The synthesis and reactions of 4H-tetrazolo[5,1-c][1,4]benzothiazines

Abstract

The synthesis of 4H-tetrazolo[5,1-c][1,4]benzothiazines via an intramolecular dipolar addition reaction of 2-(2-azidophenylthio)acetonitrile is described. The methylene protons of the thiazine ring were found to be sufficiently acidic to be readily functionalised by base-catalysed deprotonation followed by reaction with electrophiles (e.g. alkyl halides). N-Bromosuccinimide also reacted at this position to give 4-bromo-4H-tetrazolo[5,1-c][1,4]benzothiazine whilst bromination of 4-methyl-4H-tetrazolo[5,1-c][1,4]benzothiazine gave 4-bromomethylene-4H-tetrazolo[5,1-c][1,4]benzothiazine. This material reacted with alkoxides to give unusually acid-stable acetals.