To a solution of (R)-tert-butyl 3-((R)-(2-aminoethoxy)(3-chlorophenyl)methyl)piperidine-1-carboxylate (1.05 g, ca. 2.6 mmol), Et3N (3.96 mL, 2.85 mmol), and DMAP (174 mg, 1.43 mmol) in anhydrous CH2Cl2 (20 mL) cooled to 0° C. was added a solution of methyl chloroformate (1.35 g, 14.25 mmol) in dichloromethane (20 mL) within 30 min. The reaction was stirred overnight, and evaporated under vacuum. The residue was purified by flash chromatography on silica gel to afford (R)-tert-butyl 3-((R)-(3-chlorophenyl)(2-(methoxycarbonylamino)ethoxy)methyl)piperidine-1-carboxylate (0.65 g). MS: 427 (M+H)+.
