Episulfones. III. Reductive Cleavage of Episulfones by Complex Metal Hydrides

Abstract

Abstract The reduction of cis-stilbene episulfone (I) by such a complex metal hydride as lithium borohydride, sodium borohydride, or lithium aluminum hydride gave dibenzylsulfone (V) selectively as a result of the unusual cleavage of the carbon-carbon single bond. Comparing the difference between lithium aluminum hydride and lithium borohydride or sodium borohydride in various solvent systems, we suggest that particular solvent effects are operating in the present reaction. The reduction of I with lithium aluminum hydride resulted in a low yield (0–10%) of V, while the reduction with lithium borohydride afforded V in a 45% yield. The reduction of styrene episulfone (II) gave no carbon-carbon cleavage product, but it did give a carbon-sulfur fission product, yielding sulfinic acid salt (VIII). The formation of VIII is interesting compared with the reduction of styrene oxide by lithium aluminum hydride. Tetraphenylethylene episulfone (III) produced a carbon-carbon cleavage product, 1, 1, 3, 3-tetraphenyl dimethyl sulfone (XI), in a 68% yield. A reaction mechanism for the reductive cleavage reaction has been proposed on the basis of the above-mentioned results. In addition, we observed that diborane was evolved by the reaction of sulfur dioxide with lithium- or sodium borohydrides.