[CH3:1][O:2][C:3]1[CH:8]=[C:7]([C:9]([O:11]C)=[O:10])[CH:6]=[CH:5][C:4]=1[C:13]([O:15][CH3:16])=[O:14].O.[OH-].[Na+].Cl>C1COCC1>[CH3:16][O:15][C:13]([C:4]1[CH:5]=[CH:6][C:7]([C:9]([OH:11])=[O:10])=[CH:8][C:3]=1[O:2][CH3:1])=[O:14]2-Methoxy-1,4-bis (methoxycarbonyl)benzene (1.61 g, 7.20 mmol) from Step 2 was dissolved in 20 mL of 1:1 THF:H2O and to the stirred solution was added 1N NaOH (7.2 mL, 7.2 mmol). After 24 h, the reaction was acidified to pH 2 with 1N HCl. The reaction was concentrated under reduced pressure and then extracted with CHCl3. The CHCl3 layer was dried (MgSO4), filtered and evaporated under reduced pressure. The residue was purified by pressurized silica gel column chromatography using 93:7 CHCl3 :A, where A=95:5 MeOH:HOAc. 1-Methoxycarbonyl-2-methoxybenzene 4-carboxylic acid was obtained as an oil (30% yield).
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