4-hydroxy-2-quinolones. 43. Thermolysis of ethyl esters of 1-R-2-oxo-4-hydroxy-quinoline-3-carboxylic acids

Ethyl esters of 1-R-2-oxo-4-hydroxyquinoline-3-carboxylic acids under thermolysis conditions are converted to 5,9-di-R-6,7,8-trioxodiquinolino[3,4-b;3′,4′-e]-4H-pyrans. One of the synthesized compounds was studied by X-ray diffraction.