Hydrochloric Acid → 3,4-dihydro-2-methyl-3-oxo-2H-1,2-benzothiazine-4-carboxylic acid 1,1-dioxide

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Reaction Steps

In a four neck flask equipped with reflux condenser, stirrer, thermometer and calcium drying tube, 1.06 g (0.005 mole) 3,4-dihydro-2-methyl-3-oxo-2H-1,2-benzothiazine 1,1-dioxide and 2.6 g (0.02 mole) methylmagnesiumcarbonate in 20 ml N,N-dimethylformamide were added. The mixture was stirred at 90°-100° C. for 3 hours. The resulting solution was poured quickly into a mixture of 30 ml conc-hydrochloric acid, 70 g ice chips and 200 ml diethylether. After stirring the mixture for 10 minutes, the separated diethylether layer was evaporated in vacuo to obtain 1.25 g of 3,4-dihydro-2-methyl-3-oxo-2H-1,2-benzothiazine-4-carboxylic acid 1,1-dioxide. The obtained compound was dissolved in 20 ml benzene and to the solution, 1.3 ml thionyl chloride and 0.4 ml N,N-dimethylformamide were added.

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