Oxidation of quinolones with peracids (an in situ EPR study)

4‐Oxoquinoline derivatives (quinolones) represent heterocyclic compounds with a variety of biological activities, along with interesting chemical reactivity. The quinolone derivatives possessing secondary amino hydrogen at the nitrogen of the enaminone system are oxidized with 3‐chloroperbenzoic acid to nitroxide radicals in the primary step while maintaining their 4‐pyridone ring. Otherwise, N‐methyl substituted quinolones also form nitroxide radicals coupled with the opening of the 4‐pyridone ring in a gradual oxidation of the methyl group via the nitrone–nitroxide spin‐adduct cycle. This was confirmed in an analogous oxidation using N,N‐dimethylaniline as a model compound. N‐Ethyl quinolones in contrast to its N‐methyl analog form only one nitroxide radical without a further degradation. Copyright © 2013 John Wiley & Sons, Ltd.