General procedure for the synthesis of methyl 4-piperidinecarboxylate hydrochloride from methyl 1-tert-butoxycarbonyl-4-piperidinecarboxylate: To a dichloromethane (DCM, 3 mL) solution of methyl 1-tert-butoxycarbonyl-4-piperidinecarboxylate (2.16 g, 8.88 mmol) was added a solution of ethyl acetate (EtOAc, 6 mL) of 4 M hydrochloric acid. The reaction mixture was stirred at room temperature for 1.5 h. Subsequent removal of the solvent by concentration under reduced pressure afforded methyl 4-piperidinecarboxylate hydrochloride as a white solid (1.59 g, 99% yield). The product was characterized by 1H NMR (400 MHz, CD3OD): δ 3.73 (s, 3H), 3.44-3.39 (m, 2H), 3.15-3.09 (m, 2H), 2.82-2.77 (m, 1H), 2.21-2.16 (m, 2H), 1.99-1.89 (m, 2H); MS-ESI: m/z 144.2 [M + H - HCl]+.
