Tert-butyl 4-(3-aminophenyl)-5,6-dihydropyridine-1(2H)-carboxylate (3.10 g, 11.3 mmol) was used as a raw material and mixed with 10% Pd/C (1.00 g) in ethanol (100 mL). The reaction system was hydrogenated at room temperature for 2 days using the balloon method. After completion of the reaction, the mixture was filtered through diatomaceous earth and the filter cake was washed with ethanol. The ethanol extracts were combined and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with the eluent dichloromethane:methanol:isopropylamine (95:5:1, v/v/v) to afford the target product tert-butyl 4-(3-aminophenyl)-piperidine-1-carboxylate (2.63 g, 84% yield). The product was characterized by 1H NMR (400 MHz, CDCl3): δ 7.10 (t, 1H, J = 7.6 Hz), 6.62 (d, 1H, J = 8.4 Hz), 6.60-6.59 (m, 2H), 4.27-4.18 (m, 2H), 3.62-3.58 (m, 2H), 2.80-2.72 (m, 2H), and 2.62-2.59 (m, 1H), 1.89-1.52 (m, 4H), 1.49 (s, 9H); ESMS m/e: 277.2 (M + H)+.
