[NH2:1][C:2]1[C:7]([C:8]([O:10][CH3:11])=[O:9])=[C:6]([NH:12][S:13]([C:16]2[CH:21]=[CH:20][C:19]([F:22])=[CH:18][C:17]=2[Br:23])(=[O:15])=[O:14])[CH:5]=[CH:4][C:3]=1[C:24]1[CH:28]=[CH:27][O:26][C:25]=1[C:29]([O:31]CC)=O.C(=O)([O-])[O-].[K+].[K+]>CO>[Br:23][C:17]1[CH:18]=[C:19]([F:22])[CH:20]=[CH:21][C:16]=1[S:13]([NH:12][C:6]1[C:7]([C:8]([O:10][CH3:11])=[O:9])=[C:2]2[C:3]([C:24]3[CH:28]=[CH:27][O:26][C:25]=3[C:29](=[O:31])[NH:1]2)=[CH:4][CH:5]=1)(=[O:15])=[O:14]A mixture of ethyl 3-[2-amino-4-(2-bromo-4-fluorobenzenesulfonylamino)-3-methoxycarbonylphenyl]-furan-2-carboxylate (Intermediate 88, 0.960 g) and potassium carbonate (0.736 g) in methanol (50 mL) was heated at reflux overnight. The resultant mixture was concentrated in vacuo and the residue was acidified with 1M HCl and extracted with a mixture of DCM and ethyl acetate. The precipitate from the acidification did not dissolve, therefore the volatiles were removed in vacuo and the aqueous slurry was filtered. The resultant paste was triturated with hot acetonitrile and the solid was collected by filtration and dried under vacuum overnight. The resultant solid was purified by chromatography on silica, eluting with a mixture of ethyl acetate and DCM, with a gradient of 0-100%, followed by methanol and DCM, with a gradient of 0-10% and finally flushing the column with methanol and DCM (50%) to give methyl 7-(2-bromo-4-fluorobenzenesulfonylamino)-4-oxo-4,5-dihydrofuro[2,3-c]quinoline-6-carboxylate (0.685 g).
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