Sulfonium Ylides. Application to the Synthesis of Optically Active Epoxides

Abstract

The transfer of benzylidene groups from S-benzylsulfonium salts obtained from several optically active thiolanes and thianes to aldehydes and ketones yields optically active epoxides with high enatiomeric purity. In contrast, methylene transfer via the same auxiliaries leads to inactive epoxides. It is proposed that the difference in behaviour between these systems is best explained by assuming a 2+2 cycloaddition mechanism rather than the more commonly proposed nucleophilic anti-periplanar addition for the reaction of a sulfur ylide with a carbonyl component.