Wet Degussa-type Pd/C catalyst (10% Pd, 50% water content, 8.120 g, 76.30 mmol) was added to a 3 L three-necked flask under nitrogen protection, followed by EtOAc (1.706 L). The mixture was degassed by a nitrogen/vacuum cycle (3 times). Then, a solution of EtOAc (243.7 mL) of 1-benzyl-4-tert-butylpiperidine-1,4-dicarboxylate (243.7 g, 763.0 mmol) was added. The reaction mixture was stirred overnight under hydrogen atmosphere. After supplementing with hydrogen, stirring was continued for 3.5 hours. Methanol (60 mL) was added to promote dissolution of the precipitate, which was subsequently filtered through a diatomaceous earth pad and washed with methanol. The filtrate was concentrated under reduced pressure to give a brown oil (138.6 g) containing a small amount of white solid. The solid was removed by filtration and washed with a minimal amount of EtOAc. The filtrate was again concentrated under reduced pressure to give tert-butyl piperidine-4-carboxylate (129 g, 91% yield) as a light brown oil. The product was characterized by 1H NMR (500 MHz, DMSO-d6) with chemical shifts of δ 2.88 (dt, 2H), 2.44 (td, 2H), 2.23 (tt, 1H), 1.69-1.64 (m, 2H), 1.41-1.33 (m, 11H).
