Synthesis and Applications of Chalcogenoamide - IngentaConnect

Current Organic Synthesis, 2007, 4, 15-29

15

Synthesis and Applications of Chalcogenoamide: Thio-, Seleno- and Telluroamides Mamoru Koketsu1,* and Hideharu Ishihara2 1Division

of Instrumental Analysis, Life Science Research Center, Gifu University, 1-1 Yanagido, Gifu, 501-1193,

Japan 2Department

of Chemistry, Faculty of Engineering, Gifu University, 1-1 Yanagido Gifu, 501-1193, Japan

Abstract: This provides a comprehensive survey of the recent progress in the various synthetic methods of the chalcogenoamides (thioamide, selenoamide and telluroamide), their application in the preparation of heterocycles and their biological significances.

Keywords: Thioamide, selenoamide, telluroamides, heterocycle, selenazole, selenazine, thiopeptide. 1. INTRODUCTION Thioamides, selenoamides, and telluroamides are useful synthetic intermediates in many synthetic transformations. They are essential building blocks for the preparation of a number of biologically relevant peptide, heterocycles etc. In the present article, we summarized the recent progress in various synthetic methods of the thioamides, selenoamides, and telluroamides and their application in the preparation of heterocycles and their biological significances. 2. THIOAMIDE Thioamides and their use in the preparation of the heterocyclic compounds are widely reported in the literature. Molecular and crystal structures of some thioamide derivatives were confirmed by X-ray diffraction data [1-3]. Also they attract considerable interests in peptide chemistry. Lawesson’s reagent or phosphorus pentasulfide (P4S 10) is actively used for the synthesis of thiocarbonyl moieties. Their preparation methods, reactions, application in the synthesis of heterocycles and biological effects are mainly described in this article. There are several review articles regarding the thioamides [4-10].

carboxamides into thioamide group in the presence of many functional groups [12-14]. Synthesis and characterization of thiopeptides has been reported using 1. Thioacylation is an alternative possible route to endothiopeptides. The following thioacylating reagents have been reported such as thioesters, dithioesters, amino thioacids, thioacyl-benzimidazolines and nitrobenzotriazoles (Scheme 1). Thionation of the amino acid amides with 1 proceeded smoothly at room temperature and provided the thioamides in high yields. They have been converted to the N-thioacyl phtalimides 2 by treatment with phthaloyl dichloride at 0°C. The N-thioacyl phtalimides have reacted with a selection of amino acid amides including dipeptide under mild conditions (Scheme 2) [15-17]. H3CO S P

S

S

P S OCH3

Lawesson’s reagent 1

2.1. Synthesis of Thioamide Lawesson’s Reagent and Phosphorus Pentasulfide (P4S10) Lawesson’s reagent [2,4-bis(4-methoxyphenyl)-1,3,2,4dithiaphosphetane-2,4-disulfide] 1 was first reported in 1956 [11]. This reagent, commercially available, presently is used for many thionations of carbonyl group-containing compounds. This reagent is very efficient and versatile, thionating reagent for aliphatic, aromatic and unsaturated carboxamides. Lawesson’s reagent 1 can convert *Address correspondence to this author at the Division of Instrumental Analysis, Life Science Research Center, Gifu University, 1-1 Yanagido, Gifu, 501-1193, Japan; Tel: +81-58-293-2619; Fax: +81-58-293-2619; E-mail: [email protected] 1570-1794/07 $50.00+.00

Treatment of 3-N-acylamino ketones with 1 yields 4H1,3-thiazine derivatives 3 and N-(3-oxoalkyl)thioamides 4, respectively. By changing the concentration of 1, selective product has been obtained. The 4H-1,3-thiazines 3 are produced predominantly when 1 equiv. of 1 is used, while with 0.5 equiv. of 1 the thioamides 4 are mainly produced (Scheme 3) [18]. Direct thionation of amino acid derivatives has been achieved using P4S10. Direct thionation of anilide has been achieved with a mixture of P4S10 and anhydrous Na2CO 3 in THF (Scheme 4) [19]. Selective thionation of amide has been achieved using P4 S 10 in THF under ultrasound irradiation. Byproduct is absent from the phosphorus pentasulfide thionation. Thionation of the amide with Lawesson’s reagent is less selective in this reaction (Scheme 5) [20].

