Cyclopropanes from sulfur ylids

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. 

Proton removal from mixed cyclopropylisopropylphosphonium salts to form phos-phoranes gave only the products 182 resulting from proton removal from the isopropyl groupsHowever, sulfur ylids such as 183 may be prepared and have found wide application in synthesis Equilibrium acidities of cyclopropanes substituted with a variety of sulfonyl-type substituents have also been measured ... 

Double bonds adjacent to complexed dienes can be cyclopropanated using diazomethane, methyl diazoacetate, or sulfur-based ylids. Cycloheptatriene iron tricarbonyl undergo a [2 -F 2] cycloaddition with chloroketene derived from trichloroacetyl chloride (Scheme 161). 

The ylid forms in the usual way but can t reach across the ring to attack the carbonyl group so it has to do conjugate addition instead. It also has to attack from the top face as it is teth -- there. Completion of the cyclopropane-forming reaction leaves the sulfur still attached to fc angular methyl group, from which it is freed by Raney nickel. This reaction shows that si— sulfonium ylids can do conjugate addition - they just prefer not to. 

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