Step A: N-tert-butoxycarbonyl-4-piperidone (5 g, 25 mmol), n-propylamine (3.69 mL, 45 mmol), acetic acid (1.43 mL, 25 mmol), and sodium triacetoxyborohydride (7.95 g, 37.5 mmol) were dissolved in dichloromethane (100 mL) and the reaction was stirred for 16 h at room temperature. After completion of the reaction, the reaction mixture was washed with deionized water (50 mL) and then with saturated sodium bicarbonate solution. The aqueous phase was back-extracted with dichloromethane (20 mL), and all organic phases were combined, dried with anhydrous magnesium sulfate, and concentrated under reduced pressure to give 1-N-Boc-4-propylaminopiperidine 6 g in 95% yield.
