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To a stirred solution of 1-(3-(cyclopropylamino)-6-fluoro-2-methylquinoxalin-5-yl)ethanone (283b) (1.44 g, 5.55 mmol) in DCM (13.88 mL) at 0° C. was added TEA (0.91 mL, 6.54 mmol) and tert-butyldimethylsilyl trifluoromethanesulfonate (Sigma-Aldrich) (1.40 mL, 6.11 mmol). The overall mixture was stirred at 0° C. for 1 h, while under inert atmosphere. The reaction mixture was treated with saturated NaHCO3 (20 mL) and the layers were separated. The aq. layer was extracted with DCM (3×). The combined organic extracts were dried over Na2SO4, filtered and concentrated in vacuo. m/z (ESI, +ve) 374 (M+H). The residue was treated with THF (13.88 mL) and water (1.6 mL). The resulting mixture was chilled to 0° C. in an ice/water bath. NBS (Alfa Aesar, Ward Hill, Mass.) (0.99 g, 5.55 mmol) was added into the mixture and the overall mixture was stirred at 0° C. for 30 min. The mixture was diluted with DCM (40 mL) and saturated NaHCO3 (10 mL). The layers were separated and the aq. layer was extracted with DCM (3×). The organic extracts were combined, dried over Na2SO4, filtered and concentrated in vacuo. The crude material was purified by chromatography through a SiliCycle SiliaSep pre-packed silica-gel column (120 gram), eluting with a gradient of 0-25% EtOAc in DCM, to provide 2-bromo-1-(3-(cyclopropylamino)-6-fluoro-2-methylquinoxalin-5-yl)ethanone (283c) (1.19 g, 3.52 mmol, 63% yield) as light yellow solid. 1H NMR (400 MHz, DMSO-d6) δ ppm 7.94 (dd, J=9.00, 5.87 Hz, 1H), 7.65-7.84 (m, 1H), 7.32 (t, J=9.39 Hz, 1H), 5.18 (s, 2H), 2.69-2.91 (m, 1H), 2.51 (s, 3H), 0.76-0.95 (m, 2H), 0.60-0.76 (m, 2H). m/z (ESI, +ve) 338/341 (M+H).

1. customthe layers were separated
2. extractionThe aq. layer was extracted with DCM (3×)
3. dry with materialThe combined organic extracts were dried over Na2SO4
4. filtrationfiltered
5. concentrationconcentrated in vacuo
6. additionThe residue was treated with THF (13.88 mL) and water (1.6 mL)
7. temperatureThe resulting mixture was chilled to 0° C. in an ice/water bath
8. stirringthe overall mixture was stirred at 0° C. for 30 min
9. customThe layers were separated
10. extractionthe aq. layer was extracted with DCM (3×)
11. dry with materialdried over Na2SO4
12. filtrationfiltered
13. concentrationconcentrated in vacuo
14. customThe crude material was purified by chromatography through a SiliCycle SiliaSep pre-packed silica-gel column (120 gram)
15. washeluting with a gradient of 0-25% EtOAc in DCM