General procedure for the synthesis of 7-bromo-5-fluoroquinoxaline from 2,3-dihydroxy-1,4-dioxane and 5-bromo-3-fluorobenzene-1,2-diamine: 4.00 g (19.509 mmol) of 5-bromo-3-fluorobenzene-1,2-diamine was dissolved in 100 mL of ethanol and 2.42 g (19.509 mmol) of 2,3-dihydroxy-1,4 -dioxane. The reaction mixture was stirred at room temperature for 4 hours, followed by the addition of 2.42 g (19.509 mmol) of 2,3-dihydroxy-1,4-dioxane again. After continued stirring at room temperature for 24 h, the reaction mixture was concentrated using a rotary evaporator. The residue was purified by silica gel column chromatography with dichloromethane/methanol (30:1, v/v) as eluent. Finally, 3.60 g (80% yield) of the target product 7-bromo-5-fluoroquinoxaline was obtained.LC-MS (Method 1): retention time (R t) = 1.79 min; mass spectrum (EIpos): m/z = 227 [M + H]+.1H-NMR (400 MHz, DMSO-d6): δ (ppm) = 8.06 (dd, 1H), 8.24 ( t, 1H), 9.05 (d, 1H), 9.07 (d, 1H).
