Ring transformation of 5‐aroyl‐3(2 H )‐isothiazolones to 1,2,5‐oxathiazole and 1,2,3‐thiadiazole derivatives

Reaction of 2‐substituted‐5‐aroyl‐3(2 H )‐isothiazolones 2 with hydroxylamine and phenylhydrazine was found to give ( N ‐substituted‐carboxamido)methylene derivatives of 1,2,5‐oxathiazole and 1,2,3‐thiadiazole, 5 and 7 , respectively. The formation of these heterocycles was ascribed to a mononuclear heterocyclic rear‐rangement of the initially formed ketone derivatives, oximes and hydrazones, through a nucleophilic attack of the = N‐OH and = N‐NH‐ groups on the SN bond of the isothiazolone ring. In a similar manner, reaction of isothiazolones 2 with hydrazine was found to give 4‐aryl‐5‐( N ‐substituted‐carboxamido)methyl‐1,2,3‐thiadiazoles 17 .