Diethyl Oxalate → 6,7-Difluoroquinoxaline-2,3(1H,4H)-dione

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The title compound (Sarges, R. et al., J. Med. Chem. 33.2240 (1990)) was prepared using an adaptation of the method of Cheeseman. (Cheeseman, G. W. H. J. Cam. Soc. 1171 (1962)). A mixture of diethyl oxalate (1.11 g, 7.63 mmol and 4,5-difluoro-1,2-diaminobenzene (110 mg, 0.763 mmol) was heated to reflux under N2 for 2 h. The reaction was allowed to cool to room temperature and the solid was collected by vacuum filtration, rinsed with hexanes, and air dried. This gray brown solid was recrystallized from 20 mL of EtOH and the brown-white crystals collected by vacuum filtration and the crystals further dried under vacuum (0.5 torr, 25° C.) to yield 45.3 mg (30.0%); mp >360° C. (lit. >310° C.); 1H NMR (d6-acetone) δ 7.19 (t, 2H, ArH, JH-F=9.3), 10.9 (br s, 2H, NH).

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