C([O:3][C:4]([C:6]1[C:7](=[O:23])[NH:8][C:9]2[C:14]([C:15]=1[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1)=[CH:13][CH:12]=[C:11]([CH3:22])[CH:10]=2)=O)C>S(=O)(=O)(O)O>[CH3:22][C:11]1[CH:10]=[C:9]2[C:14]([C:15]3[C:16]4[C:17](=[CH:18][CH:19]=[CH:20][CH:21]=4)[C:4](=[O:3])[C:6]=3[C:7](=[O:23])[NH:8]2)=[CH:13][CH:12]=1A mixture of 1,2-dihydro-4-phenyl-7-methyl-2-oxo-3-quinoline carboxylic acid ethyl ester (2.5 g, 8.1 mmol) and conc. sulfuric acid (20 ml) was stirred with heat at 95° C. for 10 hours. The reaction mixture was poured into ice water to obtain a crystal precipitated by filtration. The crystal obtained was washed with water and methanol in this sequence to give 1.5 g (yield 70.6 of the title compound.
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