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

Abstract

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.

Photochemical cyclopropanation in aqueous micellar media – experimental and theoretical studies

“…the diazo reagent, generated in the reaction is the same, we can expect some differences in the reactivity between the E - and Z -hydrazones as their stability vary and thus their propensity for deprotonation is different. 40 Also, the two isomers may position themselves differently in the micelle to enable favourable electrostatic interactions and hydrogen bonding, thus influencing the rate of carbene generation. 9 Thus, E - and Z -hydrazones 4b were evaluated; the E -hydrazone performed better by about 20% in terms of yield and the diastereoselectivity was significantly improved to 1 : 20, whereas the Z -hydrazone provided 1 : 8 dr.…”