Abstract
An efficient and straightforward synthesis of novel (Z/E)-3-[(heteroarylamino)methylidene]chromane-2,4-dione derivatives via a one-pot three-component condensation of 4-hydroxycoumarin, triethyl orthoformate, and heteroaryl amines in the presence of guanidinium chloride as organocatalyst under solvent-free conditions is described. Investigation of spectroscopy data indicated that coumarin enamines exist in the ketoenamine tautomeric form and undergo Z/E-isomerization in respect to the C=C bond in CDCl3 and DMSO-d6 at room temperature. Furthermore, intramolecular hydrogen bonds have been observed in the synthesized compounds. Also, 1H NMR spectra indicated that E-ketoenamines are the major isomers. High to excellent yields, short reaction times, simple workup, and very easy purification of products by non-chromatographic methods are advantages of this synthetic procedure.
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