[C:1]([C:4]1[CH:5]=[C:6]2[C:11](=[CH:12][CH:13]=1)[N:10]=[C:9]([CH3:14])[CH:8]=[CH:7]2)([OH:3])=[O:2].OS(O)(=O)=O.[CH3:20]O>>[C:1]([C:4]1[CH:5]=[C:6]2[C:11](=[CH:12][CH:13]=1)[N:10]=[C:9]([CH3:14])[CH:8]=[CH:7]2)([O:3][CH3:20])=[O:2]To a solution of 6-carboxy-2-methyl quinoline in MeOH (600 ml) was added concentrated H2SO4 and stirred for 3 days at room temperature. The reaction mixture was evaporated and the residue was diluted with H2O (250 ml) and ethyl acetate (250 ml), and transferred to a separatory funnel. A solution of saturated sodium bicarbonate in water (1 L) was added and extraction with ethyl acetate afforded a purple solid which was chromatographed on column of flash silica gel using hexane-ethyl acetate (2:1) as eluant to provide the title compound as a yellow solid: m.p. 98-101° C.
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