© 2007 Bentham Science Publishers Ltd.

16 Current Organic Synthesis, 2007, Vol. 4, No. 1

Koketsu and Ishihara OCH3

OCH3

O

O

H

H

H3 C O

N CH3 HN

NH

H3C

NH

O

CH3 H

O

CH3 N

O

H3C O

N

NH

H3 C

1, dioxane, rt

NH

S CH3 H

O

CH3 N

O

CH3

N CH3 HN

O

N

CH3

O

O

O

OCH3

OCH3

OAc

OAc

O

OAc

1, benzene

AcO

NHR OAc

OAc

NHR

reflux, 24 h

OAc

OAc

OAc

O S

R2

S

AcO

S 1, toluene

N

R2

NH2

S

N NH2

reflux, 4 h R1

R1

N

N

Scheme 1. S O

S 1

PNH

NH2

THF, rt

R

Phthaloyl dichloride

PNH

NH2

N R

K2CO3 , THF, 0°C

R

S

O

S (C 2H5) 3N or free base

N R

O 2

P=N-Protected amino acid amide

PNH

+

PNH

R'NH2 0°C, 10 min

O

NHR' R

R'NH2=Amino acid amides including dipeptide

Thiopeptides

Scheme 2. R O

R1

O

S

O N

R

N H

R2

R1

S

+ R

reflux, 24 h

N H

1

R 3

Scheme 3.

R2

1, toluene

O

PNH

4

R2

Synthesis and Applications of Chalcogenoamide

Current Organic Synthesis, 2007, Vol. 4, No. 1

NO2

17

NO2 P4S 10, Na2 CO3

O H N

N H

Boc

S H N

N H

THF, 0°C, 30 min --> rt, 2.5 h

NH2

Boc

NH2

Scheme 4. MeO

MeO O Fmoc

O

N H

O

O n

O

S

P4S 10,Ultras ound Fmoc

NH2

THF, rt, 17 h

n=1 or 2

N H

n

NH2

n=1 or 2

Scheme 5.

with morpholine via Willgerodt-Kindler reaction under microwave irradiation in 30-95% yields with solvent or without solvent (Scheme 9) [24, 25].

Isothiocyanate Several reactions of isothiocyanate with nucleophiles to give the corresponding thioamides utilizing electrophilic characteristic of center carbon of isoselenocyanates group have been reported. Addition of Grignard reagent to isothiocyanates has provided secondary thioamides 5 in 4598% yields (Scheme 6) [21]. Reaction of isothiocyanates with resorcinol derivatives in the presence of boron trifluoride-acetic acid complex for overnight at 0-5°C affords the corresponding secondary thioamides 6 in 22-97% yields (Scheme 7) [22]. N-Allylthioamides 7 are prepared by the reaction of allyl isothiocyanate with 1,3-diketones in acetonitrile solution in the presence of DBU in 36-70% yields (Scheme 8) [23].

The three component condensations of aldehydes, amines and elemental sulfur using 1-methyl-2-pyrrolidone as solvent employing microwave flash heating 100-180°C for 2-20 min afford the corresponding primary, secondary and tertiary thioamides 9 in 36% to quantitative yields (Scheme 10). Reactions using secondary and tertiary amines have afforded the corresponding thioamides in high yield, more than 90 %, while reactions with anmonia give the thioamides in low yields, 36-44% [26]. Conversion of Nitrile to Primary Thioamide Nitriles could be used as starting materials for the synthesis of primary amides. Conversion of nitrile using thionating reagent gives the corresponding primary thioamides (Scheme 11). Treatments of nitriles with gaseous hydrogen sulfide in the presence of anion exchange resin

Elemental Sulfur Elemental sulfur, S8, itself is used thionation reagent for preparations of thioamides. Thiomorpholides 8 are obtained by the reaction of nitriles or ketones and elemental sulfur

S

1. Mg/ THF ArBr 2. R-N=C=S rt, 6 h 3. H2O

Ar

N H

R

5

Scheme 6. S BF3·2CH3COOH RNCS

N H

+ R1 O

OR2

0-5°C, overnight

R1O

OR2 6

Scheme 7. O

OH

S

DBU/ CH3 CN RNCS

+ X

0-2° C, 2 h --> rt, 1-3 days

N H

X

O

O 7

Scheme 8.

