An Electrochemical Beckmann Rearrangement: Traditional Reaction via Modern Radical Mechanism

Abstract

Electrosynthesis as a potential means of introducing heteroatoms into the carbon framework is rarely studied. Herein, the electrochemical Beckmann rearrangement, i. e. the direct electrolysis of ketoximes to amides, is presented for the first time. Using a constant current as the driving force, the reaction can be easily carried out under neutral conditions at room temperature. Based on a series of mechanistic studies, a novel radical Beckmann rearrangement mechanism is proposed. This electrochemical Beckmann rearrangement does not follow the trans-migration rule of the classical Beckmann rearrangement.

Mass spectrometric detection of fleeting neutral intermediates generated in electrochemical reactions

“…6,7 Accurate identification of such intermediates is essential for deriving the reaction mechanisms and further developing efficient reaction systems or novel materials. The most commonly used characterization techniques include density functional theory (DFT) calculation, 8,9 cyclic voltammetry (CV), 10,11 electron paramagnetic resonance spectroscopy (EPR) [12][13][14] and spin trapping, 2 however, these methods are either off-line or unable to directly detect the neutral intermediates.…”

Contemporary Approaches for Amide Bond Formation

“…[230] Recent progress in the Beckmann rearrangement has also revolved around alternative energy sources. In this context, Guan and He showcased the potential of electrochemical induction (Figure 51c), [231] and Porcheddu and co-workers demonstrated the application of mechanical forces to facilitate the rearrangement. [232] Both approaches displayed a remarkable substrate scope.…”

The Mechanochemical Beckmann Rearrangement over Solid Acids: From the Ball Mill to the Extruder

“…The oximes 1 c–g were synthesized from the corresponding ketones according to a literature procedure (cf. Supporting Information, chapter 3.3) [8] …”

“…The underlying BKR as it is done in the industry is conducted in the liquid phase and is acid-catalyzed by an excess of hazardous oleum at elevated temperatures (Scheme 1, a). A wide range of other Brønsted and Lewis acids have been investigated as catalysts, in the liquid phase, while also a plethora of other methods such as organocatalytic [4] , photocatalytic [5] , gas-liquid [6] , or radical [7,8] reaction pathways are described. Of these more exotic variants, however, none has achieved industrial relevance.…”