[Cl:1][C:2]1[C:3]([Cl:19])=[CH:4][C:5]2[O:10][CH2:9][C:8](=[O:11])[N:7]([CH2:12][C:13]([O:15]CC)=[O:14])[C:6]=2[CH:18]=1.[Li+].[OH-].O.Cl>C1COCC1.C(O)(=O)C>[Cl:1][C:2]1[C:3]([Cl:19])=[CH:4][C:5]2[O:10][CH2:9][C:8](=[O:11])[N:7]([CH2:12][C:13]([OH:15])=[O:14])[C:6]=2[CH:18]=1Ethyl (6,7-dichloro-3-oxo-2,3-dihydro-4H-1,4-benzoxazin-4-yl)acetate (52.6 g, 0.173 mol) and LiOH (8.31 g, 0.347 mol) were combined in 750 mL of THF and 150 mL of water and stirred at room temperature for 18 hours, after which time HPLC indicated loss of the starting material. 80 mL of concentrated HCl was added and the mixture was stirred for 1 hour, and then evaporated to dryness. The residue was dissolved in EtOAc and water was added. The layers were separated and the organic layer was washed with water (2×). The organic layer was dried over magnesium sulphate and concentrated to give 45.5 g (0.165 mol, 95%) of 6,7-dichloro-3-oxo-2,3-dihydro-4H-1,4-benzoxazin-4-yl)acetic acid. MS (ES) m/e 278 [M+H]+.
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