To a stirred solution of methyl 4-piperidinecarboxylate (7.00 mmol) in methanol (25 mL) was sequentially added formic acid (5.52 g, 12.00 mmol) and 40% aqueous formaldehyde (2.67 g, 35.00 mmol). The reaction mixture was heated to reflux. after 3 h, the reaction mixture was cooled and concentrated under reduced pressure. The residue was dissolved in water, alkalized with sodium bicarbonate solution and extracted with dichloromethane (3 x 30 mL). The organic layers were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give methyl N-methyl-4-piperidinecarboxylate in brown liquid form (yield: 910 mg). NMR hydrogen spectrum (270 MHz, CDCl3, TMS as internal standard) δ: 1.69-2.03 (6H, m), 2.23-2.32 (4H, m), 2.78-2.83 (2H, m), 3.68 (3H, s). Mass spectrum (APCI) m/z: 158 ([M+H]+, 100%), 126 (C7H12ON, 33%).
