Rhodaelectro-Catalyzed C–H and C–C Activation

Abstract

Rhodium(III) catalysis has set the stage for a plethora of oxidative C-H functionalizations over the last decade, which have predominantly employed stoichiometric amounts of toxic and expensive metal oxidants, such as silver(I) salts. In the meantime, electrosynthesis has emerged as an increasingly viable alternative for expensive and toxic oxidants. Recently, significant momentum has been achieved with the merger of electrocatalysis with organometallic C-H activation. However, user-friendly and robust rhodaelectro-catalysis has until very recently proven elusive for oxidative C-H activations. This minireview highlights the current knowledge and recent advances of electrooxidation in rhodium-catalyzed C-H or C-C activations, with a topical focus on contributions from the Ackermann group through July 2020.

Organic Electrochemistry: Molecular Syntheses with Potential

“…The robust rhodaelectrocatalytic C–H activation 91 allowed electrochemical flow techniques 92 to establish challenging flow-rhodaelectro-catalyzed C–H/N–H alkyne annulations with imidates 52 ( Scheme 11 ). 93 Using cyclic voltammetry and further detailed mechanistic studies by experiment provided novel insights for the rhodaelectrocatalytic manifold.…”

Electro-oxidative Intermolecular Allylic C(sp3)–H Aminations

“…Electrosynthesis has emerged as an increasingly powerful tool for molecular synthesis. − Particularly, the merger of electrochemistry with organometallic catalysis has set the stage for significant advances in C­(sp 2 )–H activation. − In contrast, electro-catalyzed C­(sp 3 )–H activation continues to be scarce. − In this context, Mei and co-workers described the palladium-catalyzed oxygenation of C­(sp 3 )–H bonds using an oxime moiety as the directing group . Recently, progress on electrochemical oxidative C­(sp 3 )–H bond functionalizations under transition-metal-free conditions has been noted.…”

Palladium-catalyzed remote para-C–H activation of arenes assisted by a recyclable pyridine-based template

“…The DG strategy has enabled the development of a large number of ortho -C–H and some meta -C–H transformations of arenes. 1,2 In contrast, although quite a few para -C–H transformations of arenes have been disclosed by making use of arene's electronic and steric biases, 3,4 the para -C–H transformation beyond the control of such biases remains a daunting challenge and is still significantly restricted to a few scaffolds. In this endeavor, Nakao and co-workers reported a breakthrough in para -C–H alkylation and borylation of arenes by cooperative nickel/aluminum and iridium/aluminum catalysis ( Scheme 1a , left).…”

“…However, 2,6-disubstitution of the substrate is unavoidable for this method to achieve the desired selectivity, making it not a general solution. Due to the aforementioned limitations and the good performance of pyridine-based DGs in promoting ortho - 1 and meta -C–H activations, 2 d ,12 the development of a versatile method for para -C–H activation of arenes by taking the advantage of the directing ability of pyridines is highly desirable.…”