Oxosulfonium ylides addition reactions

An interesting aspect of this reaction is the contrasting stereoselective behaviour of the dimethyisulfonium and dimethyloxosuifonium methylides in reactions with cyclic ketones (E.J. Corey, 1963 B, 1965 A C.E. Cook, 1968). The small, reactive dimethyisulfonium ylide prefers axial attack, but with the larger, less reactive oxosulfonium ylide only the thermodynamically favored equatorial addition is observed. 

Oxosulfonium ylides as well as sulfonium ylides stabilized by an electron-withdrawing group, such as an acyl , an alkoxycarbonyP , a cyano " and one of their vinylogues satisfactorily cyclopropanate a variety of Michael acceptors (e.g., equation 81) . In these reactions, the 1,2-addition is usually a minor pathway. Ylides stabilized by two... 

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