[OH-:1].[K+].[Cl:3][C:4]1[C:9]([Cl:10])=[CH:8][C:7]([C:11]([F:14])([F:13])[F:12])=[C:6]([Cl:15])[N:5]=1.Cl>C(O)(C)(C)C>[Cl:10][C:9]1[C:4](=[O:1])[NH:5][C:6]([Cl:15])=[C:7]([C:11]([F:14])([F:13])[F:12])[CH:8]=1.[Cl:10][C:9]1[CH:8]=[C:7]([C:11]([F:14])([F:13])[F:12])[C:6](=[O:1])[NH:5][C:4]=1[Cl:3]To a solution of 2.7 g of potassium hydroxide dissolved in 37 ml of t-butanol was added 6.0 g of 2,3,6-trichloro-5-trifluoromethylpyridine, and the solution was reacted at 80° C. for 3 hours while stirring. After completion of the reaction, the reaction product was allowed to cool and made acidic with concentrated hydrochloric acid. The solvent was distilled off under reduced pressure, and the residue was extracted with methylene chloride. The methylene chloride solution was washed with water and dried over anhydrous sodium sulfate. The methylene chloride was distilled off under reduced pressure, and the resulting residue was passed through a silica gel column (eluent: an n-hexane-ethyl acetate (3:1 by weight) mixture) to obtain 1.5 g of 3,6-dichloro-5-trifluoromethyl-2-pyridone having a melting point of 129° to 131° C. and 0.8 g of 5,6-dichloro-3-trifluoromethyl-2-pyridone having a melting point of 163° to 165° C., respectively.
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