C([O:3][C:4]([C:6]1[NH:7][C:8]([CH:12]=[O:13])=[C:9]([CH3:11])[CH:10]=1)=[O:5])C.[OH-].[K+]>O.C(O)C>[CH:12]([C:8]1[NH:7][C:6]([C:4]([OH:5])=[O:3])=[CH:10][C:9]=1[CH3:11])=[O:13]To a solution of 0.8 g (4.4 mmol) of 5-formyl-4-methyl-1H-pyrrole-2-carboxylic acid ethyl ester in 35 mL of water and 15 mL of ethanol was added 0.5 g (8.9 mmol) of potassium hydroxide. The reaction mixture was heated to 100 ° C. for 1 hour, cooled to room temperature, and evaporated ethanol. The water layer was acidified to pH=3 using 2N hydrogen chloride solution. The precipitate was filtered and washed with water to afford 0.67 g (68%) of 5-formyl-4-methyl-1H-pyrrole-2-carboxylic acid as a tan solid. 1H NMR (360 MHz, DMSO-d6) δ 12.92 (br s, 1H, CO2H), 12.48 (br s, 1H, NH), 9.76 (s, 1H, CHO-5), 6.63 (s, 1H), 2.28 (s, 3H, CH3). MS m/z 152 [M−1].
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