C[O:2][C:3](=[O:19])[C:4]1[C:5](=[C:10]([CH3:18])[C:11]([NH2:17])=[C:12]([N+:14]([O-:16])=[O:15])[CH:13]=1)[C:6]([O:8][CH3:9])=[O:7].[OH-].[Na+].Cl>C1COCC1.O>[CH3:9][O:8][C:6](=[O:7])[C:5]1[C:4](=[CH:13][C:12]([N+:14]([O-:16])=[O:15])=[C:11]([NH2:17])[C:10]=1[CH3:18])[C:3]([OH:19])=[O:2]To a solution of 4-Amino-3-methyl-5-nitro-phthalic acid dimethyl ester (1.8 g, 6.72 mmol) in THF (10 mL) and water (20 mL) was added 5 N NaOH (4.0 mL) and the resulting mixture was stirred at room temperature for 24 h. The reaction mixture was acidified with conc. HCl (pH=2.0) and extracted with EtOAc (2×100 mL). The combined organic layer was dried over Na2SO4, filtered and concentrated in vacuo to afford the 4-Amino-3-methyl-5-nitro-phthalic acid 2-methyl ester (1.3 g, 76%) as a yellow solid.
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