To a solution of LDA (prepared by adding n-BuLi (27.7 mL, 55.5 mmol) to diisopropylamine (8.04 mL, 57.3 mmol) in THF (40 mL) at 0° C., stir for 30 min) was added 1-tert-butyl 4-methyl piperidine-1,4-dicarboxylate (4500 mg, 18.5 mmol) in TMEDA (16.6 mL, 111 mmol) dropwise via syringe pump at −78° C. for 20 min. The mixture was stirred at the same temperature for 30 min, and (S)-tert-butyl (1-oxopropan-2-yl)carbamate (9931 mg, 57.3 mmol) in THF (20 mL) was added slowly by syringe pump for 20 min. The mixture was stirred at −78° C. for 30 min, and quenched with saturated NH4Cl at −78° C., warmed up to rt and diluted with EtOAc (200 mL). The organic layer was separated, and the aqueous layer was extracted with EtOAc (100 mL). The combined organic layers were washed with brine, dried (MgSO4), and concentrated. The residue was purified by column chromatography (MeOH/DCM, gradient 0-10%) to afford the title compound. LC/MS: [(M+1)]+=417
