Electrocatalytic Generation of Acyl Radicals and Their Applications

Abstract

In this review, we highlighted the main achievements in the field of electrocatalytic generation of acyl radicals and their applications. These electrochemical strategies were introduced with an emphasis on the substrate scope, reaction limitation and underlying mechanism. The related reactions were categorized according to the pathways of acyl radical generation, including outer-sphere electron transfer (ET), inner-sphere ET, and hydrogen atom transfer (HAT) processes.

Electrochemical synthesis of pyridine carboxamides from pyridine carbohydrazides and amines in an aqueous medium

“…Based on the above results and previous reports, 5,11 we proposed a possible reaction mechanism for the electrochemical amidation of isonicotinohydrazide (Scheme 5). First, the isonicotinohydrazide 1 reacts with the hydroxide ion generated by cathodic reduction to give isonicotinohydrazide anion A , which further reacts with anodically in situ generated molecular iodine to produce the intermediate B .…”

Electrochemical Decarboxylative Minisci-Type Acylation of Quinoxalines under Catalyst- and External-Oxidant-Free Conditions

“…Mechanistically, the Minisci-type acylation includes three key processes: acyl radical generation, radical addition of acyl radicals to N-heterocycles, and formal hydrogen atom loss. While the generation of acyl radical can be driven by direct electro-decarboxylation, 10 the use of a proper activator to accelerate the radical addition step may realize the catalyst-free Minisci-type acylations. Previous reports showed that acidic additive could lower N-heterocycle's LUMO energy, thus favoring the following radical addition.…”

“…When nickel cathode was replaced by Sn plate, Ni foam or graphite, the yield of 3aa decreased dramatically (entries 7-9). Replacing graphite anode with Pt plate or carbon felt led to 37% and 49% yield, respectively (entries 10,11). Changing the solvent from CH 3 CN to DMA or DMF only gave trace amount of desired product 3aa (entries 12, 13).…”

Recent advances in three-component radical acylative difunctionalization of unsaturated carbon–carbon bonds

“…The acyl radical is considered to be a transient nucleophilic σ-radical. 8 Since the pioneering work of Kharasch in 1949, 9 significant progress has been achieved in the acyl radical addition-initiated [10][11][12][13][14] three-component difunctionalization of olefins to provide the β-acylation product. More recently, the use of transition metals (TM) in radical acylation has brought about a new Dawn for the…”