The direct β-selective hydrocarboxylation of styrenes under atmospheric pressure of CO2 has been developed using photoredox catalysis in continuous flow. The scope of this methodology was demonstrated with a range of functionalized terminal styrenes, as well as α-substituted and β-substituted styrenes.

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Direct β-Selective Hydrocarboxylation of Styrenes with CO2 Enabled by Continuous Flow Photoredox Catalysis

Carbon dioxide (CO2 ) represents the most abundant and accessible carbon source on Earth. Thus the ability to transform CO2 into valuable commodity chemicals through the construction of C-C bonds is an invaluable strategy. Carboxylic acids and derivatives, the main products obtained by carboxylation of carbon nucleophiles by reaction of CO2 , have wide application in pharmaceuticals and advanced materials. Among the variety of carboxylation methods currently available, the direct carboxylation of C-H bonds with CO2 has attracted much attention owing to advantages from a step- and atom-economical point of view. In particular, the prevalence of (hetero)aromatic carboxylic acids and derivatives among biologically active compounds has led to significant interest in the development of methods for their direct carboxylation from CO2 . Herein, the latest achievements in the area of direct C-H carboxylation of (hetero)aromatic compounds with CO2 will be discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cssc.201701058

C-H Carboxylation of Aromatic Compounds through CO2 Fixation.

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.

C-H Bond Carboxylation with Carbon Dioxide.

The history of silyl cations has all the makings of a drama but with a happy ending. Being considered reactive intermediates impossible to isolate in the condensed phase for decades, their actual c...

Silylium Ions: From Elusive Reactive Intermediates to Potent Catalysts.

A photoinduced carboxylation of alkyl halides with CO2 at remote sp(3) C-H sites enabled by the merger of photoredox and Ni catalysis is described. This protocol features a predictable reactivity and site selectivity that can be modulated by the ligand backbone. Preliminary studies reinforce a rationale based on a dynamic displacement of the catalyst throughout the alkyl side chain.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201902095

Site-Selective, Remote sp3 C-H Carboxylation Enabled by the Merger of Photoredox and Nickel Catalysis.

Me2AlCl-mediated carboxylation, ethoxycarbonylation, and carbamoylation of indoles

The Friedel–Crafts-type carboxylation of arenes has been achieved by activating CO2 with silylium borates. The reaction exhibits broader substrate applicability than does our previously reported Al...

Electrophilic Aromatic Substitution of Arenes with CO2 Mediated by R3SiB(C6F5)4

Lewis acid-mediated β-selective hydrocarboxylation of α,α-diaryl- and α-arylalkenes with R3SiH and CO2

Indene-2-carboxylic acids are prepared from allenylbenzenes and CO2 by an AlBr3-mediated tandem reaction consisting of intramolecular Friedel–Crafts alkylation of allenylbenzenes and subsequent car...

AlBr3-Mediated Tandem Cyclization–Carboxylation of Allenylbenzenes with CO2 in the Presence of Pyridines

The Friedel—Crafts-type carboxylation of arenes is achieved by activation of carbon dioxide with silylium borates.

Masafumi Chiba

Papers

Me2AlCl-mediated carboxylation, ethoxycarbonylation, and carbamoylation of indoles

Electrophilic Aromatic Substitution of Arenes with CO2 Mediated by R3SiB(C6F5)4

Lewis acid-mediated β-selective hydrocarboxylation of α,α-diaryl- and α-arylalkenes with R3SiH and CO2

AlBr3-Mediated Tandem Cyclization–Carboxylation of Allenylbenzenes with CO2 in the Presence of Pyridines

Electrophilic Aromatic Substitution of Arenes with CO2 Mediated by R3SiB(C6F5)4.