An amount (1.1 g) of 5-fluoro-4-fluoromethyl-4-(4-trifluoromethylphenoxy)-2-pentynoic acid and triethylamine (903 mg) were dissolved in dichloromethane (20 ml); to the solution under stirring at −10° C., ethyl chloroformate (464 mg) was added dropwise and the mixture was stirred at −10° C. for another one hour. Subsequently, 3-aminopropionitrile (500 mg) was added to the reaction mixture, followed by stirring at room temperature for 2 hours. To the reaction mixture, a hexane/ethyl acetate mixed solvent (1/1) was added and the resulting mixture was washed with 0.1 N HCl, a saturated aqueous solution of sodium hydrogencarbonate and a saturated aqueous solution of sodium chloride, dried with anhydrous sodium sulfate and concentrated under reduced pressure; the resulting residue was subjected to silica gel column chromatography (eluent; hexane/ethyl acetate=3/2) to give the titled compound (1.2 g) as a colorless oil.
