Benzyl chloroformate (95%, 4.52 mL, 30.1 mmol) was added dropwise to a stirred mixture of tert-butyl 4-(3-amino-6-methylphenyl)piperidinecarboxylate (6.99 g, 24.1 mmol) and K2CO3 (3.66 g, 26.4 mmol) in tetrahydrofuran (350 mL) and stirred under nitrogen for 18 h. CH2Cl2 was added to the reaction mixture, washed with NaHCO3 solution (saturated), followed by water, then dried over Na2SO4 and concentrated in vacuo to give an oil. Purification by flash column chromatography (eluent: cyclohexane:EtOAc (87:13)) gave tert-butyl 4-{2-methyl-5-[(phenylmethoxy)carbonylamino]phenyl}piperidinecarboxylate (7.90 g, 77.1% yield) as a white foam. ESMS m/e: 425.0 (M+H)+.
