Step 1. To a stirred solution of tert-butyl 3-hydroxypiperidine-1-carboxylate (5 g, 24.84 mmol) and triethylamine (5.027 g, 6.924 mL, 49.68 mmol) in dichloromethane (50 mL) was slowly added methanesulfonyl chloride (3.130 g, 2.115 mL, 27.32 mmol) under the conditions of an ice bath at 0°C. The reaction mixture was gradually warmed to room temperature over 3 hours. Upon completion of the reaction, the reaction mixture was washed with water and 1 M hydrochloric acid, followed by drying with magnesium sulfate, filtration and concentration in vacuum to afford tert-butyl 3-((methanesulfonyl)oxy)piperidine-1-carboxylate as a yellow oil (7.9 g, quantitative yield, with a small amount of residual solvent).1H NMR (400.0 MHz, CDCl3) δ 1.49 (s, 9H), 1.60- 1.57 (m, 1H), 2.04-1.79 (m, 3H), 3.08 (s, 3H), 3.38-3.32 (m, 1H), 3.50-3.43 (m, 1H), 3.70-3.60 (m, 2H) and 4.74 (br s, 1H) ppm.
