[F:1][C:2]([F:11])([F:10])[C:3]1[CH2:4][CH2:5][C:6](=[O:9])[NH:7][N:8]=1.BrBr>C(O)(=O)C>[F:11][C:2]([F:1])([F:10])[C:3]1[CH:4]=[CH:5][C:6](=[O:9])[NH:7][N:8]=12.6 g (15.65 mmol) of 6-(trifluoromethyl)-4,5-dihydropyridazin-3(2H)-one were dissolved in 20 ml of glacial acetic acid, and the mixture was heated to 100° C. 0.81 ml (15.65 mmol) of bromine was then slowly added dropwise to the solution, and the mixture was stirred at 100° C. for 4 hours. After cooling of the reaction solution, the solvent was removed under reduced pressure and the residue obtained was purified chromatographically on silica gel (mobile phase dichloromethane/methanol 50:1→20:1). This gave 1.34 g (8.15 mmol, 52% of theory) of the title compound.
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