Ring Expansion of N-Aminobenzothiazolium Salts to Benzothiazines and Benzothiadiazines

N-amino-2-benzylbenzothiazinium salts when reacted with aldehydes were found to undergo ring expansion reactions to give either benzothiadiazines or benzothiazines. This ambident reactivity was found to be influenced by the conjugative nature of the aldehyde used.