Diisopropyl dithiolanylidenemalonate (isoprothiolane) was oxidized with m-chloroperbenzoic acid to give a monosulfoxide, disulfoxide, and disulfone. The monosulfoxide was subjected to addition reactions with such nucleophiles as methanol, thiols, and amines at the thioacetal carbon to open the dithiolane ring, affording a thiosulfinate, sulfinate and disulfide. The presence of a small amount of sodium carbonate accelerated the reactions and, moreover, reformed isoprothiolane from the ring-opened addition products. The further oxidation products were transformed into dithianes by reacting with nucleophiles. Isoprothiolane monosulfoxide inhibited alcohol dehydrogenase, an SH enzyme.