Lithium Hydroxide → 3-Oxo-3,4-dihydro-2H-1,4-benzoxazine-6-carboxylic acid

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To a solution of 3-oxo-3,4-dihydro-2H-benzo[1,4]oxazine-6-carboxylic acid methyl ester (3.13 g, 15.1 mmol) in THF/H2O (3:1; 76 mL) was added a LiOH (4 M in H2O; 19.0 mL, 75.5 mmol), and the solution was stirred at RT for 24 h. The solution was concentrated, diluted with H2O (50 mL), and acidified to pH<1 with conc. HCl. The resulting precipitate was collected by filtration afforded 7.6 g of the title compound contaminated with excess HCl and H2O. MS (ESI): exact mass calculated for C9H7NO4, 193.04; m/z found, 194.2 [M+H]+. 1H NMR (500 MHz, DMSO-d6): 10.85 (br s, 1H), 7.50-7.47 (m, 2H), 6.99 (d, J=8.3, 1H), 4.63 (s, 2H).

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