* All experimental methods are cited from the reference, please refer to the original source for details. We do not guarantee the accuracy of the content in the reference.
With bis-triphenylphosphine-palladium(II) chloride In toluene at 20 - 90℃;
To a degassed stirred solution of 6-bromo quinoxaline (2.0 g, 9.50 mmol) in toluene (20 mL), 1- ethoxy vinyl tributyltin (3.8 g, 10.5 mmol) followed by Pd(PPh3)2CI2 (0.67 g, 0.95 mmol) were added at RT and stirred at 90 °C overnight. After completion of the reaction (monitored by TLC), the reaction mixture was cooled to RT, filtered through celite and the obtained filtrate was evaporated under vacuum. To the resulting crude mixture, 6 N HCI solution (20 mL) was added and the mixture was stirred at RT for 1 h. The solution was neutralized with sat. NaHC03 and the aqueous layer was extracted with DCM (2 x 100 mL). The combined organic layer was dried over Na2S04 and concentrated under vacuum. The resulting crude material was purified by flash chromatography (Biotage Isolera, eluent: 30percent EtOAc in hexane) to afford the title compound. Yield: 45percent (800 mg, brown solid). 1H NMR (400 MHz, DMSO-tf6): δ 9.06-9.04 (m, 2H), 8.70 (d, J = 2.4 Hz, 1 H), 8.28 (dd, J = 8.8, 2.8 Hz, 1 H), 8.16 (d, J = 8.4 Hz, 1 H), 2.97 (s, 3H). LCMS: (Method A) 173 (M+H), Rt. 2.2 min, 99.1 percent (Max).
With bromine In acetonitrile for 2.5 h; Reflux; Inert atmosphere
General procedure: Bromine was added dropwise to a magnetically stirred refluxing solution of quinoxaline (1) or tetrahydroquinoxaline 15 or 19 in the relevant solvent. The resulting reaction mixture was heated at reflux temperature. The reaction was monitored by TLC or 1H NMR spectroscopy. After the desired time, the resulting reaction mixture was allowed to cool to room temperature and the solvent was removed under reduced pressure. The mixture was diluted with a saturated solution of sodium carbonate (10mL) and the mixture was extracted with ethyl acetate (2×25mL). Combined organic layers were washed with water, dried over Na2SO4 and concentrated. The crude was purified appropriate method described in below.