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

To a solution of (S)-methyl 3-(2-methylpiperidin-1-yl)-2-oxo-1,2-dihydroquinoxaline-6-carboxylate (840 mg, 2.79 mmol) in dichloromethane (60 ml) was added pyridine (1.19 g, 14.98 mmol) and then Tf2O (2.12 g, 7.52 mmol) dropwise with stirring at 0° C. The resulting solution was stirred overnight at room temperature, then washed with water (3×50 ml), dried over anhydrous sodium sulfate and concentrated under vacuum to give a residue, which was purified via silica gel chromatography (1% to 2% ethyl acetate in petroleum ether) to afford (S)-methyl 3-(2-methylpiperidin-1-yl)-2-(trifluoromethylsulfonyloxy)quinoxaline-6-carboxylate as red oil (990 mg, crude).