Electrochemical Arylation Reaction

Abstract

Arylated products are found in various fields of chemistry and represent essential entities for many applications. Therefore, the formation of this structural feature represents a central issue of contemporary organic synthesis. By the action of electricity the necessity of leaving groups, metal catalysts, stoichiometric oxidizers, or reducing agents can be omitted in part or even completely. The replacement of conventional reagents by sustainable electricity not only will be environmentally benign but also allows significant short cuts in electrochemical synthesis. In addition, this methodology can be considered as inherently safe. The current survey is organized in cathodic and anodic conversions as well as by the number of leaving groups being involved. In some electroconversions the reagents used are regenerated at the electrode, whereas in other electrotransformations free radical sequences are exploited to afford a highly sustainable process. The electrochemical formation of the aryl-substrate bond is discussed for aromatic substrates, heterocycles, other multiple bond systems, and even at saturated carbon substrates. This survey covers most of the seminal work and the advances of the past two decades in this area.

Electrochemical Flash Fluorination and Radiofluorination

“…TFE, tetrabutylammonium perchlorate (TBAP) and triflic acid were used in the cathodic chamber. 1,1,1,3,3,3‐Hexafluoroisopropanol (HFIP) has also recently been reported as a solvent for electroorganic synthesis with a stabilizing effect on carbocation intermediates . However, yields were negligible due to instability of fluorinated products reported here in HFIP.…”

Direct Metal‐ and Reagent‐Free Sulfonylation of Phenols with Sodium Sulfinates by Electrosynthesis

“…A simple galvanostatic mode of operation in an undivided electrolysis cell ensures scalability and an easy, rapid performance. These characteristics, supplemented by the use of water in the solvent, provides this protocol the attributes of green chemistry …”

“…As a strong hydrogen‐bridge donor, HFIP is able to stabilize radical and cationic intermediates by solvation . In addition, HFIP is a low‐electron compound and is characterized by the fact that substances with an increased electron density are more strongly solvated, whereby a decoupling of oxidation potential and nucleophilicity can be ensured . These advantages lead to supply selective coupling products for anodic conversions .…”

Electrochemical Pinacol Coupling of Acetophenone Using Boron‐Doped Diamond Electrode

“…Among the known carbon‐based electrodes, conductive boron‐doped diamond (BDD) where boron is substituted with carbon shows the outstanding electrochemical properties: wide potential window especially in aqueous media, low background current, chemical and physical stability, and others . Electrosynthesis using the BDD electrode provides some unique molecular transformations: efficient generation of methoxy radicals in methanol and the addition reaction, and extremely selective aryl‐aryl coupling reactions using 1,1,1,3,3,3‐hexafluoroisopropanol as solvent . It should be noted that the BDD electrode enables cathodic reduction of CO 2 and oximes, the reductive coupling of cinnamates, and the reductive formation of nitrones …”