R

R


Koketsu and Ishihara S

O

S8/ HN

Ar

O

Ar

N

Microwave

O

DMF, 0.5 h

8

S S8/ HN R

O R

CN

N O

Microwave No solvent, 1-4.5 h

8

Scheme 9.

+ R

S

R2

O H

H

N

S8 R

R1

N

Microwave

R2

R1

100 or 180° C, 2-20 min

9

Scheme 10. S H2S/Dowex 1X8 SHR

CN

R MeOH or EtOH/H2O

NH2 10

rt, 0.5-6 h

S 70% NaHS/MgCl2 6H2O R

CN DMF or MeOH rt, 0.5-4 h

R

NH2 10

S (NH4 )2S R

CN

R

MeOH 80 or 130° C, 15-30 min

NH2 10

Scheme 11.

(Dowex 1X8, SH- from) at room temperature give the corresponding primary thioamides 10 in 25-96% yields [27]. Treatment of nitriles with 70% sodium hydrosulfide hydrate and magnesium chloride hexahydrate in DMF or methanol affords primary thioamides in high yields [28]. Primary thioamides are obtained from the corresponding nitrile by treatment with ammonium sulfide in methanol in 35% to quantitative yields [29]. Miscellaneous Thioamide Synthesis Syntheses of thioamides using other sulfur sources such as hydrogen sulfide or tetrathiomolybdate have been achieved. Imino- and iminiumtriflates 11 could be generated from secondary or tertiary amides with trifluoromethanesulfonic anhydrate in the presence of pyridine at low

temperatures. Subsequent treatment with hydrogen sulfide immediately gives rise to the corresponding secondary or tertiary thioamides 12 at low temperature. The reactions give both aliphatic as well as aromatic thioamides in 70-96% yields (Scheme 12) [30]. Dithioacids 13 are generated from carbon disulfide with Grignard reagents or alkyl lithium at 0°C. Subsequent treatment with sulfonamide in situ gives the corresponding both aliphatic as well as aromatic thioamides 14 in 77-90% yields (Scheme 13) [31]. Carboxylic acid, amine and O , O - d i e t h y l dithiophosphoric acid (3 equiv.) are refluxed in toluene. This one-pot reaction yields the corresponding secondary or tertiary thioamides 15 in 51-94% yields (Scheme 14) [32].


N

Tf 2O (1.3 equiv), Pyridine (3.5 equiv)

R1

H2S, Pyridine (3.5 equiv)

1

R

R

N

CH2Cl2, -50°C-0°C, 4 h

R 2(H)

19

S

OTf

O R


R

N

0°C, 5 min

R2(H)

R1

R 2(H) 12

11

Scheme 12. S S

C

O

S

RM

R

THF, 0°C, 30 min

SM

R1

+

N

S

-SO2

O S

Ar

R

Reflux, 18 h

R2 (H)

13 M = M gBr or Li

N 14

R1

R 2(H)

Ar = 2,4-dinitrobenzene

Scheme 13. S

O + R

(EtO) 2P(S)SH

R1 R2NH

OH

R

toluene, reflux, 6-18 hrs

N

R1

R 2(H) 15

Scheme 14.

Chlorination of amide or lactam using oxalyl chloride gives the chloro iminium salts 16 in situ. They react with tetrathiomolybdate to afford the corresponding thioamides and thiolactams 17 in short time and at low temperature in high yields. This method gives high yields of secondary or tertiary thioamides; on the other hand it gives low yield of primary thioamide [33]. Activated amides are generated by using trifluoromethanesulfonic anhydride in the presence of pyridine and are thionated with 20 wt% aqueous solution of ammonium sulfide to afford the desired secondary or tertiary thioamides 18 in high yields (Scheme 15) [34].

depending on the structure of the starting thioamide, the nature of the dielectrophile and the reaction conditions. S R

O

Cl-

Cl N

R (H)

(COCl) 2 or POCl3 R

R (H)

N

O R

N

R

R2 (H)

-40°C to rt

R

N

18

Scheme 15.

