Ligand-enabled site-selectivity in a versatile rhodium(ii)-catalysed aryl C–H carboxylation with CO2

Reductive Coupling of Carbon Dioxide and an Aldehyde Mediated by a Copper(I) Complex toward the Synthesis of α-Hydroxycarboxylic Acids

Copper-mediated reductive coupling between CO₂ and an aldehyde to form α-hydroxycarboxylic acid was achieved using silylborane as a reductant. CO₂ cleanly inserted into a copper-carbon bond that was formed by the reaction between a silylcopper-NHC complex and an aldehyde. A series of reactions that regenerate the silylcopper complex were developed for the synthesis of an α-hydroxycarboxylic acid. After repeating each step iteratively for two cycles, 0.62 equiv of α-hydroxycarboxylic acid based on the copper complex was obtained.

CO2 = CO + [O]: recent advances in carbonylation of C–H bonds with CO2

Carbon dioxide (CO₂) is an ideal one-carbon source owing to its nontoxicity, abundance, availability, and recyclability.

Access to 5H-benzo[a]carbazol-6-ols and benzo[6,7]cyclohepta[1,2-b]indol-6-ols via rhodium-catalyzed C–H activation/carbenoid insertion/aldol-type cyclization

The rhodium-catalyzed mono-ortho C–H activation/carbenoid insertion/aldol-type cyclization of 3-aldehyde-2-phenyl-1H-indoles with diazo compounds has been developed.

Overriding ortho selectivity by template assisted meta-C–H activation of benzophenones

A regioselective meta-C–H activation strategy for benzophenone was successfully developed by overriding the inherent ketone-directed ortho-selectivity.

Photocarboxylation of Benzylic C-H Bonds

The carboxylation of sp³-hybridized C–H bonds with CO₂ is a challenging transformation. Herein, we report a visible-light-mediated carboxylation of benzylic C–H bonds with CO₂ into 2-arylpropionic acids under metal-free conditions. Photo-oxidized triisopropylsilanethiol was used as the hydrogen atom transfer catalyst to afford a benzylic radical that accepts an electron from the reduced form of 2,3,4,6-tetra(9H-carbazol-9-yl)-5-(1-phenylethyl)benzonitrile generated in situ. The resulting benzylic carbanion reacts with CO₂ to generate the corresponding carboxylic acid after protonation. The reaction proceeded without the addition of any sacrificial electron donor, electron acceptor or stoichiometric additives. Moderate to good yields of the desired products were obtained in a broad substrate scope. Several drugs were successfully synthesized using the novel strategy.

Nickel-Catalyzed Carboxylation of Aryl and Heteroaryl Fluorosulfates Using Carbon Dioxide

The development of efficient and practical methods to construct carboxylic acids using CO₂ as a C1 synthon is of great importance. Nickel-catalyzed carboxylation of aryl fluorosulfates and heteroaryl fluorosulfates with CO₂ is described, affording arene carboxylic acids with good to excellent yields under mild conditions. In addition, a one-pot phenol fluorosulfation/carboxylation is developed.

Direct Carboxylation of Electron-Rich Heteroarenes Promoted by LiO-tBu with CsF and [18]Crown-6

We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C-H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species.

C-H Bond Carboxylation with Carbon Dioxide

Carbon dioxide is a nontoxic, renewable, and abundant C₁ source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chemical transformation of CO₂ with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivatives. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp² )-H bonds of (hetero)arenes, vinylic C(sp² )-H bonds, the ipso-C(sp² )-H bonds of the diazo group, aldehyde C(sp² )-H bonds, α-C(sp³ )-H bonds of the carbonyl group, γ-C(sp³ )-H bonds of the carbonyl group, C(sp³ )-H bonds adjacent to nitrogen atoms, C(sp³ )-H bonds of o-alkyl phenyl ketones, allylic C(sp³ )-H bonds, C(sp³ )-H bonds of methane, and C(sp³ )-H bonds of halogenated aliphatic hydrocarbons. In addition, multicomponent reactions, tandem reactions, and key theoretical studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochemical, and light-driven methods are highlighted.

Computational exploration of substrate and ligand effects in nickel-catalyzed C–Si bond carboxylation with CO2

The ring strain of substrates and steric hindrance of NHC ligands are the key factors affecting the reactivity of CO₂ insertion into sila-nickelacycles.

Recent advances in nucleophile-triggered CO2-incorporated cyclization leading to heterocycles

CO₂, as a sustainable, feasible, abundant one-carbon synthon, has been utilized in carboxylative cyclization, carbonylative cyclization, and reductive cyclization.

Pd(ii)/Ag(i)-Cocatalyzed ortho direct arylation of O-phenylcarbamates with pinacol aryl boronates

Ortho direct arylation of O-phenyl carbamates using aryl boronates as coupling partners has been realized for the first time using Pd(OAc)₂ and AgOAc as co-catalyst.

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

Carbon dioxide (CO₂) is one of the most important materials as renewable chemical feedstock. In this review, the Co- and Rh-catalyzed transformation of CO₂ via carbon-carbon bond-forming reactions is summarized. Combinations of metals (cobalt or rhodium), substrates, and reducing agents realize efficient carboxylation reactions using CO₂. The carboxylation of propargyl acetates and alkenyl triflates using cobalt complexes as well as the cobalt-catalyzed reductive carboxylation of α,β-unsaturated nitriles and carboxyamides in the presence of Et₂Zn proceed. A Co complex has been demonstrated to act as an efficient catalyst in the carboxylation of allylic C(sp³)-H bonds. Employing zinc as the reductant, carboxyzincation and the four-component coupling reaction between alkyne, acrylates, CO₂, and zinc occur efficiently. Rh complexes also catalyze the carboxylation of arylboronic esters, C(sp²)-H carboxylation of aromatic compounds, and hydrocarboxylation of styrene derivatives. The Rh-catalyzed [2 + 2 + 2] cycloaddition of diynes and CO₂ proceeds to afford pyrones.

Catalytic Lactonization of Unactivated Aryl C-H Bonds with CO2: Experimental and Computational Investigation

The first catalytic lactonization of unactivated aryl C-H bonds with CO₂ to afford important phthalides is reported. Notably, this method features high selectivity, excellent functional group tolerance, smooth scalability, and facile product diversification. DFT calculations reveal that a novel insertion of two CO₂ into the O-Pd bond of a palladacycle might be the key step, providing great potential and a different perspective for carbonylation with CO₂.