New features in the intramolecular capture of nitrile imines by the sulphide function

Abstract

o-Alkenylthio and o-alkynylthio substituted arylhydrazonyl chlorides (2) and (9) react with triethylamine in acetonitrile at room temperature to give 3H-4,1,2-benzothiadiazines (6) and (13) as a result of intramolecular attack of the sulphur on the intermediate nitrite imines (3) and (10) followed by a 2,3-sigmatropic shift in the resulting ylides (5) and (12). The reaction leading from the nitrile imine intermediates to benzothiadiazines is reversed on heating, allowing formation of intramolecular 1,3-dipolar cycloadducts (4) and (11) as the thermodynamic products. In one case, (13b), a novel diazetobenzothiazine (14) is formed.