engleski

Synthesis and structure of two isomeric enaminones

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-(1-naphthylamino)-2-butenoyl)-2-oxo-2H-pyran-6-carboxylate (2) and ethyl 4-(4-hydroxy-6-methyl-2-oxo-2H-pyran-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 a cyclic part (pyrone ring) and in side chain to give a variety of possible tautomeric form. 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, reinforced by pi-delocalzation, intramolecular hydrogen bonds of N-H...O and O-H...O type. The molecules as a whole are not planar exhibiting planarity in the central heteroconjugated moiety, while naphthyl rings are almost perpendicular to central part.

Enaminones; 2H-pyran-2-ones; NMR spectra; Crystal structures; Resonance

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