To a solution of {(3aR,6aS)-2-[2,4-bis(trifluoromethyl)benzyl]octahydrocyclopenta[c]pyrrol-5-yl}methanol (1.4 g) and triethylamine (3.19 mL) in DMSO (7 mL) and ethyl acetate (7 mL) was added sulfur trioxide pyridine complex (1.82 g) under cooling to 0° C. The reaction mixture was stirred at room temperature for 1 hr. Water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The extract was washed with water and saturated brine, and dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/hexane) to give the title compound (900 mg).
