[C:1]([O:5][C:6]([CH:8]1[CH2:14][CH2:13][C:12]2[CH:15]=[CH:16][C:17]([O:19][CH3:20])=[CH:18][C:11]=2[N:10]([CH2:21][CH3:22])[C:9]1=[O:23])=[O:7])([CH3:4])([CH3:3])[CH3:2].BrN1C(=O)CCC1=O>C(Cl)(Cl)Cl>[C:1]([O:5][C:6]([CH:8]1[CH:14]=[CH:13][C:12]2[CH:15]=[CH:16][C:17]([O:19][CH3:20])=[CH:18][C:11]=2[N:10]([CH2:21][CH3:22])[C:9]1=[O:23])=[O:7])([CH3:4])([CH3:3])[CH3:2]A mixture of 3(R,S)-tert-butoxycarbonyl-1-ethyl-8-methoxy-2,3,4,5-tetrahydro-1H-1-benzazepine-2-one (0.80 g, 2.51 mmol) and N-bromosuccinimide (0.49 g, 2.76 mmol) in chloroform (20 mL) was heated at reflux for 5 hrs. The resulting reaction mixture was washed with saturated aqueous solution of NaHCO3 and water, dried over anhydrous Na2SO4, filtered and evaporated to dryness. The crude product was purified by flash chromatography on silica gel column eluted with EtOAc/n-hexane (3:7). The fractions containing the fast running component were collected and evaporated to dryness. The desired compound (60 mg, 8%) was obtained as a white crystalline powder.
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