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Synthesis and Structure of Two Isomeric Enaminones

Ana Brbot-Saranović ; Department of Chemistry, Faculty of Veterinary Medicine, University of Zagreb, Heinzelova 55, 10000 Zagreb, Croatia
Gordana Pavlović ; Laboratory of General and Inorganic Chemistry, Faculty of Science, University of Zagreb, Zvonimirova 8, 10000 Zagreb, Croatia
Višnja Vrdoljak ; Laboratory of General and Inorganic Chemistry, Faculty of Science, University of Zagreb, Zvonimirova 8, 10000 Zagreb, Croatia
Marina Cindrić orcid.org/0000-0003-3062-9902 ; Laboratory of General and Inorganic Chemistry, Faculty of Science, University of Zagreb, Zvonimirova 8, 10000 Zagreb, Croatia

Sažetak

The reaction of ethyl 2-hydroxy-4-(4-hydroxy-6-methyl-2H-pyran-2-on-3-yl)-4-oxo-2-butenoate (1) and 1-naphthylamine in ethanol affords two isomeric enaminones: ethyl 4-hydroxy-3-[3-(1-naphthyl-amino)-2-butenoyl]-2H-pyran-2-on-6-carboxylate (2) and ethyl 4-(4-hydroxy-6-methyl-2H-pyran-2-on-3-yl)-2-(1-naphthylamino)-4-oxo-2-butenoate (3).
The structures of both compounds were determined by the single crystal X-ray diffraction. Tautomerism may be involved in two parts of a molecule, in the cyclic part (pyrone ring) and in the side chain, to give a variety of possible tautomeric forms. Attention has been turned to the endo-enol enamine and exo-enol enamine tautomeric equilibrium, since both tautomers were found in the crystals of compounds with similar structures. The NMR spectroscopic data and X-ray structural analysis confirmed that both compounds exist in the endo-enol enamine form in the solution and in the crystalline state. The molecules are characterized by strong, intramolecular hydrogen bonds of N−H⋅⋅⋅0 and O−H⋅⋅⋅O type reinforced by π-delocalization. The molecules as a whole are not planar, exhibiting planarity only in the Central heteroconjugated moiety, while naphthyl rings are almost perpendicular to the Central part.

Ključne riječi

enaminones; 2H-pyran-2-ones; NMR spectra; crystal structures; resonance assisted hydrogen bonds; structure and tautomeric isomerism

Hrčak ID:

131834

URI

https://hrcak.srce.hr/131834

Datum izdavanja:

2.4.2001.

Posjeta: 776 *