Synthesis of tert-butyl 2,6-dimethyl-4-oxopiperidine-1-carboxylate (9.37): 2,6-dimethylpiperidin-4-one (9.36, 3.6 g, 28.34 mmol) was dissolved in dichloromethane (DCM, 50 mL) at 0°C. Triethylamine (Et3N, 9.8 mL, 70.8 mmol) and di-tert-butyl dicarbonate ( Boc2O, 12.1 mL, 56.6 mmol). The reaction mixture was stirred at room temperature for 16 hours. The reaction process was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture was diluted with water and extracted (3 times) with DCM. The organic phases were combined, washed with saturated saline, dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated. The crude product was purified by silica gel column chromatography (100-200 mesh, 10-15% ethyl acetate-hexane) to afford the target compound 9.37 (3.9 g, 60.9% yield).1H NMR (400 MHz, CDCl3): δ 2.85 (d, J = 6.4 Hz, 1H), 2.81 (d, J = 6.4 Hz, 1H), 2.38- 2.39 (m, 2H), 2.34-2.36 (m, 2H), 1.48 (s, 9H), 1.25-1.27 (m, 6H). MS: 228.08 (M + H)+.
