N-Boc-D-valine (85 mg, 0.39 mmol), EDC (75 mg, 0.39 mmol), HOBt (53 mg, 0.39 mmol) was dissolved in dichloromethane (2 mL). 4-(4-Chloro-3-methoxyphenyl)-3,3-dimethylpiperidin-4-ol hydrochloride (100 mg, 0.33 mmol) was added followed by DIPEA (136 μL, 0.78 mmol) and the solution was stirred at rt for 10 min. The reaction was concentrated and the resulting oily residue was purified via column chromatography (10% to 50% EtOAc/heptane) to furnish tert-butyl (2R)-1-(4-(4-chloro-3-methoxyphenyl)-4-hydroxy-3,3-dimethylpiperidin-1-yl)-3-methyl-1-oxobutan-2-ylcarbamate (153 mg, 99% yield) MS found: (M-Boc)+=396.3.
