Pummerer rearrangements using chlorotrimethylsilane

Abstract

Attempted Pummerer rearrangement of 3-methoxycarbonylthian-4-one S-oxide in refluxing acetic anhydride gives unexpected products in which β-carbon oxidation and ring contraction has taken place. Treatment of 3-methoxycarbonylthian-4-one with N-chlorosuccinimide gives similar rearrangement products. These rearrangements are rationalised by the intermediacy of a common thiiranium ion. Chlorotrimethylsilane in refluxing tetrachloromethane efficiently effects the expected Pummerer rearrangement of 3-methoxycarbonylthian-4-one S-oxide into the corresponding α,β-unsaturated sulphides. Reactions of this reagent with related sulphoxides are also described.