P(Cl)(Cl)([Cl:3])=O.[CH3:6][N:7]([CH3:10])C=O.[F:11][CH:12]([F:20])[C:13]1[CH:17]=[C:16]([OH:18])N(C)[N:14]=1>O>[Cl:3][C:10]1[N:7]([CH3:6])[N:14]=[C:13]([CH:12]([F:20])[F:11])[C:17]=1[CH:16]=[O:18]41.6 g (270.1 mmoles) of phosphorus oxychloride was added, with ice-cooling, to 7.9 g (108.0 mmoles) of N,N-dimethylformamide. Thereto was added, at room temperature, 8.0 g (54.0 mmoles) of 3-difluoromethyl-1-methyl-1H-pyrazol-5-ol. The mixture was refluxed for 4 hours with heating, to give rise to a reaction. After the completion of the reaction, the reaction mixture was poured into water, followed by extraction with chloroform. The resulting organic layer was washed with water, a 5% aqueous sodium hydroxide solution and water in this order and then dried over anhydrous magnesium sulfate. The resulting solution was subjected to vacuum distillation to remove the solvent contained therein. The residue was purified by silica gel column chromatography (developing solvent: hexane-ethyl acetate mixed solvent) to obtain 7.7 g (yield: 73.3%) of 5-chloro-3-difluoromethyl-1-methyl-1H-pyrazole-4-carboaldehyde as white crystals.
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