R1

R 2 (H)

2. aq(NH4) 2S, -5°C

R

N R2 17

S 1. Tf 2O, Py, CH2Cl2

MoS4 , CH2Cl2 -78°C to 25°C 15-40 min

R2 16

1

NH

S 1

CH2Cl2 , -78°C, 5 min --> 0° C, 30 min

R2

R

Reactions of primary thioamides with alkynes have been carried out. The annulation reaction of thioamides with 2alkynoates and 2,3-dienoates under the catalysis of phosphine provids thiazolines, particularly those with 2-aryl4,5-dihydro-1,3-thizoles 19 in 21-86% yields [35]. Reaction of arylthioamides with dimethyl acetylene dicarboxylate (DMAD) affords 2-aryl-4,5-dihydro-1,3-thiazol-4-ones 20 at room temperature in 36-71% yields (Scheme 16) [36].

Two nucleophilic centers in thioamides are localized on the sulfur and nitrogen atoms. An electrophilic center is associated with the thiocarbonyl carbon atom. Owing to those active centers, the different heterocyclic molecules generate by the reaction of thioamides with dielectrophiles

R

NH

1,3-Thiazole Derivatives

2.2 Heterocycles Using Thioamide

1

S

R1(H)


Koketsu and Ishihara

S

CO2Et +

Ar

Phosphine*

R

NH2

S

Ar

CO2Et

Toluene, rt, 15 h

N R

*: Bu3P or Ph3P

19 CO2CH3 S + Ar

NH2

S

Ar

CHCl3 or EtOH

OCH3 N

rt, 2 h

O

CO2CH3

O

20

Scheme 16.

Hyper iodide have been used for the syntheses of thiazoles. Cyclocondensation of thioamides and alkynyl (aryl)iodonium reagents affords 2,4-disubstituted-1,3thiazoles 21 in the presence of solid K2 CO 3 in 32-62% yields [37]. Reaction of α-λ3-iodanylketones (generated in situ from (Z)-(β-acetoxyvinyl)-(phenyl)- λ3-iodanes) with thioamides or thioureas affords 2,4-disubstituted-1,3thiazoles 22 in the presence of triethylamine in 43-95% yields (Scheme 17) [38]. Ph

S

R1

I

+ R

NH2

derivatives with thioamides or thioureas gives the corresponding 1,3-thiazoles 23 under reflux conditions in 832% yields [39]. The transformation takes place via the catalytic effect of copper (I), which generated the corresponding carbenoid from α-diazo-β-keto esters. These Cu-carbenoides react with the thiocarbonyl group of thioamides, after cyclocondensation to afford 2-aryl-1,3thiazole-5-carboxylates 24 in 62-78% yields [40]. Treatment of polymer-supported α -sulfonyloxy ketones with K2CO3

S

R N

Et2 O, 20° C, 3 h

TfO

R1

21

S

R1

Et 3N

+ R

NH2

AcO

Ph

I

MeOH, rt, 5 h

S

R N

R1

FBF3

22

R=NH2, NHPh, Ph, and Me

Scheme 17.

Treatments with some carbonyl substrates have afforded 1,3-thiazole derivatives. Reaction of dibromoacetyl

thioamides in the presence of potassium carbonate affords 1,3-thiazoles 25 in 31-93% yields (Scheme 18) [41].

O S R

N

Br 2HC

+ NH2

S

R

EtOH, reflux, 4 h

HO

HO

O R = CH3 , Ph, NH2 , NHCH3, NHPh O

S Ar

O

O CuBr

+ NH2

O

23

Ar

OR1

R

OR1

N

Toluene, reflux, 2 h

N2

S

R 24

O S + R

NH2

R1

R2 O

CH3CN, reflux, 6 h S O2

Scheme 18.

K2CO3

S

R

R1

N R2 25


S

Current Organic Synthesis, 2007, Vol. 4, No. 1 Pd2 dba3/o-biphenylP(t-Bu) 3 Cs2CO3

Br

21

S R

R

N H

N

Dioxane, 80° C, 18h

27

26 S

H3CO2C HO

N H

S

R

(CH3OCH2CH2) 2NSF 3

N

R CH2Cl2 , -20°C, 0.5-2 h

CO2CH3 29

28

R1

S H N

R

N

N H

R1

CSA (1.1 equiv.)

