Sodium triacetoxyborohydride (11.2 g, 52.6 mmol) was added to a solution of methyl 2-aminopent-4-enoate (3.4 g, 26.3 mmol), acetic acid (2.37 g, 39.5 mmol) and benzyl 4-oxopiperidine-1-carboxylate (9.21 g, 39.5 mmol) in dichloroethane (60 mL) at room temperature. After 3 h, the reaction was quenched with saturated aqueous sodium bicarbonate, extracted with methylene chloride (3×), dried over sodium sulfate, filtered and evaporated to give the crude product. This was purified by chromatography (silica gel, 0 to 8% methanol in methylene chloride gradient elution), which gave the title compound (9.42 g). MS 347.2 (M+1).
