Trifluoroacetic acid → 4-Chloro-2-isobutylimidazo[1,2-a]quinoxaline

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To a solution of the 2-(3-chloroquinoxalin-2-ylamino)-4-methylpentanal (1.03 g, 3.71 mmol) in 8 mL of trifluoroacetic anhydride was added 0.2 mL trifluoroacetic acid at room temperature. The reaction mixture was stirred at that temperature overnight. The solvents were removed under reduced pressure. And then 20 mL of saturated aqueous sodium bicarbonate was added. The resulting mixture was extracted with ethyl acetate (50 mL×3). The combined organic layers were washed with water (20 mL), brine (20 mL), dried over MgSO4, filtered and concentrated. The crude product was purified by flash column chromatography eluted with ethyl acetate and hexanes to give the titled compound (630 mg, 65%). MS: MH+=260:262=3:1. 1H NMR (300 MHz, CDCl3): δ 8.05 (m, 1H), 7.93 (s, 1H), 7.86 (m, 1H), 7.67 (m, 1H), 7.59 (m, 1H), 2.87 (d, 2H), 2.17 (m, 1H), 1.02 (d, 6H).

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