To a solution of 2.00 g of 1-(3-bromo-4-methylphenyl)-3-(3,5-dichlorophenyl)-4,4,4-trifluoro-2-butene-1-one in 15 mL of 1,2-dichloroethane, 0.98 g of N-bromosuccinimide and 0.06 g of α,α′-azobisisobutyronitrile were added, and the resultant reaction mixture was stirred while heating the reaction mixture to reflux for 1 hour. Next, to the reaction mixture, 0.61 g of N-bromosuccinimide and 0.05 g of α,α′-azobisisobutyronitrile were added and the reaction mixture was continued to be stirred at the same temperature further for 2 hours. After the completion of the reaction, the reaction mixture was left to be cooled down to room temperature and was diluted with 50 mL of chloroform. Subsequently, the diluted reaction mixture was washed with water (30 mL×2) and then dehydrated and dried over a saturated brine and anhydrous sodium sulfate in this order, and the solvent was distilled off under reduced pressure. The resultant residue was dissolved in 10 mL of N,N-dimethylformamide, and 0.85 g of phthalimide potassium was added to the resultant solution, followed by stirring the resultant reaction mixture at room temperature for 13 hours. After the completion of the reaction, 30 mL of water was added to the reaction mixture and the resultant reaction mixture was extracted with ethyl acetate (50 mL×1). The organic phase was dehydrated and dried over a saturated brine and anhydrous magnesium sulfate in this order and the solvent was distilled off under reduced pressure. The resultant residue was purified by silica gel column chromatography eluting with ethyl acetate-hexane (1:1) to obtain 1.67 g of the objective substance as a yellow crystal.
