General procedure for the synthesis of methyl N-Boc-4-piperidineacetate from tert-butyl 4-(2-methoxy-2-oxoethylidene)piperidine-1-carboxylate: 1-tert-butoxycarbonyl-4-[(methoxycarbonyl)methylidene]piperidine (875 mg) was dissolved in ethanol (10 mL), to which 10% of palladium-carbon catalyst (~50% water content, 730 mg) was added. The reaction mixture was subjected to catalytic hydrogenation at room temperature and at atmospheric pressure for 3 days. Upon completion of the reaction, the catalyst was removed by filtration and the solvent was subsequently removed by distillation under reduced pressure to afford the target product methyl N-Boc-4-piperidineacetate (871 mg, 99% yield). The product was characterized by 1H-NMR (CDCl3): δ 1.16 (2H, m), 1.45 (9H, s), 1.65 (2H, m), 1.93 (1H, m), 2.25 (2H, d, J = 6.8 Hz), 2.72 (2H, br), 3.68 (3H, s), 4.08 (2H, br). Mass spectrometry (FAB) analysis showed m/z: 258 (M + H)+.
