Application of directed metalation in synthesis. Part 6: A novel anionic rearrangement under directed metalation conditions leading to heteroannulation

A short and efficient synthesis of condensed 1,4-oxathiin-2-ones from easily available phenols is described. The key step in this synthesis is a hitherto unreported anionic rearrangement under directed metalation conditions. The rearrangement occurs after side chain deprotonation of a methyl sulfanyl group by an O-carbamate directed metalating group and the reaction mixture is kept at room temperature for 8-12 h. Acid-mediated cyclisation of the rearranged product affords [1,4]oxathiin-2-one.