A New Strategy for the Preparation of E Isomers of Hydrazones and Anil-Like Compounds: Thermally Stimulated Isomerization of Z Isomers of Anions

A new, simple method for the preparation of E-isomers of hydrazones and anil-like compounds from Z-isomers of these compounds has been developed. In DMF, the Z-isomers of these compounds in the presence of tetrabutylammonium fluoride (TBAF) or tetrabutylammonium acetate (TBAA) gave the corresponding N anions of the Z-isomers, which are isomerized to the N anions of the E-isomers even at room temperature. Upon addition of a protic solvent (H2O, or CH3OH) to this reaction mixture, the N anion of the E-isomer was immediately quantitatively converted to the E-isomer of the corresponding nonionic compound, which can be readily isolated by methods commonly used in the synthesis.