Reaction of 2, 2′-dithiodianiline with 2-alkyl-1, 3-diketones. Synthesis and chemical behaviour of some 2-acyl-2h-1, 4-benzothiazines

The reactions of 2, 2′-dithiodianiline 1 with 2-alkyl-1, 3-diketones 2a-d have been employed in order to synthesize 2-acyl-2H-1, 4-benzothiazines. In the cases of 2a, b the expected 2-acyl-2H-1, 4-benzothiazines, i.e. 3a, b were obtained, whereas the reactions of 1 with the 1, 3-diketones 2c, d afforded the α-ketosulfide 12 and the 1, 4-benzothiazine 17 , respectively. The products 3a, b underwent the hydrolytic C₂-C₃ bond cleavage of the thiazine nucleus to give the α-ketosulfides 6 and 11 , respectively. Such an hydrolytic process explains the formation of the compound 12 in the reaction of 1 with 2c . The formation of 17 in the case of 2d is considered to be formed through a rearrangement involving the 1, 3-sulfur shift of the preformed 1, 4-benzothiazine 3d .