Under a nitrogen stream, sodium hydride (60% in mineral-oil dispersion) (44 mg, 1.1 mmol) was suspended in tetrahydrofuran (5 mL), followed by addition of ethyl diethylphosphonoacetate (0.24 mL, 1.2 mmol), and the mixture was stirred for 10 minutes at room temperature. A tetrahydrofuran solution of [(1S,3R)-3-(4-formylphenyl)cyclopentyl][(1R)-1-(naphthalen-1-yl)ethyl]carbamic acid tert-butyl ester (407 mg, 0.92 mmol) was added to the mixture, and the mixture was stirred further for 1 hour at room temperature. A saturated aqueous ammonium chloride solution was added to the reaction solution, and the solution was extracted with ethyl acetate. The extracted solution was dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. The residue obtained was purified by column chromatography (ethyl acetate/hexane: 10/90-15/85) to give the title compound (475 mg).
