Green synthesis of new lawsone enaminones and their Z/E(CC)-isomerization induced by organic solvent

Abstract

The synthesis of a new class of lawsone enaminone derivatives by using lawsone, triethyl orthoformate and aromatic amines in the presence of guanidinium chloride under solvent-free conditions has been developed. Investigation of ¹H-NMR spectra indicated that lawsone enaminones exist in the ketoenamine tautomeric form and undergo Z/E-isomerization with respect to the CC bond in DMSO-d₆ at room temperature. Furthermore, intramolecular hydrogen bonds have been observed in the synthesized compounds. This method has some advantages including short reaction times, high to excellent yields, simple work-up procedure and very easy purification of products by non-chromatographic methods.