tert-Butyl[1-(3,4-dichlorophenyl)-1-methylaminomethyl-3-butenyl]methylcarbamate (500 mg) produced in Example 4 was dissolved in methylene chloride (10 mL). Under cooling with ice, pyridine (163 μL) and chlorodifluoroacetic acid anhydride (350 μL) were added thereto. Under cooling with ice, the mixture was stirred for 50 minutes. Saturated aqueous sodium bicarbonate was added to the reaction mixture, and the resultant mixture was extracted with methylene chloride. The organic layer was washed with saturated brine, dried over sodium sulfate anhydrate, and concentrated under reduced pressure. The residue was purified through silica gel column chromatography (n-hexane:ethyl acetate=4:1), to thereby give the title compound (300 mg, 46%).
