Tributyltin hydride (91 μL) and azobisisobutyronitrile (8.5 mg) were added to a solution of O-[1-(6-{(E)-1-(4-tert-butylphenyl)-2-[(2R)-1-(2,4-dimethoxybenzyl)-5-oxopyrrolidin-2-yl]ethenyl}-2-methoxypyridin-3-yl)ethyl] S-methyl carbonodithioate (109 mg) in toluene (2 mL), and the mixture was stirred at 120° C. for 30 minutes. Water was added to the reaction solution, followed by extraction with chloroform. The organic layer was dried over anhydrous magnesium sulfate and filtered. The solvent was then evaporated under reduced pressure. The residue was purified by silica gel column chromatography (hexane:ethyl acetate=3:1) to give (5R)-5-[(E)-2-(4-tert-butylphenyl)-2-(5-ethyl-6-methoxypyridin-2-yl)ethenyl]-1-(2,4-dimethoxybenzyl)pyrrolidin-2-one as a colorless oil (65 mg).
