Water → Butyl 4-hydroxy-2-methylpiperidine-1-carboxylate

To a solution of tert-butyl 2-methyl-4-oxopiperidine-1-carboxylate (0.94 g, 4.41 mmol) in methanol (5 mL) was added sodium borohydride (0.22 g, 5.73 mmol) and the reaction was stirred at room temperature for 1 h. Water was added slowly, followed by ethyl acetate. The layers were separated and the aqueous phase was extracted with ethyl acetate. The combined organic phases were dried over sodium sulfate, filtered and concentrated in vacuo to afford the desired product as a mixture of four stereoisomers, which was used in the next step without further purification.