In benzene (10 ml), 5-tert-butoxycarbonyl-4,5,6,7-tetrahydrothieno[3,2-c]pyridin-2-carboxylic acid (283 mg) was dissolved, followed by the addition of triethylamine (0.14 ml) and diphenylphosphoryl azide (0.21 g). The resulting mixture was heated under reflux for 2 hours. After cooling to room temperature, the reaction mixture was added with 1-[(6-chloronaphthalen-2-yl)sulfonyl]piperazine hydrochloride (347 mg), followed by heating overnight under reflux. After the reaction mixture was cooled to room temperature, dichloromethane and a 3N aqueous sodium hydroxide solution were added thereto to extract an organic layer. The organic layer so extracted was washed with 0.5N hydrochloric acid, a saturated aqueous solution of sodium bicarbonate and saturated saline and dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure. The residue was purified by chromatography on a silica gel column (hexane:ethyl acetate=3:1˜2:1), whereby the title compound (284 mg, 48%) was obtained.
