[CH:1]([C:3]1[CH:4]=[C:5]2[C:10](=[CH:11][CH:12]=1)[N:9]=[C:8]([C:13]([O:15][CH3:16])=[O:14])[C:7]([CH3:17])=[CH:6]2)=[O:2].CC(=CC)C.P([O-])(O)(O)=[O:24].[Na+].[Cl-].[Na+].Cl>O.C(O)(C)(C)C>[CH3:16][O:15][C:13]([C:8]1[C:7]([CH3:17])=[CH:6][C:5]2[C:10](=[CH:11][CH:12]=[C:3]([C:1]([OH:24])=[O:2])[CH:4]=2)[N:9]=1)=[O:14]To a mixture of water (0.8 ml) and tert-butyl alcohol (3 ml) were added methyl 6-formyl-3-methylquinoline-2-carboxylate (140 mg) , 2-methyl-2-butene (190 mg) and sodium dihydrogenphosphate (105 mg) in water bath. To the mixture was added dropwise sodium chloride (244 mg) and the mixture was stirred for 1 hour at the same temperature. The reaction mixture was cooled in an ice bath, adjusted to pH 4 with 1M hydrochloric acid and extracted with dichloromethane. The organic layer was dried over magnesium sulfate and evaporated in vacuo. The residue was purified by preparative thin-layer chromatography (dichloromethane:methanol=10:1, V/V) followed by crystallization from methanol-isopropyl ether to give 2-methoxycarbonyl-3-methylquinoline-6-carboxylic acid (121 mg) as crystals.
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