Pyridine → Methyl 3-(cyclopropyl(methyl)amino)-2-(trifluoromethylsulfonyloxy)quinoxaline-6-carboxylate

To a solution of methyl 3-(cyclopropyl(methyl)amino)-2-oxo-1,2-dihydroquinoxaline-6-carboxylate (240 mg, 0.88 mmol) in DCM (50 mL) was added pyridine (280 mg, 3.54 mmol) and Tf2O (496 mg, 1.76 mmol). The resulting solution was stirred 3 h at room temperature and then dissolved in water/ice (100 mL), extracted with dichloromethane (3×20 mL), dried over anhydrous magnesium sulfate and concentrated under vacuum to afford methyl 3-(cyclopropyl(methyl)amino)-2-(trifluoromethylsulfonyloxy)quinoxaline-6-carboxylate as a red oil (300 mg, crude), which was used to the next step directly.