Abkömmlinge der 3‐Chinolincarbonsäure mit Sauerstoffsubstitution in Stellung 4, 5 and 8: Synthese, Reaktionen, NMR.‐Studien

Derivatives of 3‐Quinolinecarboxylic Acid with Oxygen Substitution in Positions 4, 5 and 8: Synthesis, Reactions, NMR. Studies Starting from either 1, 4‐dibenzyloxybenzene (7) or 2, 5‐dimethoxyaniline ( 16 ), synthetic routes have been developed to benzenoid and quinoid derivatives of 4‐oxo‐1, 4‐dihydro‐3‐quinolinecarboxylic acid with O‐bearing substituents in the positions 5 and 8 (compounds 12 ‐ 15 , 19 , 20 , 23 , and 24 ). With the 1‐ethyl‐4, 5, 8 trioxo acid 14 as a dienophile, a series of linear tricyclic diene adducts ( 29 ‐ 32 ) has been prepared, the structures of which were further modified by aromatization, reduction or dehydrogenation (compounds 33 ‐ 40 ). A series of benzenoid and quinoid compounds with an additional substituent in position 6 or 7 ( Table 1 ) has been derived mainly from the quinone 14 , primarily by addition of nucleophiles and eventually subsequent steps, and by aromatic electrophilic substitution of the 1‐ethyl‐5, 8‐dimethoxy acid 23 . The substitution pattern of some of these compounds has been elucidated by detailed 13 C‐NMR. studies ( Table 2 ) and/or nuclear Overhauser ‐effect studies ( Table 3 ). Correlations, based essentially on chemical arguments, allowed to define the structures of most of the residual new compounds ( Table 4 ).