[Br:1][C:2]1[CH:11]=[C:10]2[C:5]([N:6](C(=O)C(F)(F)F)[C@@H:7]([CH3:19])[CH2:8][N:9]2[C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])=[CH:4][CH:3]=1.C(=O)(O)[O-].[Na+]>C(O)C>[Br:1][C:2]1[CH:11]=[C:10]2[C:5]([NH:6][C@@H:7]([CH3:19])[CH2:8][N:9]2[C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])=[CH:4][CH:3]=1A 500-mL round bottomed flask fitted with a nitrogen inlet, magnetic stir bar, and condenser was charged with (S)-tert-butyl 7-bromo-3-methyl-4-(2,2,2-trifluoroacetyl)-3,4-dihydroquinoxaline-1(2H)-carboxylate (13.10 g, 31.0 mmol), ethanol (130 mL), and half-saturated aqueous sodium bicarbonate solution (130 mL, 31.0 mmol). The reaction mixture was heated to 70° C. for 24 h and then cooled to room temperature. The ethanol was removed under reduced pressure, and the residue was extracted into dichloromethane (250 mL). The combined organic layers were concentrated under reduced pressure. The crude product was purified by column chromatography on silica gel (eluting with 4:1 hexanes-ethyl acetate) to afford (S)-tert-butyl 7-bromo-3-methyl-3,4-dihydroquinoxaline-1(2H)-carboxylate (9.78 g, 97%) as a white solid. MS (ESI, pos. ion) m/z 327, 329 [M+1]+.
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