Cs2CO3-promoted carboxylation of N-tosylhydrazones with carbon dioxide toward α-arylacrylic acids

Visible Light Photoredox-Catalyzed Formyl/Carboxylation of Activated Alkenes with Glyoxylic Acid Acetals and CO2

A photoredox-catalyzed sequential α-formyl/carboxylation of alkenes with glyoxylic acid acetals and CO2 has been developed to afford a range of masked γ-formyl esters in good yields, which could be readily transformed into diverse compounds, such as γ-formyl ester, hemiacetal, and 1,4-diol. This reaction features mild conditions, readily available starting materials, and operational simplicity.

Visible-Light Photoredox-Catalyzed Intermolecular α-Aminomethyl/Carboxylative Dearomatization of Indoles with CO2 and α-Aminoalkyl Radical Precursors

Disclosed here is a visible-light photoredox-catalyzed intermolecular sequential α-aminomethyl/carboxylative dearomatization of indoles with CO2 and α-aminoalkyl radical precursors, affording a series of functionalized indoline-3-carboxylic acids and lactams in good yields with high regioselectivity. This multicomponent reaction provides a green and facile method for the synthesis of diverse functionalized indolines by using CO2 as the carboxylic and carbonyl source.

Base-mediated carboxylation of C-nucleophiles with CO2

Carbon dioxide (CO2) is an available, abundant, and renewable C1 resource, which could be converted into value-added chemicals. Due to its inherent thermodynamic stability and kinetic inertness, it is difficult to realize its efficient utilization. Nevertheless, many elegant strategies for the utilization of CO2 have been developed using Lewis bases, frustrated Lewis pairs, hydroxyl-containing compounds, amino-group-containing compounds or transition metal catalysis. Among them, base-mediated carboxylation of C-nucleophiles is an environmentally friendly strategy for CO2 conversion, which is operationally simple, using low-toxicity bases and economical available promoters, without the use of complex ligands or cocatalysts. This review summarizes related work on the base-mediated carboxylation of C-nucleophiles with CO2, based on the effects of nucleophiles, promoters, additives, and solvents. The types of pronucleophile are categorized as follows: hydrocarbon with C(sp3)-H, C(sp2)-H or C(sp)-H bonds, organosilanes, organotin, organoboron, and N-tosylhydrazones. Typical mechanisms and applications of these carboxylation reactions are also depicted. Moreover, mechanistic comprehension of CO2 activation and conversion at a molecular level aims to further expand the repertoire of carboxylation transformations mediated by bases.

Base-Promoted 5-exo-dig Cyclization of o-Alkynylamides or 2-En-4-ynamides with CO2 toward Fully Substituted Acrylates

A base-promoted sequential cyclization and carboxylation of o-alkynylamides or 2-en-4-ynamides with CO₂ has been achieved with high efficiency, stereoselectivity, and regioselectivity. This approach begins with 5-exo-dig cyclization followed by trapping the resulting vinyl anion with CO₂ and MeI, which provides a convenient access to diverse cyclic and fully substituted acrylates with CO₂ as the carboxylic source.

Visible-Light Photoredox-Catalyzed Dicarbofunctionalization of Styrenes with Oxime Esters and CO2: Multicomponent Reactions toward Cyanocarboxylic Acids and γ-Keto Acids

A photoredox-catalyzed dicarbofunctionalization of styrenes with oxime esters and CO₂ has been achieved. Notably, a series of four-, five-, or six-membered cyclic ketone oximes worked well to furnish a wide range of ε-, ζ-, and η-cyanocarboxylic acids in good yields. Furthermore, a series of γ-keto acids also could be obtained by employing acyclic ketone oxime esters as the carbonyl radical precursor. It provides convergent access to diverse biologically important cyanocarboxylic and γ-keto acids.

Photoredox-Catalyzed α-Aminomethyl Carboxylation of Styrenes with Sodium Glycinates: Synthesis of γ-Amino Acids and γ-Lactams

A visible-light photoredox-catalyzed reductive α-aminomethyl carboxylation of styrenes with sodium glycinates and CO₂ has been developed to synthesize a series of α,α-disubstituted γ-amino acids and γ-lactams with high efficiency and regioselectivity. Notably, CO₂ released from the decarboxylation step can be reused for the subsequent carboxylation. Distinct from the previous reactions with the same type of substrates leading to simple decarboxylation and olefin hydroalkylation, this process involves additional CO₂ sequestration, thus leading to olefin α-aminomethyl carboxylation. These findings not only provide new access to α,α-disubstituted γ-amino acids and γ-lactams but also serve as a proof of concept for CO₂ reutilization in decarboxylation reactions.

Palladium/copper-catalyzed multicomponent reactions of propargylic amides, halohydrocarbons and CO2 toward functionalized oxazolidine-2,4-diones

A palladium/copper-catalyzed oxy-carbonation of propargylic amides by halohydrocarbons and CO2 has been developed toward functionalized oxazolidine-2,4-diones. This multi-component reaction (MCR) was triggered by the oxidative addition of RX to Pd(0), followed by the sequential carboxylation of amide and trans-oxopalladation of an electron-deficient triple bond by RPdX species. Finally, the reductive elimination afforded products possessing tetra-substituted vinyl motifs and Pd(0). This protocol features simultaneous formation of three bonds, representing an efficient method for incorporation of CO2 into value-added heterocycles.

Ruthenium-catalyzed umpolung carboxylation of hydrazones with CO2

The first ruthenium-catalyzed umpolung carboxylation of hydrazones with CO₂ to generate important aryl acetic acids is reported.

The first ruthenium-catalyzed umpolung carboxylation of hydrazones with CO₂ to generate important aryl acetic acids is reported. Besides aldehyde hydrazones, a variety of ketone hydrazones, which have not been successfully applied in previous umpolung reactions with other reactive electrophiles, also show high reactivity and selectivity under mild conditions. Moreover, this operationally simple protocol features good functional group tolerance, is readily scalable, and offers easy derivation of important structures, including bioactive felbinac and adiphenine. Computational studies reveal that this umpolung reaction proceeds through the generation of a Ru-nitrenoid followed by concerted [4 + 2] cycloaddition with CO₂.

One-Step Synthesis of Sulfonamides from N-Tosylhydrazones

The first described reaction between N-tosylhydrazone and SO2 is reported to provide alkyl sulfonamides in the presence of various amines. In this procedurally simple method, hydrazones of both unsaturated aldehydes and ketones proceed in moderate to excellent yields. Primary and secondary aliphatic amines are accommodated in this reaction, which provides a novel route to sulfonamides.