Into 10 mL of THF was dissolved 135 mg of methyl 4-amino-5-methanesulfonyl-2-methylbenzoate, followed by addition of 22 mg of sodium hydride (oily, 60%) at room temperature. After 20 minutes of stirring at the same temperature, 130 mg of 5-chloro-2-chlorosulfonyl-3-methylbenzo[b]thiophene was added at 0° C., followed by 1 hour of stirring at room temperature and 5 hours of heating under refluxing. Further, 1 mL of DMF, 22 mg of sodium hydride (oily, 60%) and 50 mg of 5-chloro-2-chlorosulfonyl-3-methylbenzo[b]thiophene were added and the mixture was heated under refluxing for 2.5 hours. After confirmation of disappearance of the starting material, the reaction was terminated by adding saturated aqueous ammonium chloride solution at 0° C., followed by extraction with ethyl acetate. The organic layer was washed with saturated brine and then dried over anhydrous sodium sulfate. The solvent was removed by evaporation and the residue was purified by silica gel column chromatography (ethyl acetate/hexane=3/2) to obtain 102 mg of the title compound as colorless powder.
