[CH3:1][C:2]1([CH3:21])[CH2:6][N:5](C(OC(C)(C)C)=O)[CH:4]([C:14]([O:16]C(C)(C)C)=[O:15])[CH2:3]1.[C:22]([OH:28])([C:24]([F:27])([F:26])[F:25])=[O:23]>C(Cl)Cl>[CH3:1][C:2]1([CH3:21])[CH2:6][NH:5][CH:4]([C:14]([OH:16])=[O:15])[CH2:3]1.[C:22]([OH:28])([C:24]([F:27])([F:26])[F:25])=[O:23]A mixture of 137e (27 g, 90 mmol) and TFA (100 mL) in DCM (200 mL) was stirred at 20° C. for 16 h. See FIG. 1. The reaction solution was concentrated under reduced pressure to give 4,4-dimethylpyrrolidine-2-carboxylic acid 137f as a brown oil (27 g, TFA salt). 1H NMR (400 MHz, CDCl3): δ 12.08 (br s, 2H), 9.56 (br s, 1H), 7.77 (br s, 1H), 4.52 (s, 1H), 3.20 (s, 2H), 2.30-2.24 (m, 1H), 2.00-1.94 (m, 1H), 1.17 (s, 6H).
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