An excessive amount of a solution of diazomethane in diethyl ether (30 mL) was added to (3S,4S)-1-benzyloxycarbonyl-3-(tert-butoxycarbonyl)amino-4-vinylpyrrolidine (270 mg, 779 mmol). Under cooling with ice, palladium acetate (10 mg) was added thereto, followed by stirring at room temperature for 2 hours. After completion of reaction, insoluble matter was removed through filtration. The filtrate was concentrated under reduced pressure, and the obtained residue was purified though silica gel column chromatography (ethyl acetate:n-hexane=1:9 to 1:4), to thereby yield the title compound as a colorless oily substance (269 mg, 96%).