S R

Ph CH2 Cl2,rt, 1.5 min

O

N H

OH

S Cbz

N

31

30

H N

O

OM e

N H R

S

Method a Method b

Cbz

O

H N

S

R

32

OM e

N

Cbz

H N

O

R

33

OM e

N O

34 Ratio of 33 : 34

Method a: Ph3P, DIAD, CH2Cl2, -78->22oC, 30 min Method b: Burgess-Reagent, THF, 65oC, 10 min

Yield: 80%, 78:22 Yield: 96%, >97:3

Scheme 19.

Preparations of 1,3-thiazole derivatives by intracyclization of secondary thioamides have been achieved (Scheme 19). 2-Alkylbenzothiazole derivatives 27 have been obtained by palladium-catalyzed intramolecular cyclization of N-(o-bromophenyl)thioamides 26 in 68% to quantitative yields [42]. β-Hydroxythioamide 28 cyclodehydration reaction is carried out using [bis(2-methoxyethyl)amino] sulfur trifluoride, to afford 4,5-dihydro-1,3-thiazoles 29 in 70-97% yields [43]. The endothiopeptide amides 30 are converted into the corresponding 4H-1,3-thiazol-5-ones 31 or 4 H -1,3-thiazol-5-imines in the presence of (±)-10camphorsulfonic acid (CSA) in 88-99% yields [44-46]. Cyclodehydration of β-hydroxythioamides 32 under Mitsunobu conditions (Method a) provides peptide thiazoline in 80% yield with 78:22 ratio of 33:34 and 56% de. Treatment of β - h y d r o x y t h i o a m i d e s with M e O 2 C N S O 2 NEt 3 , the Burgess reagent, leads to the formation of thiazoline 33 in 96% yield with less than 3% epimerization at the C(2) exo methane position [47-50].

obtained by reactions of primary thioamides with α,βunsaturated ketones in 49-85% yields [51]. 2,4-Diaryl-5,6dihydro-4H-1,3-thiazines 36 are obtained by iodo-cyclization of N-homoallyl thioamides in 45-91% yields [52]. 3,4Dihydro-2H-1,3,5-thiadiazines substituted at the 3 and 6 positions 37 are synthesized by treatment of N-substituted N,N-bis(1H-1,2,3-benzotriazol-1-ylmethyl)-amines with thioamides and zinc bromide in CH2Cl2 in 43-80% yields [53].

Thiazine

β-Keto thioamides react with α,β-unsaturated aldehydes to afford debenzoylated 6-hydroxypiperidine-2-thiones 40 as major product in 45-73% yields and benzoylated 6hydroxypiperidine-2-thiones 41 as minor one in 15-27%

Syntheses of thiazine derivatives, which are sixmembered ring containing sulfur and nitrogen atoms, have been reported (Scheme 20). 1,3-Thiazine derivatives 35 are

Nitrogen-Containing Heterocycles Four- to six-membered heterocycles containing nitrogen have been obtained using thioamides. The reaction of thioamides with DMAD (5 equiv.) gives the pyrrole derivatives 3 8 in 54-70% yields [54]. Tertiary N allythioamides is converted into thioamidium salts by formation of complexes with Lewis acid. Further on treatment with LiHMDS afforded the corresponding 1,2disubstituted pyrrole 39 in 47% yield (Scheme 21) [55].



R1

S

R

O

R1

S

R2

BF3 Et 2O

R

+

NH2

R2

R4

N

CH2Cl 2, rt

R3

R3 R4

HO 35 R1

R1 Ph

I 2 (1.5 equiv.), Et3N

S Ph

N H

S N

THF, 0oC, 2 h

Ar

I

Ar 36

S

Bt N

+ R

NH2

R

ZnBr 2 (3 equiv.)

R1

S N

CH2Cl2 , rt, 48 h

Bt

N

R1

37

Bt = benzotriazoly N N N

Scheme 20. ClCH2CH2Cl or toluene R Ar

R

CO2CH3

S N H

Ar

+ reflux, 14 h

CO2CH3

MeO2C

(5 equiv.)

CO2 Me

CO2Me 38

R1

S R

N

N R1

Lewis acid

LiHMDS

CH2Cl2

THF

N

R

39

Scheme 21. R O

S

Ph

O N H

R

Et 3N, EtOH

S

+ Ph

H

S

S

CH3

LDA (2 equiv.) N(CH3) 2

THF, -78°C, 1 h

N R OH 42

Scheme 22.

