Hydrochloric Acid → (2S,4S)-1-(Tert-butoxycarbonyl)-4-(2,4-difluoro-phenoxy)-2-pyrrolidinecarboxylic acid

To a stirred solution of methyl 1-(tert-butoxycarbonyl)-4-(2,4 difluorophenoxy)pyrrolidine-2-carboxylate (5.82 g, 16.3 mmol) in THF (130 ml) was added 0.25 N NaOH (130 ml, 32.6 mmol). The resulting mixture was stirred overnight. The mixture was poured into 1 N HCl (100 ml) and extracted with CHCl3 (2×200 ml). The extracts were dried over MgSO4 and evaporated. The residue was chromatographed on silica gel with CHCl3-EtOAc (4:1) as eluent to give 1-(tert-butoxycarbonyl)-4-(2,4-difluorophenoxy)pyrrolidine-2-carboxylic acid (2.55 g, 46%) as a colorless foam. 1H-NMR (CDCl3) δ 1.42–1.47 (m, 9 H), 2.29–2.74 (series of m, 2 H), 3.66–3.71 (m, 2 H), 4.46–4.51 (m, 1 H), 4.83 (m, 1 H), 6.73–6.95 (m, 3 H).