[OH-].[Na+].[CH3:3][C:4]([NH:12][C:13]1[C:18]2[CH:19]=[CH:20][CH:21]=[CH:22][C:17]=2[C:16](=[O:23])[O:15][N:14]=1)([CH:9]([CH3:11])[CH3:10])[C:5]([O:7]C)=O.[O:24]1CCCC1.S(=O)(=O)(O)O>O.C(Cl)Cl>[OH:15][N:14]1[C:5](=[O:7])[C:4]([CH:9]([CH3:11])[CH3:10])([CH3:3])[N:12]=[C:13]1[C:18]1[CH:19]=[CH:20][CH:21]=[CH:22][C:17]=1[C:16]([OH:23])=[O:24]Sodium hydroxide (0.58 g, 0.0145 mol) in water is added to a solution of methyl 2,3-dimethyl-2-[(1-oxo-2,3-benzoxazin-4-yl)amino]butyrate (2.0 g, 0.00689 mol) and tetrahydrofuran under a nitrogen atmosphere. The reaction mixture is stirred at 45° C. for 36 hours then at room temperature for 6 days. The reaction mixture is concentrated in vacuo to give an oil. The oil is dissolved into water. The aqueous solution is cooled with an ice-bath and concentrated sulfuric acid is added until a pH of about 1 is obtained then the solution is extracted with ethyl acetate. The combined ethyl acetate extracts are dried with anhydrous magnesium sulfate and concentrated in vacuo to give a pale yellow solid. The solid is added to boiling methylene chloride and after 2/3 of the methylene chloride has evaporated, the mixture is filtered to give the title compound as a white solid (1.44 g, 76%), mp 186°-188° C., identified by IR and NMR spectral analyses.
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