H

N

OH

O

reflux, 12-14 h Ph 40

O

S

OH

+ H

R

R H

N

Ph

H

H 41

Ph


Current Organic Synthesis, 2007, Vol. 4, No. 1 Z S

N H

Y Y=O Y=CH2 Y=NH

Z

X

TTMSH (4 equiv) AIBN (1 equiv)

X

23

N

C 6H6, hv, 20 h

Y

43

Scheme 23.

yields [56]. Acyl thioamides react with LDA to give βthiolactams 42 in 67-96% yields (Scheme 22) [57]. Tandem radical cyclizations of suitably substituted Naryl thiocarbamates, thioamides and thioureas are induced by exposure to 4 equiv. of tris(trimethylsilyl)silane (TTMSH: (TMS) 3 SiH) and UV light to provide furoquinolines, isofuroquinolines, cyclopentaquinolines, indoloquinolines and related ring systems 43 in 44-88% yields (Scheme 23) [58].

2.3. Transformation of Thioamide Various conversion of thioamides by desulfurization into the corresponding amides 44 has been reported. Thioamides are converted into the corresponding amides by treatment with acids such as Caro’s acid (H2SO5) supported on silica gel (yields 61-87%) [59], oxone (yields 73-99%) [60, 61], or silver carbonate supported on celite (yields 77-98%) [62]. A variety of thioamides and thioureas are transformed to their oxo derivatives with Bi(NO3 ) 3 ·5H 2 O (yields 15-99%) (Scheme 24) [63]. Benzylic α -hydroxythioamide 4 5

S

O

R

R1

N

R2 (H)

Caro's acid (H2SO5) R

N

CH3CN, rt, 3.5-16 h

R1

R2 (H) 44

S

O

R

N

R 1(H)

R2 (H)

Oxone (1-3 equiv.) R

N

Solid phase, 5-30 h

R1(H)

R2(H) 44

Oxone = KHSO5:KHSO4 :K2 SO4 (2:1:1)

O

S R

N

R 1(H)

R2 (H)

Ag2CO3/celite (1-2 equiv.) R

N

CH3CN, rt, 5-30 h

R2 (H) 44

S R

O N

R 1(H)

R2 (H)

PFC (1.5-2.5 equiv.) R

R2(H) 44

S R

O N R2

Bi(NO3) 3 5H2O R CH3CN, reflux, 5-60 min

N R2 44

Scheme 24.

R1(H)

N

CH3 CN, reflux 1.5-7 h

PFC=Pyridinium fluorochromate

R1

R 1(H)

R1



S

O

HO

Cl

NM e2

NM e2

SOCl2 (2 equiv.) ether, rt, 19 h

45

46

Scheme 25. S R

O

R1X

N O

R

SR1

THF:H2O (10:1), reflux, 18 h 47 X=Cl, Br, I or SO4

Scheme 26.

undergoes an analogous transformation to the α-chloroamide derivative 46 with 1 equiv. of thionyl chloride, and the 46 is isolated in 98% yield (Scheme 25) [64].

ethylcarbodiimide hydrochloride (EDCI) afforded nitriles in 65-87% yields [67]. Reactions of thioamides with metal carboxylates in organic solvents enable the selective preparation of nitriles, imides or amides depending on the substitution pattern of the starting materials [68].

Thioamides are transformed into thioesters 47 through the expedient of warming them in an aqueous THF solution containing an alkylating agent. The thioesters are obtained in 20-96% yields (Scheme 26) [65].

Glycoamidines 49 are prepared by a mercury-promoted reaction of the corresponding thioamides with amines in 3387% yields [69]. N-Boc protected amidines 50 are prepared from N-Boc thioamides by treatment with base and mercury (II) chloride in 74-98% yields (Scheme 28) [70].

Thioamides have been transformed into the corresponding nitriles 48 (Scheme 27). Treatment of primary thioamides by tellurium tetrachloride or selenium tetrachloride in combination with triethylamine gives the nitriles 48 in 56-98% yields [66]. Treatment of primary amides and thioamides with 1-(3-dimethylaminopropyl)-3S R

Desulfurisation of phosphonylated thioamides is achieved by nickel chloride. The products 51 are afforded in 31-72% yields [71-73]. Treatment of methyl bromozinc-

Et3 N (5 equiv.) NH2

R

+ ECl4

C

CHCl 3, rt, 3 h

48

E=Te or Se E R

EDCI, C5H5N NH2

N

R

CH2Cl2 , rt, 14-18 h

C

N

48

E=O or S

S

O (R1COO) nM

+ R

NH2

R

C

+

N

OH

48 O

O

O

S NHR 1

R

+

(R2 COO)

nM

R

Scheme 27.

