Unsaturated Sulphides

Unsaturated Sulphides.—Well-established preparative methods are illustrated in recent work, particularly the use of acetylenes and simple sulphur halides, or thiols, or disulphides. 

Acetylene reacts with di-isobutyl disulphide at 170—180 °C and at 12—19 atm pressure to give Bu SCH==CH2 (38%), /ra/ty-Bu SCH= CHSBu (11.6%) and its cw-isomer (3.8%), MeCH(SBu )2 (10.6%), and (Bu SCH2)2 (2.5%). ° Excess disulphide increases overall yields, and lower temperatures increase the proportions of the two major products.  

4-Nucleophilic addition of R SH to R CO C=CH in alcoholic solution containing Triton B is stereoselective, giving predominantly cw-R CO CH=CH SR even at low temperatures.  

Photochemical (589 nm) addition of thiobenzophenone at 40 °C to tetramethylallene (59) gives 2,4,4-trimethyl-3-(diphenylmethylthio)buta-diene (60) as major product, with the cyclo-adduct (61).  

The stepwise approaches used for the syntheses of acetylenic sulphides (62) illustrate some general methods. The elimination of MeSH from an 

Ogiwara, T. Mizoguchi, Y. Migita, and Y. Kanaoka, Tetrahedron Letters, 1973, 4565. 

Syntheses of vinyl sulphides based on alkynes include disulphide bond insertion (R2S2+CH=CH- RSCH=CHSR ) or thiol addition (e.g. prop-2-ynethiol+cyanoalkyne gives CH CCH2SCR==CHCN ). 

Dimethylprop-2-ynylsulphonium bromide isomerizes to the allene, which is susceptible to nucleophilic addition, giving a product mixture including the demethylation product MeSCH=CMeX (X = nucleophile). (+)-l-Adamantyl allyl ethyl sulphonium fluoroborate undergoes [2,3]-sigmatropic rearrangement to give a mixture of adamantyl ethyl and allyl sulphides and (-)-(R)-l-adamantyl pent-4-en-2-yl sulphide,i.e. with inversion at carbon chirality is transferred from S to C with at least 94% optical induction. 

Both carbonyl and alkene functions in a-benzylthio-enones (23) are reduced stereospecihcally with NaBH4 in EtOH at room temperature via 

2-addition to C=0 followed by intramolecular hydrogen transfer, possibly facilitated by activation of the intermediate alkoxyborohydride by the 

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Benzoyl hydroperoxide was used for the conversion of divinyl sulphide into divinyl sulphoxide by Levin as early as 1930. In 1954 Bateman and Hargrave reported that saturated sulphides may be oxidized to sulphoxides by means of cyclohexyl or t-butyl hydroperoxide. These authors found that in both polar and non-polar solvents oxygen transfer occurred to give quantitative yields of sulphoxides over a wide range of experimental conditions according to equation 7. It was also reported that a quantitative yield of sulphoxides was obtained from the reaction of unsaturated sulphides with t-butyl and cyclohexyl hydroperoxides in methanol. With t-butyl hydroperoxide in benzene the sulphoxide yield was in no case stoichiometric, varying from 90 to 5% under the condition chosen. 

Whereas oxygen nucleophiles gave poor yields of alkenylated products with alkenyl iodonium salts, the reactions with sulphur nucleophiles proceeded more efficiently, leading to unsaturated sulphides and sulphones. Thus, 4-t-butylcyclohexenyl phenyliodonium salts afforded with sodium thiophenoxide 4-t-butylcyclohexenyl phenyl sulphide (81%) [3] and with sodium phenylsulphinate the corresponding sulphone (29%) in the presence of 18-crown-6, the yield of the latter rose to 80% [45]. jS-Phenylsulphonylalkenyl iodonium salts with sodium phenylsulphinate at 0°C, without any catalyst, afforded Z-l,2-bis(phenylsulphonyl)alkenes, in high yield with retention of the stereochemistry [45] ... 

Such radicals may be trapped by the use of unsaturated sulphides or unsaturated solvents to give a return to the more simple kinetic behaviour. 

Thioaldehydes and Thioketones. (i) Synthesis of simple aliphatic thioalde-hydes and thioketones by reductive cleavage reactions of unsaturated sulphides. (ii) Photochemistry of thioketones. (iii) Synthesis of... 

Synthesis.—All attempts to prepare simple aliphatic thioaldehydes have until now been unsuccessful, as only the cyclic trimers or less well-defined polymeric substances have been obtained. However, Brandsma has now reported that ajS-unsaturated sulphides (1) are cleaved by alkali metals in liquid ammonia to produce the corresponding enethiols (2) in high yields. For R = H, the products (2) represent the simple aliphatic thioaldehydes (3) in what is evidently their more stable tautomeric enethiol form. Apparently the pure enethiols (2 R = H) showed no tendency to... 

The Thio-Claisen Rearrangement.—The thermal [3,3]sigmatropic rearrangement of ajS-/3 y -unsaturated sulphides, resulting in the formation of... 

Wittig reactions (Equation 3) in non-polar media can be initiated by solid-liquid phase transfer of potassium carbonate or t-butoxide with 18-crown-6. Typical salt-free product distributions (Z-disubstituted alkene predominant) are observed with non-stabilized ylidcs in THF, but they are surprisingly reversed in dichloro-methane solution. -Alkenes usually predominate in both solvents when stabilized ylides are involved. Two-phase Wittig-Horner syntheses of ajS-unsaturated sulphides etc. (Equation 5) are also crown-catalysed, as is the Darzens-type process (Equation 14). ... 

Cleavage of Unsaturated Sulphides by Carbenes and Nitrenes Photolysis.—... 

Some of these 3-aminothietan 1,1-dioxide derivatives have been claimed to be useful as anti-inflammatory ents and as sedatives. Cycloadditions of sulphenes with a/3-unsaturated sulphides also yield thietan sulphones. ° Aryl propargyl sulphones eliminate sulphur dioxide under electron impact. oftho-Substituents reduce the amount of sulphur dioxide, and a substituted thietan 1,1-dioxide intermediate was suggested. ... 

The ring opening of episulphides with allylmagnesium bromide provides a potentially valuable route to either thiolans or thians. Thus the unsaturated sulphide (14), prepared from 1-methylcyclohexene episulphide and allylmagnesium bromide, was cyclized in the presence of H2SO4 to the thiolan (15) (97%), while the thian (16) was produced in 92% yield on photolysis. 

New cyclization reactions leading to thiophens have been discovered. Especially important is Brandsma s work on the cyclization of unsaturated sulphides. 

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