Methyltriphenylphosphonium bromide (187.4 mg, 0.52 mmol) was dissolved in tetrahydrofuran. A 2.62 M solution of n-butyllithium in hexane (0.16 mL, 0.42 mmol) was added dropwise in a nitrogen atmosphere at −78° C., and the mixture was stirred for one hour. After heating to 0° C., a solution of (3S)-3-formyl-5-oxo-1-[(1R)-1-phenylethyl]pyrrolidine-3-carboxylic acid tert-butyl ester (111 mg, 0.35 mmol) in tetrahydrofuran was added dropwise, and the mixture was stirred for one hour. A saturated ammonium chloride solution was added to the reaction solution, followed by extraction with ethyl acetate. The organic layer was washed with water and brine, dried over anhydrous sodium sulfate, and filtered. The solvent was evaporated under reduced pressure, and the resulting residue was subjected to silica gel column chromatography (25% ethyl acetate/hexane) to give 54 mg of the title compound as a yellow oil.
