Phosphorus oxychloride → 2-(1-Bromoethyl)-3-chloro-6-fluoroquinoxaline

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A heterogeneous mixture of 3-(1-bromoethyl)-7-fluoroquinoxalin-2(1H)-one (58.86 g, 217.1 mmol) and phosphorous oxychloride (198.8 ml, 2171 mmol) in a 1 L round bottom flask was stirred at 100° C. for 2 h. The mixture was heterogeneous in the beginning of the reaction and then homogeneous black solution over 1 h. After 2 h, the mixture was cooled to rt and concentrated under reduced pressure. To the black residue was carefully added ice (˜400 ml) in portions and then water (200 ml) with stirring. The mixture was neutralized with NH4OH (200 ml) and ice (˜200 ml) with stirring. The resulting precipitate was collected by filtration, rinsed with water (1 L), and dried under high vacuum overnight to give 2-(1-bromoethyl)-3-chloro-6-fluoroquinoxaline (58.31 g, 92.8% yield) including 3-chloro-2-(1-chloroethyl)-6-fluoroquinoxaline as a brown solid. 1H NMR (400 MHz, DMSO-d6), ratio of bromoethyl analog and chloroethyl analog=2.5:1 Mass Spectrum (ESI) m/e=288.9 [M+H(79Br)]+ and 291.0 [M+H (81Br)]+

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