3,4-Dihydro-3-oxo-2H-benzo[b][1,4]thiazine-6-carboxylic acid

204863-53-6

272437-84-0

The general procedure for the synthesis of 3-oxo-3,4-dihydro-2H-1,4-benzothiazine-6-carboxylic acid from ethyl 3-oxo-4H-1,4-benzothiazine-6-carboxylate was as follows: to a solution of tetrahydrofuran (THF, 30 mL) of ethyl 3-oxo-3,4-dihydro-2H-1,4-benzothiazine-6-carboxylate (5.1 g, 21 mmol), 1 N aqueous sodium hydroxide solution (100 mL). The reaction mixture was stirred at room temperature for 3 hours. Upon completion of the reaction, the reaction solution was acidified with 1 N hydrochloric acid and subsequently extracted with ethyl acetate. The organic phases were combined, washed with saturated aqueous sodium chloride solution, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The resulting residue was recrystallized with diisopropyl ether to give the title compound as white crystals (3.65 g, 83% yield).1H NMR (300 MHz, DMSO-d6) δ: 3.26 (br, 1H), 3.48 (s, 2H), 7.34-7.51 (m, 3H), 10.69 (br, 1H).