Site‐Selective Electrochemical C−H Carboxylation of Arenes with CO₂

Abstract

Herein, a direct, metal-free, and site-selective electrochemical CÀ H carboxylation of arenes by reductive activation using CO 2 as the economic and abundant carboxylic source was reported. The electrocarboxylation was carried out in an operationally simple manner with high chemo-and regioselectivity, setting the stage for the challenging site-selective CÀ H carboxylation of unactivated (hetero)arenes. The robust nature of the electrochemical strategy was reflected by a broad scope of substrates with excellent atom economy and unique selectivity. Notably, the direct and selective CÀ H carboxylation of various challenging arenes worked well in this approach, including electron-deficient naphthalenes, pyridines, simple phenyl derivatives, and substituted quinolines. The method benefits from being externally catalyst-free, metal-free and base-free, which makes it extremely attractive for potential applications.

Selective Electroreductive Hydroboration of Olefins with B2pin2

“…Within our continuous interests in sustainable electrochemical transformation, we have now developed a selective protocol for hydroboration of olefins with B 2 pin 2 via an electroreductive approach (Scheme ). Notable features of this strategy include the following: (a) transition metal-free or organo-catalyst-free process, (b) high chemo- and regioselectivities, giving anti-Markovnikov-type hydroboration products, (c) using electrons as an environmentally friendly reductant, and (d) achieving deuterium borylation products with excellent D-incorporation using CD 3 CN.…”

Room Temperature Construction of Vicinal Amino Alcohols via Electroreductive Cross-Coupling of N-Heteroarenes and Carbonyls

“…However, such a strategy remains a yet unresolved goal on account of the challenge in merging the reduction of two reducible reactants and the coupling process into an ordered sequence. It is noteworthy that because of the high tunability of the potential, current, electrode, and electrolyte of electrochemistry, electroreduction has emerged as an appealing tool to create various chemical bonds. − As such, we anticipated that the electroreduction would offer a solution for the above synthetic purpose (Scheme c) by addressing the following issues: (1) selective reduction of two reducible reactants is required to avoids the generation of undesired cyclic amine and alcohol byproducts; (2) the radicals arising from carbonyls are stable enough to trap the N -heteroarenes; and (3) protonation is a key step to incorporate an H atom into the products because it is essential to suppress the thermodynamically favorable hydrogen evolution reaction (Δ G HER = −20 to −60 kcal/mol) on the cathode…”

“…Here, we hypothesized that the Lewis acid generated from anodic oxidation can activate the N -heteroarenes and lower the overpotential during the N -heteroaryl reduction. Thus, we initiated our studies by using an undivided cell containing zinc anode and graphite plate cathode. The sacrificial anode was anticipated to facilitate the cathodic half-cell reaction and serve as the reductant and the source of Lewis acid by leeching Zn 2+ into the reaction solution.…”

Revisiting the Electrochemical Carboxylation of Naphthalene with CO2: Selective Monocarboxylation of 2-Substituted Naphthalenes

“…3 Among the reported electrochemical carboxylations with CO 2 , modifications of unsaturated bonds via C−C bond formation with CO 2 have been reported, 4 albeit that the carboxylation of stable and planar aromatic 5 and heteroaromatic 6 compounds via a dearomative process to afford carboxylic acids has not yet been investigated systematically. 7 In this context, Wearring reported the first naphthalene carboxylation with CO 2 in 1959, 5a in which a dearomative dicarboxylation selectively afforded 1,4-dicarboxylated 1,4-dihydronaphthalene derivatives (Figure 1, eq 1). Subsequently, the same reaction pattern was modified using different electrochemical conditions such as a high pressure of CO 2 (e.g., 4 atm) and different electrodes.…”