N-Boc-4-hydroxypiperidine (10 g, 49.68 mmol, 1 eq.) and triethylamine (7.54 g, 74.50 mmol, 1.5 eq., 10.38 ml) were dissolved in anhydrous dichloromethane (200 ml) and cooled to 0-5 °C. Methylsulfonyl chloride (6.88 g, 60.12 mmol, 4.65 ml, 1.21 eq.) was added slowly and dropwise under stirring. The reaction mixture was stirred at 0-5 °C for 3 hours. After completion of the reaction, the mixture was diluted with dichloromethane (200 ml), transferred to a separatory funnel and washed sequentially with 2M aqueous sodium carbonate solution (200 ml) and saturated sodium chloride solution (200 ml). The organic layer was dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give 14.51 g of tert-butyl 4-((methylsulfonyl)oxy)piperidine-1-carboxylate as a white solid (yield = 100%). The product was confirmed by 1H-NMR (400 MHz, DMSO-d6) and mass spectrometry (EI): δ 4.80 (m, 1H), 3.39 (m, 2H), 3.29 (m, 2H), 2.94 (s, 3H), 1.77 (m, 2H), 1.52 (m, 2H); MS (EI): 280 (MH+).
