General procedure for the synthesis of (S)-5-bromomethyl-2-pyrrolidinone from (S)-(+)-5-hydroxymethyl-2-pyrrolidinone: First, (S)-5-hydroxymethyl-2-pyrrolidinone (1.58 g, 13.7 mmol) and triphenylphosphine (3.97 g, 15.1 mmol) were suspended in anhydrous acetonitrile (20 mL) and stirred at 0 °C. Subsequently, a solution of carbon tetrabromide (5.02 g, 15.1 mmol, 1.1 eq.) dissolved in 8 mL of anhydrous acetonitrile was added slowly and dropwise. The reaction mixture gradually changed to a clarified solution, followed by stirring at room temperature overnight. Upon completion of the reaction, the solvent was removed by rotary evaporation and the residue was purified by Biotage fast chromatography to afford the target product (S)-5-bromomethyl-2-pyrrolidinone as a white solid (2.32 g, 95% yield). The structure of the product was confirmed by 1H NMR (400 MHz, CD3OD): δ 6.18 (br s, 1H), 3.94-3.97 (m, 1H), 3.28-3.44 (m, 2H), 2.27-2.49 (m, 3H), 1.82-1.91 (m, 1H).
