[C:1]([C:4]1[CH:13]=[C:12]([OH:14])[C:11]2[C:6](=[CH:7][CH:8]=[CH:9][CH:10]=2)[N:5]=1)([OH:3])=[O:2].C(=O)([O-])[O-].[Cs+].[Cs+].[CH2:21](Br)[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1>CN(C=O)C>[CH2:21]([O:2][C:1]([C:4]1[CH:13]=[C:12]([O:14][CH2:12][C:11]2[CH:6]=[CH:7][CH:8]=[CH:9][CH:10]=2)[C:11]2[C:6](=[CH:7][CH:8]=[CH:9][CH:10]=2)[N:5]=1)=[O:3])[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=12-carboxy-4-hydroxyquinoline (5 g, 1.0 eq) was dissolved in 50 mL DMF. Cesium carbonate (20 g, 2.3 eq) was added to the solution and the resulting reaction mixture was heated at 50° C. for 20 minutes. Benzyl bromide (10 g, 2.1 eq) was added. The resulting reaction mixture was stirred at 50° C. for 1 hour. Then the reaction mixture was poured into 500 mL ice-water, the precipitate was collected by filtration, and dried in vacuo to afford 2-benzyloxycarbonyl-4-benzyloxyquinoline (9.1 g). 2-benzyloxycarbonyl-4-benzyloxyquinoline (9.0 g) was dissolved in 50 mL THF, and 2 N LiOH solution (20 mL) was added, and the resulting reaction mixture was stirred at ambient temperature for 2 hours. The solvent was then removed in vacuo, and the residue acidified by the addition of 2N NaHSO4 to pH 3–4. The white precipitate was collected to afford 2-carboxy-4-benzyloxyquinoline (7.2 g), which was used without further purification.
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