[CH:1]([C:3]1[N:7]([CH3:8])[CH:6]=[C:5]([C:9]([O:11]C)=[O:10])[CH:4]=1)=[O:2].[CH3:13]O.[OH-].[Na+]>O>[CH3:13][C:6]1[N:7]([CH3:8])[C:3]([CH:1]=[O:2])=[CH:4][C:5]=1[C:9]([OH:11])=[O:10]To a solution of methyl 5-formyl-1-methyl-1H-pyrrole-3-carboxylate (90.0 g, 0.540 mol), MeOH (1000 mL) and water (500 mL) was added sodium hydroxide solution (1000 mL, 1.0 M in water). The mixture was heated at 40° C. overnight. Solvent was then evaporated, and the aqueous residue was neutralized with 1 N HCl and extracted with EtOAc (3×500 mL) to give methyl 5-formyl-1-methyl-1H-pyrrole-3-carboxylic acid (70.0 g, 85%). 1H NMR (CDCl3, 400 MHz) δ 9.54 (s, 1H), 7.45 (s, 1H), 7.32 (s, 1H), 3.93 (s, 3H).
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