The Sulfinate-Sulfone Pummerer Rearrangement

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According to the reaction conditions the hydroxy group of hemithioacetals is replaced by chloride or acyloxy groups. Presumably sulfuranes (IV), sulfur ylides.

The Sulfinate-Sulfone Pummerer Rearrangement 1 ___________________________________________________________________________

The Sulfinate-Sulfone Pummerer Rearrangement Pummerer-Rearrangements are well-known to organic Sulfur chemists to yield internal redox products from C,H-acidic sulfoxides including desoxygenation of sulfur and oxygenation of α-carbon-hydrogen bonds. (DIA1) H3C

+

a)

S

+ (CH 3CO)2O - CH 3CO2H

O

R1 H3C

+

S

b)

+ R2COCl - R2CO2H

O

R1 H3C

+

S

c)

+ Cl-SOCl - SO2 - HCl

O

1

R

H2 C Intermediates:

O COCH3 H2C

1

SR

H2C

1

SR Cl H2C

SR _

X

1

F.G. Bordwell, B.M. Pitt, J. Am. Chem. Soc. 77, 572 (1955) 1

H2C S

for a summary, cf. S.W. Schneller, Int. J. Sulfur Chem. 8, 583 (1976)

Cl

+

S

H2C + S X1 R

X

1

R

R

SULFURANE (IV) (unsaturated)

S-YLIDE

CARBOSULFONIUM SALT

According to the reaction conditions the hydroxy group of hemithioacetals is replaced by chloride or acyloxy groups. Presumably sulfuranes (IV), sulfur ylides and carbosulfonium salts are reactive intermediates. Since thionyl chloride may be regarded as chlorosulfinic acid chloride, it was of interest whether application of sulfinyl chlorides would lead to an introduction of ambident sulfinate nucleophiles. (DIA2) H3C

+

S

O

+ R-SOCl

H3C

H3C

+

S H3 C

O SOR Cl-

SULFONIUM SALT

H3C Cl S H3C

O

SOR

SULFURANE (IV) (saturated)

H3C + Cl S H3C RSO2 oxidizing reducing species

SCH3 H2C SO2 R

- HCl

A. Senning, Chem. Commun. 1967, 64 S. Oae et al., Org. Prep. Proced. Int. 8, 119 (1976)

CH3 R

SO2 Cl + S CH3

However, as has been mentioned in literature, this was not the case with DMSO, intermolecular oxygen transfer represented the main reaction pathway. This was particularly deplorable because sulfonyl thioethers as valuable agents for nucleophilic acylations were not available by this simple way. ________________________________________________________________

The Sulfinate-Sulfone Pummerer Rearrangement 2 ___________________________________________________________________________

(DIA3) 2

R H3C

SO2

CH2

S

H3C

CH3

SO2

CH

S

CH3

H3C

SO2

1

1

R

C

S

CH3

1

R

R

CH

1

R

O

C O

2

R

2) K. Ogura, Pure & Appl. Chem. 59, 1033 (1987) 3) B. Wladislaw, L. Marzorati, Rev. Heteroatom Chem. (S. Oae) Vol. 9, MYU, Tokyo 1993

1) K. Schank, Methoden der organischen Chemie (Houben-Weyl), 4. Aufl., Bd. E11 (D. Klamann), S. 1286, Thieme, Stuttgart 1985

(DIA4) + R1SOCl tert. amine - HCl

C CH 2 R2N

S

R2N

_ O 1 C CH S R +

+ R1(2) SOCl tert. amine - HCl

1

R

C C 1(2)

R2N

SO2 R

(Z,E)

K. Schank, S. Bügler

In order to modify the basic sulfoxide we converted α-amino styrenes with sulfinylchlorides to get vinylogous sulfinamides. These conversions succeeded only in part because a secondary reaction, a desired sulfinate-sulfone Pummererreaction, ensued as fast as the first step. (DIA5) • 1 S R C CH O 1(2) R 2N + - S O S R Cl 1 R

C

C R 2N

• 1 S R + CH

_ 1 S _ R R1(2)SO2• • CH Cl-

C

R2N

R2N

CH

+

+

capto-dative stabilized

S 1) Recombination 2) - HCl

R1

C C R2N

1(2)

SO2 R

(no participation of a higher nucleophilic sulfinate R2-SO2- !)

