Olefination of carbonyls with alkenes enabled by electrophotocatalytic generation of distonic radical cations

Abstract

The conversion of carbonyls to olefins is a transformation of great importance for complex molecule synthesis. Standard methods use stoichiometric reagents that have poor atom economy and require strongly basic conditions, which limit their functional group compatibility. An ideal solution would be to catalytically olefinate carbonyls under nonbasic conditions using simple and widely available alkenes, yet no such broadly applicable reaction is known. Here, we demonstrate a tandem electrochemical/electrophotocatalytic reaction to olefinate aldehydes and ketones with a broad range of unactivated alkenes. This method involves the oxidation-induced denitrogenation of cyclic diazenes to form 1,3-distonic radical cations that rearrange to yield the olefin products. This olefination reaction is enabled by an electrophotocatalyst that inhibits back-electron transfer to the radical cation intermediate, thus allowing for the selective formation of olefin products. The method is compatible with a wide range of aldehydes, ketones, and alkene partners.

Shining Fresh Light on Complex Photoredox Mechanisms through Isolation of Intermediate Radical Anions

“…An excellent example of the confusion that can surround PRC mechanisms is found in the related areas of “conPET” (consecutive photoinduced electron transfer) and “electrochemically-mediated PRC” (e-PRC). , These are adaptations of the ‘standard’ PRC mechanism that have both attracted particularly intense interest in recent years as they allow the catalysts employed to generate extremely reducing (or oxidizing) potentials that exceed those normally accessible in visible light PRC (though there is no strict limit, potentials beyond ca. ±2 V vs SCE are commonly considered difficult to achieve for standard PRC) .…”

Olefination of aldehydes with alpha-halo redox-active esters

“…11 The development of mild carbonyl olefinations from simple precursors ideally in one step remains an active and important research topic. 12–25 Herein, we disclose a reductive olefination from aldehydes and readily accessible α-bromo carboxylic acid derivatives under simple and practical conditions (Fig. 1C).…”

Investigating the Potency of a Phenalenyl-Based Photocatalyst under the Photoelectrochemical Condition for Intramolecular C–S Bond Formation

“…Just after this discovery, Stahl et al implemented the halide ion as a redox mediator in PEC to enable the formation of the challenging C–N bond. Lambert et al have elucidated the anodic oxidation of the trisaminocyclopropenium ion ( TAC + ) to yield the active photocatalyst TAC 2+ , which, when exposed to light, is involved in numerous important photoelectrochemical reactions. When 9,10-dicyanoanthracene ( DCA ) was first introduced as a catalyst for photoelectrochemical reactions, the same group demonstrated the functionalization of the C–X (X = halogen) bond by employing DCA .…”