A new acid-catalysed rearrangement of thiosulphinates to α-acetylthiosulphoxides in acetic anhydride

Abstract

Some thiosulphinates with at least one proton on the carbon adjacent to the sulphenyl sulphur react with acetic anhydride containing acetic acid to afford the corresponding α-acetylthio-sulphoxides. The mechanism of this reaction was studied using thiosulphinates labelled with ²H, ¹³C, and ¹⁸O. These tracer experiments demonstrated that the reaction proceeds via an initial E_i reaction to form the corresponding sulphenic acid and thioaldehyde followed by recombination in which the sulphur atom of the sulphenic acid adds to the carbon atom of the thioaldehyde, eventually affording the rearranged α-acetylthio-sulphoxide. The formation of the sulphenic acid was confirmed by trapping it with methyl acrylate. The mechanism of the reaction is discussed.