We propose the mechanism of this rearrangement to be rather radical than ionic like that of Pummerer reactions mentioned before. Our arguments are as follows: 1) After addition of 2 equivalents of sulfinyl chloride to the vinyl amine at -78°C in presence of a tert. amine, a deep yellow color appeared which remained consistent during warming-up until -40°C. At that point, the yellow color disappeared ________________________________________________________________

The Sulfinate-Sulfone Pummerer Rearrangement 3 ___________________________________________________________________________

suddenly and at the same time colorless amine hydrochloride precipitated from the solution. 2) Addition of sulfinate of higher nucleophilicity to the yellow solution did not lead to cross reaction products. (DIA6) S

R1

C C

H3 O+

1(2)

R2N

SO2 R _ O

C CH2 S CH3 + O

SR1 C CH

CH3SOCl 1)2)

S KOH

1(2)

SO2 R

R1

H2C SO2 R1(2)

O

ß-Oxosulfoxides via acylation of methylene active sulfoxides: 1) R. Kawecki, L. Kozerski, Tetrahedron 42, 1469 (1986) 2) G.A. Russell, E.T. Sabourin, J. Org. Chem. 34, 2336 (1969)

Hydrolysis of the enamino function led to ß-oxo sulfoxides which are known from literature via other reaction pathways. Acyl cleavage of ß-oxo-sulfoxides led to the desired a-sulfonyl thioethers. (DIA7) O

O

C CH2 1

R

SR1

C

+ 2 R1SOCl - 2 HCl

+

C 1

R

SO2 A

1

1

R

R

SO2 SO2

O SO2 R1 C C SR1 (E,Z)

SO2

not isolable Trans-

+ A Sulfenylation O

O

C CH 1

R

SO 2

SR1

C

+

CH 1

R

SO2 R1

SO 2

ß-Oxosulfones instead of ß-oxosulfoxides reacted with sulfinylchlorides to show geminal di- thiofunctionalization. The resulting products, however, could not be isolated, they suffered as well isomerization to yield enolsulfonates as well transsulfenylations to yield acylated sulfonyl thioethers and acylated ß-disulfones.

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The Sulfinate-Sulfone Pummerer Rearrangement 4 ___________________________________________________________________________

(DIA8) a) SULFINATE-SULFONE PUMMERER REARRANGEMENT:

R1

O C _ • C SR1 + SO2

R1

_ O C •1 C SR + SO2

R1

O C • 1 C SR SO2

R1

O• C 1 C SR SO2 (Z,E)

• R1SO2 1

O SO2 R C 1 C SR 1

R

SO 2 (E,Z-MIXTURE)

b) ENOLATE SULFONIC ESTERIFICATION:

1

R

O C CH SR1 SO 2

1

R1SO2Cl / BASE 1

R

O SO2 R C 1 C SR SO 2 EXCLUSIVE E-ISOMER

The obtained enolsulfonates showed to be Z,E-mixtures pointing to a similar radical mechanism as discussed before. The ionic conversion of acylated α-sulfonyl thioether with sulfonyl chloride in presence of base afforded exclusively the E-isomers. (DIA9) O

O 2 R C SR1 C R3 C SO2 R1 O

R2 C 3

CH2 + 2

R1SOCl

R C O R1 CH3 4-CH 3C6H4

R2 CH3 CH3

R3 CH3 CH3

CH3 C6H5 CH3

CH3

OC2H5

CH3

OC2H5

C6H5 C6H5 C6H5

C6H5 OC2H5 OC2H5

C6H5 4-CH 3C6H4

% 76 (68)1) 78 71 (82) 2) (56) 1)

1

H2O

SR H2C

1

SO2 R

Hydrolysis instead of Trans-Sulfenylation

1) G.A. Russell, E.T. Sabourin, J. Org. Chem. 34, 2336 (1969), NaH / THF. 2) E.M. Philbin, E.R. Stuart, R.F. Timoney, T.S. Wheeler, J. Chem. Soc. 1957, 2338, yields in g.

