A solution of diethylazodicarboxylate (829 μL) in tetrahydrofuran (10 mL) was added to a cold (−15° C.) stirred solution of N-tert-butoxycarbonyl-trans-4-hydroxy-L-proline (1.23 g), 3-phenylphenol (896 mg), and triphenyl phosphine (1.38 g) in tetrahydrofuran (30 mL) under argon, After stirring at room temperature for 15.5 hr, the solvent was evaporated and coevaporated several times with toluene in vacuo. The residue was diluted with toluene and precipitated solids were removed by filtration, which was washed with toluene. The combined organic layers were evaporated in vacuo and the residue was purified by silica gel column chromatography (ethyl acetate:hexane=1:10, v/v) to give title compound (837 mg): 1H-NMR (400 MHz, CDCl3) δ 1.36-1.50 (m, 9H), 2.18-2.29 (m, 1H), 2.51-2.64 (m, 1H), 3.68-3.89 (m, 5H), 4.40-4.56 (m, 1H), 4.91-5.01 (m, 1H), 6.79-6.87 (m, 1H), 7.04-7.10 (m, 1H), 7.17-7.24 (m, 1H), 7.29-7.39 (m, 2H), 7.39-7.49 (m, 2H), and 7.49-7.60 (m, 2H).
