Abstract
Reaction of simple benzothiazolium salts (V) with diethyl acylphosphonates (II) afforded ring-expanded products, 1, 4-benzothiazine derivatives (VII). In this reaction, it was found necessary to add II before triethylamine. VIIa-b were confirmed to be identical with authentic samples synthesized by the independent pathway shown in Chart 2. The reaction of 4-methylthiazolium salts (XIII) with II afforded 1 : 1 adducts (XIV), which were decomposed to corresponding 1, 4-thiazine derivatives (XV) by alkaline treatment. Treatment of 2-phenyl-3-oxo-4-benzyl-5-methyl-6-(2-acyloxy) ethyl-2, 3-dihydro-4H-1, 4-thiazine (IV) with hydrogen peroxide in acetic acid gave 2-hydroxy-2-phenyl-3-oxo-4-benzyl-5-methyl-6-(2-acyloxy) ethyl-2, 3-dihydro-4H-1, 4-thiazine (XIX).
