Epoxides, from sulfur ylids

The simplest sulfur ylids are formed from sulfonium salts 69 by deprotonation in base. These ylids react with carbonyl compounds to give epoxides.18 Nucleophilic attack on the carbonyl group 70 is followed by elimination 71 of dimethylsulfide 72 and formation of the epoxide 73. You should compare diagram 71 with diagram 23 in chapter 15. The phosphonium ylid reacted by formation of a P-0 bond and an alkene in the Wittig reaction. The sulfonium compound reacts by formation of a C-O bond 71 as the S-O bond is much weaker than the P-0 bond. The sulfonium salt 69 can be reformed by reaction of 72 with Mel. 

So what has this got to do with cyclopropanes If sulfur ylids react with enones either the epoxide 74 or the cyclopropane 76 may be formed.19 The general rule is that sulfonium ylids from 69 give epoxides but sulfoxonium ylids give cyclopropanes 76. 

Epoxides can be converted directly to episulfides by treatment with NH4SCN and ceric ammonium nitrate.Diazoalkanes, treated with sulfur, give episulfides.It is likely that R2C=S is an intermediate, which is attacked by another molecule of diazoalkane, in a process similar to that shown in 16-46. Thioketones do react with diazoalkanes to give episulfides.Thioketones have also been converted to episulfides with sulfur ylids.Carbenes, such as the dichlorocarbene from CHCI3 and base, react with thioketones to give an... 

An interesting approach to azasugars (e. g. 116 in O Scheme 31) from the epoxsides built at the anomeric centers of unprotected carbohydrates was presented recently [78]. Such epoxides (e.g. 115) were obtained with very high selectivity hy reaction of the corresponding hemi-acetals (e. g. 114) with sulfur ylid (O Scheme 31). This reaction is applicable for various sugar aldehydes [79]. 

A polymeric sulfur ylid reagent containing dimethylsulfonium methylide was synthesized by Tanimoto et al. (1967) from a copolymer of p-vinylphenylmethyl thioether, styrene, and DVB, according to Scheme 12-17. The reagent was used for the synthesis of epoxides from the carbonyl compounds. It was claimed that, in addition to simplifying the procedure for isolation of the products, the polymeric reagent is nonodorous and convenient to handle, compared to the noxious, volatile, low-molecular-weight sulfides used in classical syntheses. 

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