[CH3:1][O:2][CH2:3][CH:4]([N:8]1[C:17]2[C:12](=[CH:13][C:14]([I:18])=[CH:15][CH:16]=2)[C:11](=[O:19])[C:10]([C:20]([O:22]CC)=[O:21])=[CH:9]1)[CH2:5][O:6][CH3:7].[OH-].[Li+]>O1CCCC1.O>[CH3:1][O:2][CH2:3][CH:4]([N:8]1[C:17]2[C:12](=[CH:13][C:14]([I:18])=[CH:15][CH:16]=2)[C:11](=[O:19])[C:10]([C:20]([OH:22])=[O:21])=[CH:9]1)[CH2:5][O:6][CH3:7]Ethyl 1-(1,3-dimethoxypropan-2-yl)-6-iodo-4-oxo-1,4-dihydroquinoline-3-carboxylate (Intermediate 22, 270 mg, 0.60 mmol) was dissolved in tetrahydrofuran (20 mL) and water (5 mL). Lithium hydroxide (56 mg, 2.42 mmol) was added and the mixture was stirred for 10 min at room temperature. The reaction mixture was then refluxed at 80° C. for 1 h. The reaction mixture was concentrated under reduced pressure and water (10 mL) was added. The pH was adjusted to 2 with hydrochloric acid (2N) and the solid that precipitated was collected by filtration and dried to afford 185 mg (75%) of 1-(1,3-dimethoxypropan -2-yl)-6-iodo-4-oxo-1,4-dihydroquinoline-3-carboxylic acid.
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