Ring Expansion of N-Aminobenzothiazolium Salts to Benzothiazines and Benzothiadiazines

摘要

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 conjuga-tive nature of the aldehyde used.As mentioned in one of our recent publication,very limited information is known concerning the chemistry of N-aminobenzothiazolium salts. Three decades ago,Tamu-ra and his co-workers described that treatment of N-ami-no-2-methylbenzothiazolium mesylate (1) with aldehydes gives rise to a [l,3,4]benzothiazine derivative (2).