18.9 g (86.2 mmol) of benzyl 4-hydroxypiperidine-1-carboxylate, 25.4 g (86.2 mmol) of methyl (2S)-2-(t-butoxycarbonylamino)-3-(4-hydroxyphenyl)propionate and 27.1 g (103.4 mmol) of triphenylphosphine were dissolved in 500 ml of tetrahydrofuran. 37.5 g (86.2 mmol) of diethyl azodicarboxylate was added to the solution at room temperature, and they were stirred for 15 hours. After the isolation treatment with ethyl acetate as the extractant in the same manner as that of step 1 in Example 1, the crude product was obtained, which was purified by the silica gel column chromatography to obtain the title compound.
