To a solution of 1-tert-butoxycarbonyl-4-(2-hydroxyethyl)piperazine (7.40 g, 32.13 mmol) in THF (100 mL), triethylamine (4.36 g, 43.09 mmol), 4-dimethylaminopyridine (200 mg, 1.64 mmol) and methanesulfonyl chloride (7.40 g, 38.76 mmol) were successively added under ice cooling and stirring. The temperature of the reaction mixture was allowed to rise to room temperature, at which the reaction mixture was stirred for 50 minutes. The reaction mixture was filtered, and the filtrate was concentrated under reduced pressure. The residue was dissolved in DMF (200 mL). At room temperature, 5,6-difluoro-2-mercaptobenzimidazole (5.00 g, 26.86 mmol), potassium carbonate (8.64 g, 62.51 mmol) and 18-crown-6 (500 mg, 1.92 mmol) were successively added, followed by stirring at 80° C. for 90 minutes. The reaction mixture was concentrated under reduced pressure, and the residue was purified by column chromatography on silica gel (silica gel: 200 g; developer: hexane:acetone=8:1→1:1). Crystallization was conducted from acetone-ethyl ether-hexane to obtain the title compound (7.26 g, yield: 680) as colorless crystals.
