1,4-Benzothiazineに関する研究(第3報)2-Acyl-4-methylbenzothiazine類およびその関連化合物の反応性

Abstract

It has been found that 2-acyl-4-alkyl-4H-1, 4-thiazine derivatives (1a-f) were oxidized to their sulfoxides (2a-f) by treatment with sodium nitrite in acetic acid under mild conditions. However, this reaction was unable to be applied to thiazine derivatives such as 3a, 3b, and 4, lacking an acyl group at the 2-position and 2-acylthiophens being partially analogous with 2-acylthiazine. Alkali treatment of the sulfoxides (2a and 2b) gave 3, 4-dimethyl-4H-1, 4-benzothiazine-1-oxide (9a) and 4-methyl-3-phenyl-4H-1, 4-benzothiazine-1-oxide (9b), respectively. The fact that 3-hydroxy-2, 3-dihydro-4H-1, 4-benzothiazine derivative (8b) was isolated as an intermediate in transformation from 2b to 9b suggests that 9a and 9b may be formed via the reaction process shown in Chart 2. When 9b was treated with acid such as hydrochloric acid or p-toluenesulfonic acid, reductive dimerization of 9b proceeded to give benzothiazinylbenzothiazine derivative (14) in poor yield (below 15%), while the acid treatment of an equimolecular mixture of 9b and 3a elevated the yield from 14 to 64%. From these observations, it was suggested that the process from 9b to 14 might be as shown in Chart 3. Finally, Pummerer reaction of 9b with acetic anhydride was examined.