To a solution of N-tert-butoxycarbonyl-4-piperidone (1 g, 5.0 mmol) in methanol (20 mL) was sequentially added acetic acid (0.3 mL, 5.0 mmol), 2-methoxyethylamine (0.44 mL, 5.0 mmol), and sodium cyanoborohydride (346 mg, 5.5 mmol). The reaction mixture was stirred at 25°C for 12 hours. After completion of the reaction, the reaction solution was diluted with aqueous sodium carbonate and extracted with ethyl acetate several times. The organic phases were combined, concentrated and purified by silica gel column chromatography (eluent: dichloromethane/methanol, 0-10% gradient) to afford tert-butyl 4-(2-methoxyethylamino)piperidine-1-carboxylate (1.2 g, 93%) as a yellow oil.LC/MS (ES) m/e 259 (M+H)+.
