The general procedure for the synthesis of methyl S-pyrrolidine-3-carboxylate hydrochloride from methanol and (S)-1-BOC-pyrrolidine-3-carboxylic acid was as follows: to a stirred solution of (3S)-1-{[(1,1-dimethylethyl)oxy]carbonyl}-3-pyrrolidinecarboxylic acid (1.0 g, 4.6 mmol) in methanol (25 mL) was slowly added dropwise, protected by nitrogen and at room temperature, to a stirred solution of Thionyl chloride (1.63 g, 13.7 mmol). The reaction mixture was heated to reflux for 2 hours and subsequently cooled to room temperature. The reaction mixture was concentrated to give 0.766 g (100% yield) of methyl(3S)-3-pyrrolidinecarboxylic acid hydrochloride, initially as an oil, which solidified on standing. The product was characterized by 1H NMR (400 MHz, CDCl3): δ 9.91 (m, 2H), 3.76 (s, 3H), 3.59 (br s, 2H), 3.49 (br s, 2H), 3.28 (br s, 1H), 2.33 (br s, 2H).
