Moderne Aspekte der Elektrochemie zur Synthese hochwertiger organischer Produkte

Abstract

Die stoffliche Nutzung von Elektrizität anstelle stöchiometrischer Mengen an Oxidations‐ oder Reduktionsmitteln ist ökonomisch und ökologisch sehr attraktiv und stellt eine wichtige Triebkraft für die Forschungen in der Elektrosynthese dar. Um den Elektronentransfer an der Elektrode für eine organische Umsetzung zu nutzen, müssen die intermediär gebildeten Radikalspezies stabilisiert werden. Die Kombination der Elektrosynthese mit anderen Ansätzen der organischen Chemie oder aktuellen Synthesekonzepten ermöglicht die Entwicklung effizienter Synthesewege. Die zentrale Aufgabe des 21. Jahrhunderts besteht darin, möglichst wenig fossilen Kohlenstoff zu verwenden, weshalb die Nutzung erneuerbarer Energien immer wichtiger wird. Von steigendem Interesse ist auch die direkte Umsetzung erneuerbarer Rohstoffe, die zuvor hauptsächlich verbrannt wurden. Dieser Aufsatz gibt einen Überblick über viele der wichtigsten, zukunftsweisenden Entwicklungen der letzten Zeit, welche die Zukunft dieses sich rasch entwickelnden Feldes bestimmen werden.

Electrooxidative Ruthenium‐Catalyzed C−H/O−H Annulation by Weak O‐Coordination

“…Electrosynthesis has emerged as an increasingly powerful tool for molecular syntheses. [1] Recently,s ignificant momentum was gained by the merger of electrocatalysis with organometallic [2] CÀHa ctivation. [3] However,d espite these indisputable advances,a ll electrochemical CÀHa ctivation reactions [4] are thus far limited to palladium [3] and cobalt [5] catalysts, [1b] and are severely restricted by substrates bearing nitrogen-containing,s trongly coordinating directing groups.…”

Elektrifizierung der organischen Synthese

“…This concept will be surveyed in detail in af ollow-up Review on electrochemical methods. [173] It should be noted that unactivated arenes can be coupled in good yields and with high selectivity with this method. However, the reactions have to be carried out at low temperatures and on avery small scale (0.1 mmol).…”

“…This unique method will also be discussed in detail in our Review on electrochemical methods. [173] Ad ifferent approach was investigated by Waldvogel and co-workers for the selective electrochemical homo-and crosscoupling of phenols,a renes,a nd aniline derivatives.T he distinct solvation properties of the starting materials and reactive intermediates and the unique solvent effects of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) led to high yields and selectivities in the anodic synthesis of coupling products in undivided cells. [107] Solvation by HFIP not only stabilized the reactive intermediates,but also decoupled the nucleophilicity from the oxidation potential owing to the diverse solvation properties of the coupling partners,m aking crosscouplings possible.T he yield and selectivity could be increased in many cases with additives,s uch as water or methanol, that influence the solvation.…”

“…In as econd Review, [173] other conceptual aspects of organic electrosynthesis will be discussed. This thematic structure completes the puzzle of different overviews published over the last few months,a nd surveys the most important achievements of the last decades.…”

Electrochemical and Scalable Dehydrogenative C(sp3)−H Amination via Remote Hydrogen Atom Transfer in Batch and Continuous Flow

“…Or- ganic electrochemistry has attracted increasing attentiono ver the last few years, mainly due to the replacemento fr educing and oxidizing reagents by "traceless" electrons at the cathode and holes at the anode. [12] From ap ractical perspective, organic electrosynthesis can minimize total energyl osses and reduce waste formation,a nd as ar esult,t hese techniques will decreaset he overall costs of industrial synthesis. [13] Because Nradicals can be produced electrochemically,a sh as been demonstrated by Shono and others [14] we aimed to combines uch a strategyw ith as ubsequent1 ,5-HAT( 1,5-hydrogen atom transfer) to circumvent knowno bstacles related to C(sp 3 )ÀHa mination (HLF reaction) and make the developed protocol applicable to large-scale syntheticapplications(Scheme 1).…”