Sodium Hydroxide → (S)-3-Boc-2,2-dimethyloxazolidine-4-propanoic Acid

Sodium hydroxide (27 mL of a 4.0 M solution in H2O, 108 mmol, 3.0 equiv.) was added to a solution of (4S)-4-(2-methoxycarbonylethyl)-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester (prepared as described in Chida et al., J. Chem. Soc., Chem. Commun. 1992, 1064) (10.5 g, 36.5 mmol, 1 equiv.) in CH3OH (150 mL), and the resulting cloudy reaction mixture was stirred at 23° C. for 3.5 h. The mixture was concentrated under reduced pressure to 30 mL volume, and then was partitioned between 0.5 M HCl (150 mL) and EtOAc (2×150 mL). The combined organic layers were dried over MgSO4 and were gravity filtered. The filtrate was concentrated under reduced pressure and the residue dried under vacuum, to afford (4S)-4-(2′-carboxyethyl)-2,2-dimethyloxazolidine-3-carboxylic acid tert-butyl ester (10.0 g, 100% crude yield). This material was used without further purification: 1H NMR (CDCl3, mixture of rotamers) δ 1.49 (s), 1.57 (s), 1.60 (s), 1.84–2.05 (m), 2.39–2.41 (m), 3.71–3.74 (m), 3.91–4.05 (m).