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Structural assignment of the enol–keto tautomers of one-pot synthesized 4-hydroxyquinolines/4-quinolones

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Abstract

The one-pot preparation of 2,3-disubstituted 4-quinolones and the structural assignment of their tautomers are described. The mono-selective Michael addition of anilines to α,α-dioxoketene dithioacetals followed by thermal cyclization of the crude N,S-acetals gave the desired 4-hydroxyquinolines in good to excellent yields. The tautomeric structures of the obtained products were confirmed by X-ray crystallography, IR, and NMR experiments. Spectroscopic data revealed that the equilibrium between the enol and keto forms of the bicyclic system was determined by the strength of the internal H-bonds. A H-bond acceptor at the 3-position favored the enol form via 6-membered intramolecular H-bonding. A H-bond acceptor at the 2- or 8-position completely switched the equilibrium to favor the keto form possibly due to extended conjugation and H-bonding. The experimental assignments were perfectly matched with the results of DFT calculation.

Graphical abstract: Structural assignment of the enol–keto tautomers of one-pot synthesized 4-hydroxyquinolines/4-quinolones

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Publication details

The article was received on 16 Aug 2018, accepted on 28 Nov 2018 and first published on 28 Nov 2018


Article type: Research Article
DOI: 10.1039/C8QO00884A
Citation: Org. Chem. Front., 2019, Advance Article
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    Structural assignment of the enol–keto tautomers of one-pot synthesized 4-hydroxyquinolines/4-quinolones

    O. Kang, S. J. Park, H. Ahn, K. C. Jeong and H. J. Lim, Org. Chem. Front., 2019, Advance Article , DOI: 10.1039/C8QO00884A

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