[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[C:9](=[O:18])[NH:10][C:11]([C:14]([F:17])([F:16])[F:15])=[CH:12][N:13]=2)=[C:4]([F:19])[CH:3]=1.[C:20](=O)([O-])[O-].[K+].[K+].CI.O>CN(C)C=O>[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[C:9](=[O:18])[N:10]([CH3:20])[C:11]([C:14]([F:17])([F:15])[F:16])=[CH:12][N:13]=2)=[C:4]([F:19])[CH:3]=1First, 2.93 g of 3-(4-chloro-2-fluorophenyl)-6-trifluoromethyl-2-oxo-1,2-dihydropyrazine (compound 1-1005) was dissolved in 15 ml of N,N-dimethylformamide, to which 2.07 g of potassium carbonate and 1.25 ml of methyl iodide were added, and the mixture was stirred at 100° C. for 2 days. After completion of the reaction, the reaction mixture was poured into water, followed by extraction with ethyl acetate. The organic layer was washed with saturated sodium chloride solution, dried with anhydrous magnesium sulfate, and concentrated. The residue was subjected to silica gel column chromatography (eluent, hexane/ethyl acetate=6:1), which afforded 1.98 g (yield, 65%) of 3-(4-chloro-2-fluorophenyl)-1-methyl-6-trifluoromethyl-2-oxo-1,2-dihydropyrazine (present compound 1-11; m.p., 83.2° C.).
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