Pyridine → (S)-methyl 3-(2-methylpyrrolidin-1-yl)-2-(trifluoromethylsulfonyloxy)quinoxaline-6-carboxylate

To a solution of methyl 3-((S)-2-methylpyrrolidin-1-yl)-2-oxo-1,2,4a,8a-tetrahydroquinoxaline-6-carboxylate (140.0 mg, 0.48 mmol) in dichloromethane (50 mL) was added pyridine (152 mg, 1.92 mmol) and Tf2O (271 mg, 0.96 mmol), and the reaction mixture was stirred overnight under an atmosphere of nitrogen at room temperature. The reaction mixture was then quenched with water (50 mL), extracted with dichloromethane (3×15 mL), and the organic layers combined, dried over anhydrous magnesium sulfate, and concentrated in vacuo to afford (S)-methyl 3-(2-methylpyrrolidin-1-yl)-2-(trifluoromethylsulfonyloxy)quinoxaline-6-carboxylate as red oil (195 mg, crude), which was used in the next step directly.