Generation of Sulfur Ylides from Sulfonium Salts and Their Reactions. Comparative Study of Electrochemical Reduction with the Base Method and Mechanism Elucidation by the MO Method

The cathodic reduction of sulfonium salts in acetonitrile in the presence and absence of benzaldehyde was carried out. Results were compared with results of the base method. In the presence of benzaldehyde, the electrochemical reduction gave epoxides as a result of the Corey-Chaykovsky reaction, thus confirming ylide formation. The electrochemical reduction of sulfonium salts without benzaldehyde yielded rearrangement products in high yield. On the contrary, upon base treatment of sulfonium salts without benzaldehyde, symmetrical epoxides derived from the benzyl group of the sulfonium salt are obtained as main products as a result of the auto oxidation of the sulfur ylide. The reaction mechanisms were elucidated based on the results obtained by a semi-empirical molecular orbital method.