Influence of ring size on the outcome of sulfide contraction reactions with thiolactams. Isolartion of bicyclic ketene S,N-acetals and thioisomunchnones

摘要

Reaction between diethyl bromomalonate and 3-phenylpyrrolidine-2-thione yielded a vinylogous urethane by the Eschenmoser sulfide contraction. However, with 3-substituted piperidine-2-thiones, sulfur was retained in the productrs, and a range of bicyclic heterocycles, including bicyclic ketene S,N-acetals (2-alkylidene-1,3-thiazolidin-4-ones) and stable thioisomunchnones, was isolated. A novel dimeric ketene S,N-acetal was characterised by X-ray crytallography.