To a solution of (3R,4R)-di-tert-butyl 4-aminopyrrolidine-1,3-dicarboxylate (Org. Biomol. Chem. 2004, 2, 2763-2776) (430 mg, 1.5 mmol) in dichloromethane/methanol (18 mL/2 mL) was added benzaldehyde (153 uL, 1.5 mmol) and sodium triacetoxyborohydride (1.89 g, 9.0 mmol). The mixture was stirred overnight and partitioned between ethyl acetate and water. The organic layer was washed with brine, dried with magnesium sulfate, filtered and evaporated. The residue was purified on silica gel eluting with ethyl acetate/hexane (1:3) to give the title compound (495 mg, 88%). MS (ESI+) m/z=377 (M+H)+.