+

R2

R1

O

S R

N

CH2 Cl2, rt

+ NR1R2

(R3 COO) nM CH2 Cl2, rt

MXS

+

R1

CH2 Cl2, rt

R

O NR1R 2

+

R2

MXS

OH

O

O

+

+ R3

R3

MXS


Current Organic Synthesis, 2007, Vol. 4, No. 1 S

R

HgO

Sugar

N

R

R1R 2NH

+

Sugar CH2Cl 2, rt

H

25

NR 1R2

N 49

S

Me HgO

Sugar

N

Me

+

Sugar

RNH2 CH2Cl 2, rt

Pr

N

NR

Pr 49

NBoc

S R

N H

Boc

+

Et3N, HgCl2

R1R2 NH

R

R1

N

DMF, rt, 1-20 h

R2 50

Scheme 28. S (RO)2 P

R

R N H

NiCl2, NaBH4 CO2H

O

(RO) 2P MeOH:H2O (1:1), 15 min

N H

CO2H

O 51

S

Boc

Boc

N

N

BrZnCH2CO2Me MeO2C

THF, reflux, 1 h

52

Scheme 29.

acetate with N-(Boc)pyrrolidine-2-thione afforded good yield (33-80%) of vinylogous carbamate 52 [74] (Scheme 29).

reagents are nucleophilically introduced to the carbon atom of the thiocarbonyl group of thiamides to afford tertiary propargylamines 54 in one-pot procedure in 61-98% yields (Scheme 30) [75].

Reactions of thoiminium salts 53, generated in situ from thioamides and methyl triflate (MeOTf), with two different alkylmetals such as alkynyllithiums and alkylmagnesium bromides are investigated. The two different organometallic

S R

SMe

MeOTf N(R1) 2

Et2O, rt, 30 sec

Diastereoselective asymmetric thio-Claisen rearrangement is carried out by the reaction of thioamide with allyllic bromide. The rearrangements proceed with high syn:anti

R

N

OTf R1

53

R1

N

Et 2O or THF, rt-78°C, 2-6 h R2

R 54

Scheme 30.

C

Li

Et 2O, 0°C-rt, 30 min

R1

R 3MgX

R2C

R1 R3



R1 S

n-BuLi

R2

S

THF

Ph

R

THF, 0°C, 30 min

Li

N

R

S

electrophile Ph

R 1 R2

N

R

N

SLi

BuLi (2 equiv.) N H

R2

S

+

N

R

R1

Br

R

S

R

0°C, 30 min

E N H

Ph

E = electrophile

Scheme 31.

selectivities and good asymmetric induction [76]. Thioamide dianions (generated by the highly efficient reaction of Nbenzyl thioamides with 2 equiv. of BuLi) take place alkylation, allylation and silylation selectively at the carbon atom adjacent to the nitrogen atom of the thioamide dianions [77] (Scheme 31). 2.4. Biological Activities Several reports are available on the biological activities of thioamide derivatives. The thioamide derivatives have showed significant activities such as antituberculosis drug, anti-influenza virus activity, antitumor activity, anthelmintic activity, opioid receptor binding property, etc. [78-85].

Secondary and tertiary selenoamides 56 are obtained from amides by several methods. The secondary and tertiary selenoamides could be obtained by reaction of amides with appropriate selenating reagents such as LiAlHSeH (prepared from LiAlH4/Se), a mixture of (iBu2AlSe)2 and (iBuAlSe)n (prepared from iBu 2AlH/Se), (Me2Al)2Se (prepared from R 3 SnSeSnR 3 /Me 3 Al), selenium-Lawesson’s reagent and (Et4N)2WSe4 [91-95] (Scheme 33). Se

O R

+

Selenating reagent*

R

N

R1

R2

R2 56

3. SELENOAMIDE Reports regarding selenoamides are less than the corresponding thioamides and amides because of instability of compounds including selenium atom and their difficulty in the preparation. Recently, preparation methods to overcome their difficulties have been developed. Their reactions, preparation, application to heterocycles or biological activities have been actively investigated.

