Borane-THF complex (1.0 M, 17 mL, 16.9 mmol) was added slowly and dropwise to a stirred solution of (R)-1-(tert-butoxycarbonyl)pyrrolidine-3-carboxylic acid (1.21 g, 5.6 mmol) in tetrahydrofuran (THF, 30 mL) at 0 °C. The reaction mixture was gradually warmed to room temperature over 30 minutes, followed by heating at 45 °C for 1 hour and then at 55 °C for 90 minutes. Upon completion of the reaction, the mixture was cooled to 0 °C and quenched by careful addition of 3N hydrochloric acid (30 mL). After stirring for 20 min at room temperature, the reaction mixture was extracted with ether (Et2O, 50 mL). The organic layer was washed sequentially with saturated aqueous sodium bicarbonate (NaHCO3, 20 mL) and brine (20 mL), dried over anhydrous sodium sulfate (Na2SO4), filtered, and concentrated under reduced pressure to afford (R)-tert-butyl-3-(hydroxymethyl)pyrrolidine-1-carboxylate (1.1 g, 91% yield) as a colorless oil.
