To a solution of (R)-tert-butyl 3-((R)-(2-aminoethoxy)(2,3-difluorophenyl)methyl)piperidine-1-carboxylate (195 mg, 0.402 mmol), DMAP (25.8 mg, 0.201 mmol) and Et3N (0.18 mL) in dry CH2Cl2 at 0° C. was added methyl chloroformate (189 mg, 2.013 mmol), the mixture was allowed to warm to rt and stirred overnight. The mixture was concentrated in vacuo to give the crude product (R)-tert-butyl 3-((R)-(2,3-difluorophenyl)(2-(methoxycarbonylamino)ethoxy)methyl)piperidine-1-carboxylate (168 mg, 98%), which was used in the next step without further purification. 1H NMR (CDCl3, 400 MHz) δ 7.21 (m, 3H), 4.57 (m, 1H), 4.44 (d, 1H), 4.08 (m, 1H), 3.82 (m, 1H), 3.53 (s, 3H), 3.29 (d, 2H), 2.93 (m, 2H), 1.79 (m, 1H), 1.63 (m, 1H), 1.43 (s, 9H), 1.34 (m, 3H).
