E/Z(C=C)-Isomerization of enamines of 3-formyl-4-hydroxycoumarin induced by organic solvents

Abstract

According to 1? and 13? NMR data, enamines of 3-formyl-4-hydroxycoumarin exist in the keto enamine tautomeric form and undergo Z/E-isomerization around the C=C bond in CDCl3, DMSO-d6, and CD3OD at room temperature. The activation energies of ?/Z-isomerization were measured experimentally and calculated by the B3LYP/6-311++G(d,p) method. An X-ray diffraction study showed that 3-(benzyliminomethyl)chromane-2,4-dione in the crystalline state exists as a mixture of two keto enamine isomers.