A solution 4-(benzyloxycarbonylamino)-1-(tert-butoxycarbonyl)piperidine-4-carboxylic acid (1A, 2.0 g, 1.0 equivalent) in DME (0.5 M) was treated with NMM (1.0 equivalent) and IBCF (1.0 equivalent) at −15° C. After 10 min, aqueous ammonia (1.5 equivalents) was added. The reaction mixture was stirred at room temperature for 1.5 hr. The reaction was complete as determined by LCMS analysis and then partitioned between ethyl acetate and water. The organics were subsequently washed with brine, then dried over Na2SO4, filter, and the volatiles removed under reduced pressure. The residue was purified by crystallization from diethyl ether to afford the tert-butyl 4-(benzyloxycarbonylamino)-4-carbamoylpiperidine-1-carboxylate (1B, 70%).
