Preparation of 4-substituted 1,3-oxathiolan-5-onesviathe sulphenium ion intermediate generated by the pummerer rearrangement

4-Substituted 1,3-oxathiolan-5-ones have been synthesized via the Pummerer rearrangement from the S-oxide of the parent molecule. The 4,5-dione is obtained in the presence of pyridine N-oxide.