Epoxides carbonyl ylids from

When the epoxide is made from a carbonyl compound, e.g. (29) (Chapter 30), the result is chain extension to the homologous aldehyde. This procedure can be carried out with sulphur ylids (30) or by the Darzens reaction with decarboxylation of the intermediate acid (31). 

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. 

Sulfoxonium ylids react with unsaturated carbonyl compounds in the same way as the stabilized ylids that you have met already do—they form cyclopropanes rather than epoxides. The example below shows one consequence of this reactivity pattern-—by changing from a sulfonium to a sulfoxonium ylid, high yields of either eposjde or cyclopropane can be formed from an unsaturated carbonyl compound (this one is the terpene carvone). 

This same disconnection of a carbon atom is also helpful for epoxides (11) without carbonyl substituents. The reagent should be a nucleophilic carbene equivalent and a sulphur ylid (12) is the answer.These can be made from the sulphide (13) by a similar process to phosphorus ylid synthesis (Chapter 15), though the reactions of the two ylids with carbonyl compounds are significantly different (there is a third type of reaction with the ylid CH2N2 in Chapter 31). 

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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