Design, Synthesis And Application Of Triarylimidazole Derivatives As Electrochemical Organic Redox Catalysts

Indirect electrochemical oxidation has been widely studied for its advantages todirect electrooxidation. The discovery and application of a novel organic redoxcatalyst will be discussed herein.Triarylimidazole, a new organic redox catalyst has been synthesized, and itselectrochemical properties have been analyzed. Furthermore, its application to organicreactions has been investigated. The main research results are as follows:(1) Design and synthesis of triarylimidazole redox mediatorsA series of triarylimidazoles was synthesized and characterized electrochemically.The synthetic route is general, purification is simple, and the yield is excellent. Mostimportantly, it provides a pathway to over30redox mediators that exhibit a>700mVrange of accessible potentials, which is dependent upon the electronic character of thesubstituents appended to the aromatic rings. Finally, triarylimidazoles are readilysolubilized in organic solvents, having a broad and divinable oxidation potential.(2) The application of triarylimidazole mediators in electrooxidative C-HactivationThe application of triarylimidazole as an electron transfer agent (mediators) hasbeen investigated. In particular, the electrochemically mediated oxidation of benzylalcohol in the presence of excess base was examined. Catalytic current can beobserved clearly by cyclic voltammetry (CV). Based on this result, preparative scaleelectrolysis of a series of primary and secondary benzylic alcohols and asymmetricbenzyl oxide was performed using the triarylimidazole mediator, transforming them toaldehydes, ketones and esters, respectively.(3) The application of triarylimidazole mediators to tandem ring-opening/Friedel-Crafts alkylation reactionsTo further explore the utility of triarylimidazoles as redox mediators, a tandemring-opening/Friedel-Crafts alkylation reaction of chalcone epoxide was studied. Theoxidation potential of the starting material and the properties of the nucleophile wereexamined. Chiral α-hydroxy ketones, containing furan, pyrrole and indole groups,were synthesized. The tandem reaction required only catalytic amounts of current.