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REACTIONS OF 3-ACYL-4-HYDROXY-2(1H)-QUINOLONES WITH NITROGEN BASES

3-Acyl-4-hydroxy-2-quinolones 1 react with amines to yield 3-aminomethylene quinolinediones 2. With hydroxylamine the corresponding oximes 3 are obtained, which cyclize on heating via a thermal Beckmann rearrangement to oxazolo[5,4-c]quinolones 4. The oxazoles can be ringopened in the presence of acids to give 3-acylamino-4-hydroxyquinolones 5. The hydrazones 6, obtained from 3-acyl-4-hydroxy-2-quinolones 1 and hydrazines, cyclize either to pyrazolo[4,3-c]quinolones 7 or give mixtures of 7 and the dimeric azino-diethylidenequinolones 8. INTRODUCTION 4-Hydroxy-2-quinolines, their oxygen derivatives and the monocyclic debenzo derivatives having aliphatic acyl groups in position 3 have found great interest in the last years because of their biological properties (4). Reaction of the keto group of this class of compounds with nitrogen bases such as amines, hydroxylamines and hydrazines offers an entry to nitrogen containing carbonyl derivatives. Some of them have caused great interest because of their biological (5) or technical properties (6). RESULTS AND DISCUSSION We have shown recently, that 3-acyl-4-hydroxyquinolones of type 1 could be aminated in an equilibrium process at the keto moiety of the 3-acyl substituent by reaction with aqueous ammonia or amines with acetic acid as catalyst (7). The isomeric 4-amino-3-acylquinolones could be excluded by synthesis of the corresponding compounds via an independent pathway. Aliphatic and aromatic amines could be shown to react with 1a-f in ethanol as solvent also by using dimethylaminopyridine as basic catalyst to obtain the 4-hydroxy-3-iminoethyl-2-quinolones 2a-l in good yields. H NMR spectroscopic studies have shown that compounds of this type deriving from 3-carbaldehydes (instead of 3-acyl groups in 2) exist mainly in the tautomeric enaminoketone form (8) by using the aldehydic/olefinic proton as probe. The lack of this proton in 2 does not allow a similar assignment, and the carbonyl frequencies of the 4-oxo group in infrared spectra, which are usually a good hint for discussion of tautomers (9), are not helpful because of hydrogen bondings between the 4-hydroxy/4-oxo group with the imino/amino group, resp. Investigations by deuterium isotope effects on C NMR chemical