Synthesis of some new tricyclic 1,4-benzothiazinones

2-Aminothiophenol on reaction with dimethyl oxalate and methyl 2-chloropropionate gives 1,4-benzothiazinone (la, 1b) which when reacted with ethyl chloroacetate give N-ethoxycarbonylmethyl-1,4-benzothiazine-2,3-diene (2a 1 ). Compound 2 on reaction with hydrazine hydrate affords N-hydrazidomethyl-1,4-benzothiazine-2,3-dione (3). Compound 3 is cyclized in presence of ammonium acetate and acetic acid to give 5-methyl[1,2,4]triazino-6-oxo[3,4-c]-3(1H)-[1,4]benzothiazine (4b 1 ). Compound 1 on reaction with phosphorus oxychloride gives 3-chloro-1,4-benzothiazine-3-one (5a) which when reacts with ammonium sulfocyanide affords 1,4-benzothiazin-2-one-3-ylisocyanate (6a). Compound 6 when reacted with methyl cyanide gives the desired tricyclic compound 2-thio-6-methyl[1,3,5]triazolo[3,4-c]benzothiazine-2-one (7a).