[CH3:1][C:2]1[N:7]([C:8]2[CH:13]=[CH:12][CH:11]=[C:10]([C:14]([F:17])([F:16])[F:15])[CH:9]=2)[C:6](=[O:18])[C:5](=O)[NH:4][CH:3]=1.C(Br)(=O)C([Br:23])=O>CN(C=O)C.ClCCCl>[Br:23][C:5]1[C:6](=[O:18])[N:7]([C:8]2[CH:13]=[CH:12][CH:11]=[C:10]([C:14]([F:17])([F:16])[F:15])[CH:9]=2)[C:2]([CH3:1])=[CH:3][N:4]=16-Methyl-1-[3-(trifluoromethyl)phenyl]-1,4-dihydropyrazine-2,3-dione (0.52 g, 1.92 mmol) and 1,2-dichloroethane (10 ml) were placed in a vial (20 ml). To the resulting suspension was added carefully oxalyl bromide (0.53 ml, 1.24 g, 5.75 mmol). A foam was formed during the addition, and as the foam was settling down the stirring was started. DMF (3 drops) was added and the vial was sealed and the mixture was stirred overnight. Another portion of oxalyl bromide (0.2 ml, 0.46 g, 2.23 mmol) and DMF (3 drops) was added and the reaction was run for another 24 h. The mixture was partitioned between is DCM (20 ml) and water (20 ml) and the organic phase was dried. Filtration and evaporation gave a crude product, which was purified on silica, affording 3-bromo-6-methyl-1-[3-(trifluoromethyl)phenyl]pyrazin-2(1H)-one (0.59 g, 93%).
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