Acetylation and acetoxylation of 4-hydroxy-1,4-benzothiazin- and -benzoxazin-3(4H)-ones (cyclic hydroxamic acids)

Abstract

Treatment of 4-hydroxy-2H-1,4-benzothiazin-3(4H)-one (Ia) and its 6-methyl derivatives (Ie) with acetyl chloride yielded 4-acetoxy-derivatives (Ib and f); however, when acetic anhydride was the acetylating agent, 2-acetoxy-lactams (Ic and g) were obtained. In contrast, only 4-acetoxy-2H-1,4-benzothiazin-3(4H)-one 1,1-dioxide (IIb) was isolated when the sulphone corresponding to (Ia) was heated with either acetyl chloride or acetic anhydride. Whereas the 4-acetoxy-lactam (IIIb) was formed by the action of acetyl chloride on 4-hydroxy-2H-1,4-benzoxazin-3(4H)-one (IIIa), treatment of this hydroxamic acid with acetic anhydride gave a mixture of the corresponding 6- and 7-acetoxy-lactams (IIIc and e). Mechanisms for the formation of these acetoxy-compounds are suggested, and some of their reactions are described.