Umpolung - The “Flow” from Oxidation to Reduction. A journey from cathodic carbon-carbon bond coupling reactions carried out in a flow reactor to the electrooxidative and photoreductive characteristics of phenanthroimidazole mediators.
Electroorganic synthesis has become an established, useful, and environmentally benign alternative to classic organic synthesis for the oxidation and the reduction of organic compounds. Electric current replaces toxic redox reagents, and the overall energy consumption may be reduced. , Electroorganic chemistry provides convenient access to the chemistry of radical ions. Its unique ability to effect charge reversal (umpolung) makes it possible to achieve bond constructions that are otherwise very difficult to accomplish.
The use of redox mediators to achieve a so-called “indirect electrolysis” offers many advantages compared to a direct electrolysis. A new class of redox mediator based on triarylimidazole framework was developed in our group and later further modified to a framework based on phenathroimidazole to achieve improved redox reversibility. These mediators undergo one electron oxidization at the anode to form a radical cation, and serve as oxidative catalysts. We also explored the potential of the mediators to serve as photocatalysts in reductive processes. Both dehalogenation of aromatics and reductive cyclization reactions have been investigated and will be discussed.
In addition, a microflow reactor designed for the cathodic coupling was studied. Utilizing the flow reactor, the supporting electrolyte used was reduced by 450-fold, which made the process more environmentally friendly and cost efficient.