4-Hydroxy-2-quinolones 137. Synthesis, structure, and spectroscopic characteristics of diethyl 2,2′-dioxo-1,2,3,4,1′,2′,3′,4′-octahydro[4,4′]biquinolinyl-3,3′-dicarboxylate
Treatment of the ethyl esters of 1-R-4-chloro-2-oxo-1,2-dihydroquinoline-3-carboxylic acids with zinc dust in glacial acetic acid gives high yields of diethyl 2,2′-dioxo-1,2,3,4,1′,2′,3′,4′-octahydro[4,4′]biquinolinyl-3,3′-dicarboxylates. The structural features of the synthesized compounds together with their NMR and mass spectra are discussed.