To a solution of tert-butyl 4-(hydroxymethyl)piperidine-1-carboxylate (36.1 g, 168 mmol) and NMM (20 mL, 182 mmol) in DCM (500 mL) at 0° C. was added p-nitrophenyl chloroformate (33.9 g, 168 mmol). The reaction mixture was stirred at room temperature overnight and then washed sequentially with 1M aq HCl (500 mL), sat aq NaHCO3 solution (3×500 mL), dried (MgSO4) and concentrated in vacuo to give (1-(tert-butoxy-carbonyl)piperidin-4-yl)methyl 4-nitrophenyl carbonate (61.2 g, 96%) as a yellow solid.
