Acid-Catalyzed Ring Opening Reactions of Episulfoxides

The acid-catalyzed ring opening reactions of episulfoxides in various solvents have been studied. The reaction of ethylene episulfoxide (1) in methanol in the presence of sulfuric acid produced thiol sulfinate 2a, while that of 1 in ethyl mercaptan afforded disulfide 5. The orientational effect of nucleophiles in the ring openings of unsymmetrically substituted episulfoxides, i.e., 7 and 10, were also investigated in several alcohols, ethyl mercaptan, and mixed solvents. The structural analyses of the products obtained from cis- and trans-butene episulfoxides (14 and 15) in methanol demonstrated that the reactions proceeded stereospecifically with inversion of configuration at the point of attack. These results are discussed in terms of a “push–pull” mechanism.