Phosphorus oxychloride → (S)-methyl 2-chloro-3-(2-methylpyrrolidin-1-yl)quinoxaline-6-carboxylate

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Reaction Steps

The solution of methyl 3-[(2S)-2-methylpyrrolidin-1-yl]-2-oxo-1,2-dihydroquinoxaline-6-carboxylate (5.9 g, 20.54 mmol,) in phosphorus oxychloride (100 mL) was stirred overnight at 120° C. in an oil bath. The reaction mixture was concentrated in vacuo and diluted with dichloromethane (500 mL) and ice-water (500 mL), adjusted to pH 7 with NaHCO3 solution. The solution was extracted with dichloromethane (3×200 mL) and the organic layers combined, dried over anhydrous sodium sulfate and concentrated in vacuo to give a residue, which was purified by silica gel column chromatography eluting with 2% ethyl acetate in petroleum ether to afford methyl 2-chloro-3-[(2S)-2-methylpyrrolidin-1-yl]quinoxaline-6-carboxylate as a yellow solid (5 g, 80%).

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