To a solution of 1-(tert-butyl) 2-methyl (S)-4,4-dimethylpyrrolidine-1,2-dicarboxylate (4.85 g, 18.86 mmol) in THF (40 mL) was dropwise added lithium hydroxide monohydrate aqueous solution (1.5 g, 20 mL) at 0 °C. At the end of the addition, the mixture was stirred at rt for 2.0 h. After that, the THF solvent was removed and 50 mL of water was added to the mixture. The resulting mixture was washed with EtOAc (30 mL x 3). The aqueous phase was adjusted to pH=1 with hydrochloric acid (1 M) and extracted with EtOAc (50 mL x 3). The combined organic layers were washed with brine, dried over anhydrous Na2S04, and concentrated in vacuo to give (S)-1-(tert-Butoxycarbonyl)-4,4-dimethylpyrrolidine-2-carboxylic acid as a white solid (4.35 g, 95%).
