[H-].[Na+].[CH2:3]([O:5][C:6]([C:8]1[CH:9]=[N:10][N:11]([C:14]2[CH:19]=[CH:18][C:17]([OH:20])=[CH:16][CH:15]=2)[C:12]=1[CH3:13])=[O:7])[CH3:4].[CH2:21](I)[CH3:22].O>CN(C)C=O>[CH2:3]([O:5][C:6]([C:8]1[CH:9]=[N:10][N:11]([C:14]2[CH:15]=[CH:16][C:17]([O:20][CH2:21][CH3:22])=[CH:18][CH:19]=2)[C:12]=1[CH3:13])=[O:7])[CH3:4]Sodium hydride (234 mg) was added to a solution of 1-(4-hydroxyphenyl)-5-methyl-1H-pyrazole-4-carboxylic acid ethyl ester (1.2 g) in N,N-dimethylformamide (12 ml) at room temperature, stirred at the same temperature for 30 minutes, then ethyl iodide (0.8 ml) was added therein and the mixture was stirred at 80° C. for an hour. After completion of the reaction, the reaction solution was cooled to room temperature, water was added therein and extracted with ethyl acetate three times. The organic layer was dried over anhydrous sodium sulfate and concentrated. The resulting residue was purified with silica gel column chromatography (n-hexane/ethyl acetate) to give 1-(4-ethoxyphenyl)-5-methyl-1H-pyrazole-4-carboxylic acid ethyl ester (1.32 g) as a white solid.
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