[OH:1][C:2]1[CH:7]=[CH:6][C:5]([CH2:8][N:9]2[C:13]3[CH:14]=[CH:15][CH:16]=[CH:17][C:12]=3[N:11]([C:18]([O:20][CH2:21][CH3:22])=[O:19])[C:10]2=[O:23])=[CH:4][C:3]=1[CH2:24][CH2:25][CH3:26].C(=O)([O-])[O-].[Cs+].[Cs+].Br[CH:34]([C:40]1[CH:45]=[CH:44][C:43]2[O:46][CH2:47][O:48][C:42]=2[CH:41]=1)[C:35]([O:37][CH2:38][CH3:39])=[O:36]>CN(C=O)C.C(O)(=O)CC(CC(O)=O)(C(O)=O)O>[C:35]([CH:34]([C:40]1[CH:45]=[CH:44][C:43]2[O:46][CH2:47][O:48][C:42]=2[CH:41]=1)[O:1][C:2]1[CH:7]=[CH:6][C:5]([CH2:8][N:9]2[C:13]3[CH:14]=[CH:15][CH:16]=[CH:17][C:12]=3[N:11]([C:18]([O:20][CH2:21][CH3:22])=[O:19])[C:10]2=[O:23])=[CH:4][C:3]=1[CH2:24][CH2:25][CH3:26])([O:37][CH2:38][CH3:39])=[O:36]To a solution of 0.105 g (0.30 mmol) of the product of step C in 1.0 mL of DMF was added 0.115 g (0.33 mmol) of cesium carbonate and the resulting suspension was stirred under a nitrogen atmosphere for 15 minutes. A solution of 0.094 g (0.33 mmol) ethyl α-bromo-3,4-methylenedioxyphenylacetate in 0.5 mL of DMF was then added and the reaction mixture was stirred at room temperature overnight. The reaction mixture was then suspended in 10% aqueous citric acid and extracted into ethyl acetate. The organic layer was separated, washed with saturated sodium bicarbonate, brine, dried (MgSO4), filtered and evaporated. The residue was purified on a silica gel flash chromatography column eluted with 30% EtOAc-hexane; combination of the product fractions and evaporation in vacuo afforded 0.137 g (83%) of the title compound.
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