[NH2:1][C@@H:2]1[CH2:6][CH2:5][N:4]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[CH2:3]1.C(O[C:17]1(O[Si](C)(C)C)[CH2:19][CH2:18]1)C.C([BH3-])#N.[Na+].C(O)(=O)C>CO>[CH:17]1([NH:1][C@@H:2]2[CH2:6][CH2:5][N:4]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[CH2:3]2)[CH2:19][CH2:18]1To a solution of (R)-tert-butyl 3-aminopyrrolidine-1-carboxylate (400 mg, 2.15 mmol), (1-ethoxycyclopropoxy)trimethylsilane (1500 mg, 8.60 mmol) in methanol (30 mL) was added sodium cyanoborohydride (569 mg, 8.60 mmol) and acetic acid (0.2 mL). The mixture was stirred at reflux for 10 h. The volatiles were removed under reduced pressure. The residue was treated with water (20 mL) and extracted with ethyl acetate (3×30 mL). The combined extracts were washed with brine (3×10 mL), dried over anhydrous Na2SO4, filtered, and concentrated to give the title compound. MS (m/z): 227 (M+H)+.
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