Reactions of enamino-ketones. Part II. Synthesis of 4H-1,4-benzothiazines

Abstract

A new synthesis of 4H-1,4-benzothiazines, consisting of the condensation of o-aminobenzenethiol with cyclohexane-1,3-diones, acetylacetone, benzoylacetone, or ethyl acetoacetate in dimethyl sulphoxide, is described. An oxidative cyclisation mechanism, involving an intramolecular nucleophilic attack in an intermediate enaminoketone, is suggested.