While a dimethylformamide suspension containing 0.17 g of 60% sodium hydride was being cooled with ice, 10 ml of a dimethylformamide solution containing 1.00 g of 3-amino-5-(4-fluorophenyl)-4-(4-pyridyl)pyrazole was added dropwise thereto, followed by stirring at room temperature for 30 minutes. Then, 5 ml of a dimethylformamide solution containing 0.67 g of methyl iodide was added dropwise thereto, followed by stirring at room temperature for 3 hours. After the dimethylformamide was distilled off under reduced pressure, the resulting residue was extracted with chloroform. The organic layer was washed with water and dried over anhydrous magnesium sulfate. After the solvent was distilled off under reduced pressure, the resulting residue was purified by column chromatography using 250 g of silica gel [with an elution solvent comprising chloroform-methanol (20:1)]. Thus, 0.34 g (32% yield) of 3-amino-5-(4-fluorophenyl)-1-methyl-4-(4-pyridyl)pyrazole (light-brown crystals) was obtained as a first elution product, and 0.45 g (43% yield) of 5-amino-3-(4-fluorophenyl)-1-methyl-4-(4-pyridyl)pyrazole (light-brown crystals) as a second elution product.
