Electrons and Holes as Catalysts in Organic Electrosynthesis

Abstract

The injection (or removal) of electrons into (or from) a substrate by an electrode can effectively catalyze various redox‐neutral reactions that otherwise require harsh conditions and/or the use of reagents. Such processes involve the electrogeneration of an ionic or radical ionic species, which after a coupled chemical step either undergoes a backward electron exchange with the electrode (ECEb mechanism) or triggers a chain process in the bulk solution. Under these circumstances, sub‐stoichiometric amounts of charge are sufficient to achieve a full conversion and conceptionally, the electrons and holes can be understood as being catalysts. This principle has been successfully applied to accomplish a number of redox‐neutral transformations such as molecular rearrangements, Diels‐Alder‐type cycloadditions and radical substitution reactions (SRN1) in a mild and atom‐economical fashion. Although examples have been reported but sporadically since the early 1970s, a number of exciting recent developments have led us to review and discuss these cases using unifying mechanistic concepts that are described herein.

Organic Electrochemistry: Molecular Syntheses with Potential

“…It is noteworthy that the concept of modern redox mediators has proven to be beneficial for various aspects of organic electrosynthesis and innovative electrocatalysis ( vide infra ). 48 Also, novel electrode materials 49 have recently proven to have a major impact on the selectivity of specific organic electrochemical transformations. For instance, on the basis of the pioneering studies on biaryl formations in electrosynthesis, 50 recent impetus has been gained in electrooxidative coupling reactions to enable unprecedented substitution patterns and selectivity regimes, particularly by the aid of boron-doped diamond (BDD) electrodes, along with 1,1,1,3,3,3-hexafluoro-propan-2-ol (HFIP) as the solvent.…”

Electrochemically Catalyzed N–N Coupling and Ring Cleavage Reaction of 1H-Pyrazoles

“…Since only substoichiometric amounts of charge are required to achieve a full chemical transformation and conversion, the performed electrosynthesis should be carried out via electrochemically catalyzed reactions. 16 The UV-vis spectra of 3,5-DMP and 3,5-MPP were collected during the electrolyses. Although these spectra do not show the exact structure of the compounds, they indicate that the products do not exhibit absorption peaks of either their starting aromatic pyrazole rings or structures with high conjugation (Figure 2).…”

“…[4][5][6] Moreover, electrosynthesis is a valuable method for the synthesis of industrial and biological applicable compounds, especially whenever there are complex or impossible preparation processes under conventional procedures. 7,8 Thus, during the last decade, electrosynthesis [9][10][11] and electrocatalyzed synthesis [12][13][14][15][16] have become the best, attractive and effective methods for the interaction of molecules and chemical transformations in organic synthesis.…”

Electricity‐Driven Post‐Functionalization of Conducting Polymers

“…Electron transfer is a fundamental process in organic synthesis, and various synthetic protocols based on this process have been developed [1–5] . In particular, electrosynthesis is recognized as one of the most powerful and straightforward techniques to perform electron transfer‐driven reactions [6–11] . Electron transfer between a substrate and an electrode is triggered by the application of a potential to the electrode, which generates reactive intermediates.…”