General procedure for the synthesis of ethyl 4-piperidineacetate from ethyl 2-(1-benzylpiperidin-4-ylidene)acetate: palladium/carbon catalyst (3.94 g) was added to a solution of 2-(1-benzylpiperidin-4-ylidene)ethyl acetate (24 g, 93 mmol) in ethyl acetate (300 mL). The reaction mixture was placed in an H-cubic hydrogenation reactor and the reaction conditions were set at 55 °C and 55 psi for 16 hours. Upon completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated under reduced pressure to afford ethyl 4-piperidineacetate as a colorless oil (15 g, 90% yield). The product was characterized by 1H NMR (400 MHz, CDCl3) with chemical shifts δ: 4.10 (m, 2H), 3.03 (d, J = 16.4 Hz, 2H), 2.59 (t, J = 16.4 Hz, 2H), 2.19 (d, J = 9.6 Hz, 2H), 1.87 (m, 1H), 1.67 (d, J = 17.2 Hz, 2H ), 1.23 (t, J = 9.6Hz, 3H), 1.10 (m, 2H).
