The general procedure for the synthesis of tert-butyl 4-hydroxy-3-methylpiperidine-1-carboxylate from N-Boc-3-methyl-piperidin-4-one was as follows:
(i) Sodium borohydride (0.265 g, 7.03 mmol) was added batchwise to a solution of (R,S)-tert-butyl-3-methyl-4-oxopiperidine-1-carboxylate (1.0 g, 4.68 mmol) in methanol (10 mL) at 0 °C. The reaction mixture was kept stirred at 0 °C for 1 hour, then warmed up to room temperature and continued stirring for 2.5 hours. Upon completion of the reaction, the reaction was quenched with saturated aqueous ammonium chloride solution and concentrated under reduced pressure to remove methanol. The reaction mixture was extracted with dichloromethane, the organic layers were combined and dried over anhydrous sodium sulfate. After filtration, the organic layer was concentrated under reduced pressure to afford the target product tert-butyl 4-hydroxy-3-methylpiperidine-1-carboxylate as a colorless oil (quantitative yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3) and mass spectrometry (ES+): 1H NMR δppm 0.87-0.94 (m, 3H), 1.33-1.88 (m, 3H), 1.38 (s, 9H), 2.23-4.08 (m, 5H); MS: ES+ 216.
