, Wang IJ. Synthesis and solvatochromic properties of 3,6-bis-hetarylazo dyes derived from pyrazolo[1,5-a]pyrimidine. Dyes Pigments 2008;76(3):575–81. [107] Karci F, Karci F. Synthesis and absorption spectra of some novel heterocyclic disazo dyes derived from pyridone and pyrazolone derivatives. Dyes Pigments 2008;76(1):147–57.

A.S. Shawali [108] Abdel-Latif E. Versatile synthesis of N,S-heterocycles containing the antipyrine moiety. Phosphorus Sulfur Silicon Related Elem 2006;181(1):125–39. [109] Karci F, Karci F. Synthesis of some novel pyrazolo[5,1c][1,2,4]triazine derivatives and investigation of their absorption spectra. Dyes Pigments 2008;76(1):97–103. [110] Saylam A, Seferog˘lu Z, Ertan N. Synthesis and spectroscopic properties of new hetarylazo 8-hydroxyquinolines from some heterocyclic amines. Dyes Pigments 2008;76(2):470–6. [111] Karci F, Ertan N. Synthesis of some novel hetarylazo disperse dyes derived from 4-hydroxy-2H–1-benzopyran-2-one (4hydroxycoumarin) as coupling component and investigation of their absorption spectra. Dyes Pigments 2005;64(3):243–9. [112] Karci F, Demirc¸ali A. Synthesis of 4-amino-1Hbenzo[4,5]imidazo[1,2-a]pyrimidin-2-one and its disperse azo dyes. Part 2: Hetarylazo derivatives. Dyes Pigments 2006;71(2): 97–102. [113] Jain R, Pandey P. Synthesis and polarographic behaviour of (benzothiazolylazo)pyrimidines. J Electrochem Soc India 1987;36(3):179–83. [114] Simu˚nek P, Luskova´ L, Svobodova´ M, Bertolasi V, Lycka A, Macha´cek V. Synthesis and structure of some azo coupled cyclic b-enaminones. Magn Reson Chem 2007;45(4):330–9. [115] Lycˇka A. 15N, 13C and 1H NMR spectra and azo-hydrazone tautomerism of some dyes prepared by coupling of 1naphthalenediazonium salt. Dyes Pigments 1999;43(1):27–32. [116] Lycˇka A. Multinuclear NMR of azo dyes and their metal complexes. Ann Rep NMR Spectrosc 2000;42:1–57.