Step 3: 1-tert-butyl 3-methyl 3-fluoropyrrolidine-1,3-dicarboxylate (414.4 mg, 1.676 mmol) was dissolved in a 3:1 THF/MeOH solvent mixture (5.6 mL), and 2.0 M KOH aqueous solution (2.1 mL, 4.19 mmol) was added. The reaction mixture was stirred at room temperature for 2 hours. Upon completion of the reaction, the organic solvent was removed by distillation under reduced pressure. The residue was diluted with 20% isopropanol/dichloromethane (IPA/DCM) mixed solvent and subsequently acidified to pH 3 with 1.0 M aqueous HCl. The resulting mixture was extracted twice with 20% IPA/DCM mixed solvent, the organic phases were combined, washed twice with water, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to afford 1-(tert-butoxycarbonyl)-3-fluoropyrrolidine-3-carboxylic acid ( 352.8 mg, 90.3% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ= 13.80 (s, 1H), 3.69-3.54 (m, 3H), 3.36-3.32 (m, 1H), 2.43-2.24 (m, 2H), 1.40 (s, 9H).
