Triethylamine → (R)-(5-oxopyrrolidin-2-yl)methyl methanesulfonate

To a solution of commercially available (R)-(−)-5-(hydroxymethyl)pyrrolidin-2-one (5 g, 43.4 mmol) in ethanol-free CHCl3 (150 ml), Et3N (6.9 g, 68.3 mmol) and methanesulfonyl chloride (5.96 g, 52.0 mmol) were added dropwise at 0° C. The mixture was left stirring at room temperature for 3 hours, then it was diluted with DCM and washed with a saturated aqueous solution of NaHCO3. After drying (Na2SO4) the solvent was removed under reduced pressure and the residue was purified by flash chromatography (DCM/MeOH 95/5 respectively) to give the title compound as a pale yellow solid (5.9 g, 70% yield).