[CH2:1]([O:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][C:6]=1[C:11]1[NH:16][C:15](=[O:17])[C:14]([C:18]([OH:20])=[O:19])=[CH:13][CH:12]=1)[CH2:2][CH3:3].[CH3:21]O>S(=O)(=O)(O)O.C(Cl)(Cl)Cl>[CH2:1]([O:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][C:6]=1[C:11]1[NH:16][C:15](=[O:17])[C:14]([C:18]([O:20][CH3:21])=[O:19])=[CH:13][CH:12]=1)[CH2:2][CH3:3]A stirred mixture of 6-(2-propoxyphenyl)-1,2-dihydro-2-oxopyridine-3-carboxylic acid, (0.9 g) dry methanol (30 ml) and 3 drops of concentrated sulphuric acid was heated under reflux for ca 24 hours. The cooled mixture was evaporated to yield a pale yellow solid which was dissolved in chloroform, extracted with dilute aqueous potassium carbonate (2×10 ml), washed with water and brine, dried (magnesium sulphate) and evaporated to yield a yellow solid, 0.8 g, m.p. 126°-7° C. This was recrystallised from aqueous methanol (20 ml) to yield the pure title compound, 0.65 g, m.p. 126.5°-127.5° C.
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