Recent Advances in Oxidative R¹-H/R²-H Cross-Coupling with Hydrogen Evolution via Photo-/Electrochemistry

Abstract

Photo-/electrochemical catalyzed oxidative R 1 -H/R 2 -H cross-coupling with hydrogen evolution has become an increasingly important issue for molecular synthesis. The dream of construction of C−C/C−X bonds from readily available C− H/X−H with release of H 2 can be facilely achieved without external chemical oxidants, providing a greener model for chemical bond formation. Given the great influence of these reactions in organic chemistry, we give a summary of the state of the art in oxidative R 1 -H/R 2 -H cross-coupling with hydrogen evolution via photo/electrochemistry, and we hope this review will stimulate the development of a greener synthetic strategy in the near future.

Photoinduced site-selective alkenylation of alkanes and aldehydes with aryl alkenes

“…The direct alkenylation of aldehydes represents a highly attractive and sustainable strategy for the synthesis of this important family of compounds. We were excited to find that various primary and secondary aldehydes were effective substrates under the optimal alkenylation conditions, providing α,β-unsaturated ketones in decent yields with exclusive E selectivity (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43). Notably, excellent site selectivity was observed for aldehyde C-H bonds, while other activated C-H bonds, such as benzylic (34), allylic (38), propargylic (39) and α-heteroatom C-H bonds (42 and 43), were not functionalized.…”

“…In this context, we were inspired by direct hydrogen atom transfer (HAT) photocatalysts that could achieve the straightforward activation of C-H bonds 33 decatungstate anion ([W 10 O 32 ] 4− ), a polyoxometalate photocatalyst that has been broadly applied in various functionalizations of alkanes and aldehydes [34][35][36][37][38][39] . On the other hand, photocatalytic dehydrogenative cross-coupling reactions with concomitant hydrogen evolution have recently been developed through cooperative photoredox and cobaloxime catalysis, as pioneered by the Wu and Lei groups [40][41][42][43][44] . Inspired by these studies, we proposed that the combination of decatungstate anion and a cobaloxime catalyst could enable the direct activation and alkenylation of alkanes and aldehydes using alkenes as the feedstocks.…”

Oxidative Dearomative Cross-Dehydrogenative Coupling of Indoles with Diverse C-H Nucleophiles: Efficient Approach to 2,2-Disubstituted Indolin-3-ones

“…Direct C-H functionalization has emerged as an elegant approach to the construction of C-C bonds [1][2][3][4][5][6][7]. Particularly, oxidative cross-dehydrogenative coupling (CDC) from two readily available C-H bonds features the advantage of high step-and atom-economy, as it does not require pre-functionalized substrates [8][9][10][11][12].…”

Photoredox Catalysis of Aromatic β‐Ketoesters for in Situ Production of Transient and Persistent Radicals for Organic Transformation

“…[2] Through either reductive quenching by an electron donor (reductant) or oxidative quenching by an electron acceptor (oxidant), the generated reactive radical intermediates exhibit rich synthetic reactivity for subsequent reactions. [3] Over the past decade, these photocatalytic designs have spurred tremendous research interest and there have been numerous advances in an array of photoredox catalytic reactions, for example, crosscoupling reactions, [4] a-amino/oxy/carbonyl C(sp 3 )ÀH bond functionalization, [5] cycloadditions, [6] reductive umpolung of carbonyl derivatives, [7] and dehalogenation reactions. [8] In these reactions, however, stoichiometric external oxidant or reductant is often required for subsequent oxidative or reductive reactions.…”