To a mixture of 4-hydroxy-2-methyl-N-(1-oxo-2,4,6-cycloheptatrien-2-yl)-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide (2.0 g) and cinnamoyl chloride (1.3 g) in N,N-dimethylformamide (30 ml) was added pyridine (0.9 ml). The mixture was stirred at room temperature for 2.5 hours. The reaction mixture was poured into cooled water to give crystals, which were collected by filtration and washed with water. The crude crystals were dissolved in chloroform and the solution was washed successively with water and brine, dried over anhydrous magnesium sulfate, treated with activated charcoal and evaporated under reduced pressure to give crystals. The crystals were recrystallized from a mixture of ethyl acetate and hexane to give N-(1-oxo-2,4,6-cycloheptatrien-2-yl)-2-methyl-4-cinnamoyloxy-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide (2.4 g).
