[N:1]([C@H:4]1[C@H:8]([O:9][CH3:10])[CH2:7][N:6]([C:11]([O:13][C:14]([CH3:17])([CH3:16])[CH3:15])=[O:12])[CH2:5]1)=[N+]=[N-].[H][H].C>CO.O=[Pt]=O>[NH2:1][C@H:4]1[C@H:8]([O:9][CH3:10])[CH2:7][N:6]([C:11]([O:13][C:14]([CH3:17])([CH3:16])[CH3:15])=[O:12])[CH2:5]1
A mixture of (3R,4R)-tert-butyl 3-azido-4-methoxypyrrolidine-1-carboxylate (2.04 g, 8.420 mmol) and PtO2 (0.096 g, 0.42 mmol) in MeOH (100 mL) was charged with hydrogen (1 atmosphere) and stirred at ambient temperature for 2 days. Charcoal (2 g) was added to the solution and. The catalyst was removed by filtration and washed with MeOH (20 mL). The solvent was removed and dried to give (3R,4R)-tert-butyl 3-amino-4-methoxypyrrolidine-1-carboxylate. It was dissolved in dioxane (10 mL) and water (10 mL). Na2CO3 (1.34 g, 12.63 mmol) was added, followed by Cbz-Cl (1.87 mL, 12.63 mmol) at ambient temperature. The reaction mixture was stirred at ambient temperature for 3 hours. Ethyl acetate (50 ml) was added. The organic layer was separated, washed with brine, dried (sodium sulfate), filtered and concentrated under reduced pressure. The residue obtained was purified by flash chromatography on silica gel (1:1 hexane/ethyl acetate) to give (3R,4R)-tert-butyl 3-(benzyloxycarbonylamino)-4-methoxypyrrolidine-1-carboxylate (2.90 g, 98.3% yield) as oil.
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