Synthesis and structural characterisation of 4H-1,3-benzothiazine derivatives

The ring-closure reactions of N-arylthiomethylaroylamide derivatives (1a-g) in the presence of phosphorus oxychloride gave 2-aryl-4H-1,3-benzo-thiazines (2a-g). 2-(3-Chlorophenyl)-6-methyl-4H-1,3-benzothiazine (2b) was reduced with Zn to obtain the corresponding 2,3-dihydro derivative (3b). Potassium permanganate oxidation of 2-(4-chlorophenyl)-2,3-diethoxy-4H- (2e) and 2-(2-fluorophenyl)-6,7-diethoxy-4H-1,3-benzo-thiazines (2g) gave the corresponding 4-ones-(4e,g). The reactions of 2-(4-chlorophenyl)-6methyl-4H-1,3-benzothiazine (2c) with substituted acetyl chlorides led to linearly condensed beta-lactams (5a,b). The structures of the compounds studied were confirmed by H-1 and C-13 NMR and by their characteristic mass spectrometric fragmentations.