Studies on 1, 4-Benzothiazines. IV. Reactions of 2-Acyl-4H-1, 4-benzothiazines with Hydroxylamine, Hydrazine, Guanidine and Acetamidine

2-Acyl-4-methyl-4H-1, 4-benzothiazines (1a, b) reacted with hydroxylamine to give dihydroisoxazolo [4, 5-b] [1, 4] benzothiazines (3a, b). However, the reaction of 1a with hydrazine did not give the dihydropyrazolo [4, 5-b] [1, 4] benzothiazine derivative corresponding to 3a, but gave its dehydro compound (6). On the other hand, in the reaction of 1b with hydrazine, formation of a pyrazole ring and opening of the thiazine ring occurred to afford a 4-(2-aminophenylthio) pyrazole derivative (7). Guanidine and acetamidine also reacted with 1a, b to give 5-[2-(N-methylamino) phenylthio] pyrimidines (10a-d).