R1

N

*: LiAlHSeH, (Me 2Al) 2Se, (Et4 N) 2WSe 4 or a mixture of (iBu2AlSe) 2 and (iBuAlSe)n .

Scheme 33.

As other preparation methods of secondary and tertiary selenoamides 57, a combination of lithium alkyneselenolates and amines, one of aromatic diselenoic acid Se-methyl esters and amines, or dihalomethane with elemental selenium, NaH and amines have been established [96-104] (Scheme 34).

3.1. Synthesis of Selenoamide In order to prepare primary selenoamides 55, nitriles are excellent starting materials. The primary selenoamides are prepared by reaction of nitriles with appropriate selenating reagents such as phosphorus (V) selenide (P2Se5), hydrogen selenide (H2Se), Al2Se3, NaSeH, tris(trimethylsilyl)monoselenophosphate or potassium selenobenzoate [86-90] (Scheme 32). Se R

C N

+

Selenating reagent*

R

NH2 55

*: P2Se5 , H2 Se, Al2 Se 3, NaSeH, tris(trimethylsilyl)monoselenophosphate or potas sium selenobenzoate.

Scheme 32.

3.2. Heterocycles Using Selenoamide Selenazole and selenazine derivatives are obtained by reaction of selenoamide or selenourea with some nucleophiles [105]. Reactions of primary selenoamides with ketones, α-haloketones or haloacyl halides provided 1,3selenazole derivatives 58 [106-112] (Scheme 35). 1,3-Selenazine derivatives 59 were obtained by reactions of primary selenoamides with malonyl chloride or α,βunsaturated ketones [113-117] (Scheme 36). The selenazines prepared from aryl selenoamides are more stable than the selenazines prepared from aliphatic selenoamides because of conjugation between phenyl ring and electrons of selenazine ring.


ArC


BuLi, Se

CH

ArC

CSeLi Se

AcCl

ArC

R 1R2NH

CSeAc

R1

Ar

N R2(H) 57

Se Me 3SiC

CH

BuLi, Se

Me 3SiC

CSeLi

R1R 2NH

R1

Me 3Si

N R2(H)

57 Se

Se R' 2NH

SeCH3

NR'2 R

R

57 Se

Se, NaH, R'2NH RCHX2

R

NR' 2 57

Scheme 34. O

Se + R

R1

NH2

Se

R

HTBI*

R2

R2

N

CH2CN Reflux

R1 58

*HTBI: [Hydroxy(tosyloxy)iode]benzene, PhI(OH)OTs

O

Se R

+

NH2

R1

N

EtOH Reflux

NH2

C5H5N

X X

CH2Cl2, rt

R 2(H)

R1

58

O +

R2

X R2

Se R

Se

R

Se

R

R1

Se

R

R2

N

N O

R1 (H)

OH

58

Scheme 35. R Se

O

O

Se

OH

Et3N N

+ R

NH2

Cl

Cl

CH2Cl2 , 0°C O 59

R1

Se

R

R1 R2

Se

BF 3 Et2O +

R

O

NH2

R2

R4(H) R3

CH2 Cl2, 0°C

N HO

R3 R 4(H) 59

Scheme 36.

R1

27



4. TELLUROAMIDES

[17]

There are only limited reports of telluroamides. This is mainly due to the labilities of telluroamides under air. Crystallographic study of telluroamides and telluroiminium salts 60, introduced by a reaction of telluroamides with methyl triflate, has been investigated [93-95, 118-120] (Scheme 37).

[18] [19]

R

(Me2Al) 2Te

R1

N

R

N

Toluene

R1

R2

R2

60

N

Te R

N

THF, 0° C-rt 60

Scheme 37.

ACKNOWLEDGEMENTS This work was supported by a Grant-in-Aid for Science Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (No. 15550030 and 17550099) to which we are grateful. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9]

[10] [11] [12] [13] [14] [15] [16]

[24] [25]

LiAlH4, Te R

[23]

[26]

OTf

MeSe

[21] [22]

Te

O

[20]

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Received: March 01, 2006

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Revised: April 01, 2006

29

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Accepted: April 10, 2006