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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.
24c. 1,2,3,4-tetrahydroquinoxaline To a solution of 24b (300 mg, 1.85 mmol) in THF (2 mL) was added 1N LiAlH4 (10 mL, 10 mmol). The reaction mixture was stirred at rt for 1 h. The reaction mixture was quenched with H2O (1 mL) at 0 C., 15% NaOH (1 mL), followed by H2O (1 mL). The reaction mixture was extracted with EtOAc. The EtOAc was then washed with brine, dried over Na2SO4. The solvent was evaporated under reduced pressure to afford 24c (260 mg, 95%) as white powder. LC-MS ESI m/z 149 [M+H]+.