To a stirred solution of (3R)-1-{[(1,1-dimethylethyl)oxy]carbonyl}-3-pyrrolidinecarboxylic acid (1.03 g, 4.8 mmol) in methanol (25 mL) was added thionyl chloride (1 mL, 13.7 mmol) dropwise at room temperature under the protection of nitrogen atmosphere. The reaction mixture was heated to reflux for 2 hours and then cooled to room temperature. The reaction mixture was concentrated and the crude product was dissolved in dichloromethane. The solution was further concentrated to give 0.792 g (100% yield) of methyl (3R)-3-pyrrolidine carboxylic acid hydrochloride as an off-white solid. The product was characterized by 1H NMR (400 MHz, CDCl3): δ 9.93 (m, 2H), 3.74 (s, 3H), 3.58 (br s, 2H), 3.42 (br s, 2H), 3.26 (m, 1H), 2.36-2.25 (m, 2H).
