Quinolone analogs 13: Synthesis of novel 1,1′-(2-methylenepropane-1,3-diyl)di(4-quinolone-3-carboxylate) and related compounds

The reaction of the 4-hydroxyquinoline-3-carboxylate 6 with pentaerythritol tribromide gave the 1,1′-(2-methylenepropane-1,3-diyl)di(4-quinolone-3-carboxylate) 11, whose reaction with bromine afforded the 1,1′-(2-bromo-2-bromomethylpropane-1,3-diyl)di(4-quinolone-3-carboxylate) 12. Compound 12 was transformed into the (Z)-1,1′-(2-acetoxymethylpropene-1,3-diyl)di(4-quinolone-3-carboxylate) 13 or (E)-1,1′-[2-(imidazol-1-ylmethyl)propene-1,3-diyl]di(4-quinolone-3-carboxylate) 14. Hydrolysis of the dimer (Z)-13 or (E)-14 with potassium hydroxide provided the (E)-1,1′-(2-hydroxymethylpropene-1,3-diyl)di(4-quinolone-3-carboxylic acid) 15 or (Z)-1,1′-[2-(imidazol-1-ylmethyl)propene-1,3-diyl]di(4-quinolone-3-carboxylic acid) 16, respectively. The nuclear Overhauser effect (NOE) spectral data supported that those hydrolysis resulted in the geometrical conversion of (Z)-13 into (E)-15 or (E)-14 into (Z)-16.