[Synthesis of 2,3-diazaphenothiazine. XI. 2- and 3-arylderivatives of 10-methyl-2,3-dihydropyridazine /4,5-b/ / 1,4/ benzothiazin-1,4(10H)-dione].

The synthesis of 3-phenyl-10-methyl-2,3-dihydropyridazine[4,5-b] [1,4]benzothiazin-1,4(10H)-dione (I) and the 2 phenyl siomer-(II) is described. The compounds were prepared by the reaction of 2-methylaminothiophenol with 1,2-dihydro-20phenyl-4,5-dibromopyridazin-3,6-dione in an alkaline aqueous/alcoholic medium. The structure of the two isomers was demonstrated by transformation of (I) into 3-phenyl-10-methyl-3H-pyridazino[4,5-b] [1,4]benzothiazin-4(10H)-one (IV) reported in the literature.