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 ¹³C-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).