The general procedure for the synthesis of benzyl 3,3-dimethyl-4-oxopiperidine-1-carboxylate from 3,3-dimethylpiperidin-4-one hydrochloride and benzyl chloroformate was as follows: sodium bicarbonate (1.28 g, 15.28 mmol, 2.50 eq.) and benzyl chloroformate (1.25 g, 7.33 mmol, 1.20 eq.) were sequentially added to tetrahydrofuran (5.00 mL) and water (5.00 mL) at 0 °C containing 3,3 -dimethylpiperidin-4-one hydrochloride (1.00 g, 6.11 mmol, 1.00 equiv) in a mixed solution of tetrahydrofuran (5.00 mL) and water (5.00 mL). The reaction mixture was stirred at 15 °C for 12 hours. Upon completion of the reaction, the reaction mixture was extracted with ethyl acetate (20 mL). The organic layers were combined, washed with brine (10 mL x 2), dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford benzyl 3,3-dimethyl-4-oxopiperidine-1-carboxylate (1.60 g, 4.81 mmol, 78.66% yield) as a colorless oil with 78.5% purity. The product was characterized by 1H NMR (400 MHz, CDCl3): δ 7.35-7.25 (m, 6H), 5.11 (s, 2H), 3.72 (t, J = 6.3 Hz, 2H), 3.42 (br.s., 2H), 2.44 (br.s., 2H), 1.02 (br.s., 6H).
