To a solution of 2-bromo-5-[(2,5-difluorophenyl)[(4-fluorophenyl)thio]methyl ]-4-methylpyridine (1.39 g, 3.28 mmol) obtained in Example 10 in toluene (60 ml), a hexane solution of n-butyllithium (1.54 M, 2.55 ml, 3.93 mmol) was added in an argon atmosphere at −78° C. After stirring for 1 hour at the same temperature, carbon dioxide was bubbled thereinto the mixture. The reaction mixture was allowed to warm to room temperature over 2 hours, subsequently 0.1 N hydrochloric acid was added thereto, and the mixture was extracted with ethyl acetate. The organic layer was dried over anhydrous sodium sulfate and filtered, then the filtrate was concentrated under reduced pressure, and the resulting residue was subjected to flash silica gel chromatography. The fraction obtained from an elution with methylene chloride:methanol=10:1 was concentrated under reduced pressure, and the resulting residue was washed with a mixed solvent of ethanol, diethyl ether and hexane, and was collected by filtration, to obtain the title compound (815 mg, 2.09 mmol, 64%) as a white solid.
