Process for the preparation of

Abstract

An improved process for the preparation of 4-hydroxy-3-(5-methyl-3-isoxazolylcarbamoyl)-2-methyl-2H-1,2-benzothiazine 1,1-dioxide (I), a known anti-inflammatory agent, requires the use of specific proportions of reactants and carefully controlled reaction conditions. An alkali metal alkoxide, suspended in dimethylformamide is combined, with stirring, as rapidly as possible with a solution of alkyl 2,3-dihydro-3-oxo-1,2-benzisothiazole-2-acetate 1,1-dioxide (II) in dimethylformamide, while maining the internal reaction temperature within 15.degree.-30.degree.C. More than two but less than six moles of the alkoxide are used per mole of the alkyl 2,3-dihydro-3-oxo-1,2-benzisothiazole-2-acetate 1,1-dioxide (II). After all reactants have been combined, stirring is continued for a specific period of time and then the reaction mixture is acidified. Total elapsed time from initial combination of reactants to acidification is from 30 to 50 minutes. Acidification of the reaction mixture precipitates out alkyl 4-hydroxy-2H-1,2-benzothiazine-3-carboxylate 1,1-dioxide (III) in substantially pure form in high yields, without recrystallization. Product III is methylated on the sulfonamide nitrogen and reacted with 3-amino-5-methyl-isoxazole to obtain crude I. A further improvement in the process of the invention involves a more efficient method for purifying crude product I: the need for large quantities of dioxane solvent is obviated. After slurrying and washing, product I is solubilized in dilute alkali, and decolorized. After filtration and acidification pure product I in high yield is obtained. In addition to preparing the known anti-inflammatory agent (I), the initial reaction step of the invention wherein 2,3-dihydro-3-oxo-1,2-benzisothiazole-2-acetate, 1,1-dioxide (II) is rearranged to form alkyl 4-hydroxy-2H-1,2-benzothiazine-3-carboxylate 1,1-dioxide (III), may be used with particular advantage for the preparation of other useful benzothiazine derivatives.