摘要:
Abstract[2+2] cycloaddition reactions of isothiazoles with diphenyl ketene afford new fused β‐lactam systems. The intramolecular nucleophilic attack of carbanions on isothiazolium salts is found to take place on the ring sulphur atom. 2‐H‐2‐benzoyl‐1, 3‐thiazines were prepared and allowed to react with diphenyl ketene, or with acid chloride in the presence of a tertiary amine, to afford the corresponding β‐lactams.