[C:1]([O:5][C:6](=[O:20])[NH:7][CH:8]1[CH2:17][C:16]2[C:11](=[CH:12][CH:13]=[C:14]([Br:18])[CH:15]=2)[NH:10][C:9]1=[O:19])([CH3:4])([CH3:3])[CH3:2].C([O-])([O-])=O.[K+].[K+].[CH2:27](Br)[C:28]1[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=1>CC(C)=O>[C:1]([O:5][C:6](=[O:20])[NH:7][CH:8]1[CH2:17][C:16]2[C:11](=[CH:12][CH:13]=[C:14]([Br:18])[CH:15]=2)[N:10]([CH2:27][C:28]2[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=2)[C:9]1=[O:19])([CH3:4])([CH3:2])[CH3:3]A stirring mixture of 3B (0.60 g, 1.76 mmol), K2CO3 (0.49 g, 3.52 mmol), and benzyl bromide (0.36 g, 2.11 mmol) in acetone (15 mL) was heated to reflux under argon for 16 h. The mixture was then cooled to RT and the solvent was evaporated under vacuum. The resulting residue was partitioned between water and EtOAc. The EtOAc layer was washed with brine, dried (Na2SO4), and evaporated. The resulting crude product was chromatographed on silica gel eluted with 10-20% EtOAc in hexane (step-wise gradient) to obtain the title compound (0.72 g) as a solid.
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