(119)2) 66

K. Schank, S. Bügler

Since ß-oxo-sulfones are representatives of methylene active compounds consequently ß-dicarbonyl compounds were investigated under the same reaction conditions. Some of these conversions have been described in literature with open-chain ß-dicarbonyl compounds, α-sulfonyl thioether could be obtained via this sequence by a one-pot procedure in reasonable yields.

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The Sulfinate-Sulfone Pummerer Rearrangement 5 ___________________________________________________________________________

(DIA10) O C Y

CH2 + 2 R1SOCl 1) -2 HCl

Y

C O

O C SR1 C C SO2 R1 O

VARIOUS PRODUCTS via Trans-Sulfenylation

mostly not isolable CH3 Y:

a)

H 2C

C

CH2

: DIMEDONE1)

1) Isolation of 2-nitrophenyl sulfoxide: N.K. Chapowskaya, L.K. Knyazeva, N.S. Zefirov, Zh. Org. Khim. 9, 1014 (1973).

CH3 b)

CH2

: TETRONIC ACID

O

CH3 c)

O

C

K. Schank, S. Bügler, N. Schott

: MELDRUM'S ACID

O

CH3

Using cyclic ß-dicarbonyl compounds, the intermediate dithiofunctionalization products showed a very high sulfenylating property as already mentioned in connection with ß-oxosulfones. No enol sulfonates were observed in these cases. (DIA11) 1) TRANS-SULFENYLATIONS

a)

b)

Y

Y

O C SR1 C + 1 C SO2 R O O C SR1 C + C SO2 R1 O

O

O CH2

Y

O

C

C

C 1

CH SO2R

Y

+

CH SR1

Y

C

C O

C O

O

O

O

C CH SR

Y

O C SR1 C 1 C SR O

C 1

CH SO2R1

Y

C

Y

+

C O

O

2) ONE-ELECTRON OXIDATIONS (better yields with DDQ) O O O C C C SR1 1 SOCl CH SR1 2 +- 2RHCl 2Y C C Y 1 C RS C C O A O B O

R1: CH3, 4-CH3C6H 4

Y

1

1

+ R S S R On (n = 0,2)

- R1 S S R1 O

O

C

Y

O C

C C

Y C

C O

O

+2A -B

O C

C CH

Y

HC

C

Y C

O

O

However, the trans-sulfenylations were accompanied in these cases by reaction products of secondary one-electron oxidations leading to preparatively interesting dimerizations and further redox-disproportionations. Thus, for example tetraacyl ethylenes and/or ethanes were easily obtainable by this way.

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The Sulfinate-Sulfone Pummerer Rearrangement 6 ___________________________________________________________________________

(DIA12) X

O 1

O S +

SR + R1SOCl

O X = OCH 3, N

+

R1

Cl

1

R

S X O

O 1 O ; R = 4-CH3C6H4

K. Schank, S. Bügler

cf. 1) O. De Lucchi, G. Marchioro, G. Modena, J. Chem. Soc. Chem. Commun. 1984, 513. 2) R.R. King, J. Org. Chem. 45, 5347 (1980).

Further efforts in order to obtain the intermediates via a more smooth method starting from enol ethers or enamines from dimedone were fruitless. In these cases chloroorganothio dimedones as derivatives of the corresponding vicinal triketone were isolated together with the corresponding derivatives of sulfinic acid. Excellent co-working of Dr. Bügler, Dr. Schott and Thomas Heisel should be emphasized at this place, I thank you for your kind attention.

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