Homogeneous Light-Driven Catalytic Direct Carboxylation with CO 2

Visible-light-driven alkene dicarboxylation with formate and CO2 under mild conditions

Low-cost formate salt was used as the reductant and part of the carboxyl source in a visible-light-driven dicarboxylation of diverse alkenes, including simple styrenes. The highly competing hydrocarboxylation side reaction was successfully overridden. Good yields of products were obtained under mild reaction conditions at ambient temperature and pressure of CO2. The dual role of formate salt may stimulate the discovery of a range of new transformations under mild and friendly conditions.

Carboxylic Acid Salts as Dual-Function Reagents for Carboxylation and Carbon Isotope Labeling

The potassium salts of carboxylic acids are developed as efficient carboxylating agents through CO₂ exchange. We describe these carboxylates as dual-function reagents because they function as a combined source of CO₂ and base/metalating agent. By using the salt of a commercially available carboxylic acid, this protocol overcomes difficulties when using CO₂ gas or organometallic reagents, such as pressurized containers or strictly inert conditions. The reaction proceeds under mild conditions, does not require transition metals or other additives, and shows broad substrate scope. Through the preparation of several biologically important molecules, we show how this strategy provides an opportunity for isotope labeling with low equivalents of labeled CO₂ .

Nickel-Catalyzed Enantioconvergent Carboxylation Enabled by a Chiral 2,2'-Bipyridine Ligand

In contrast to previous approaches to chiral α-aryl carboxylic acids that based on reactions using hazardous gases, pressurized setup and mostly noble metal catalysts, in this work, a nickel-catalyzed general, efficient and highly enantioselective carboxylation reaction of racemic benzylic (pseudo)halides under mild conditions using atmospheric CO₂ has been developed. A unique chiral 2,2'-bipyridine ligand named Me-SBpy featuring compact polycyclic skeleton enabled both high reactivity and stereoselectivity. The utility of this method has been demonstrated by synthesis of various chiral α-aryl carboxylic acids (30 examples, up to 95 % yield and 99 : 1 er), including profen family anti-inflammatory drugs and transformations using the acids as key intermediates. Based on mechanistic experimental results, a plausible catalytic cycle involving Ni-complex/radical equilibrium and Lewis acid-assisted CO₂ activation has been proposed.

Dendritic fibrous nanosilica-supported dendritic IL/Ru(ii) as photocatalysts for the dicarbofunctionalization of styrenes with carbon dioxide and amines

The effectual utilization of heterogeneous catalysts from nano sources through chemical moderation for the α-aminomethylcarboxylation of alkenes with carbon dioxide and amines is an attractive area to study. Dendritic fibrous nanosilica (DFNS) is a cost-effective, resistant, plenteous, and reproducible source with dandelion-like fibrous anatomy. The present paper is a report on an easy method to provide a family of new DFNS-supported dendritic imidazolium IL/Ru(ii) heterogeneous catalysts DFNS/IL/Ru (1-3) with high ionic density from DFNS. A positive dendritic effect was perceived in the chemical stabilization performance of CO2. DFNS/IL/Ru(ii) was appropriately identified by UV-vis spectroscopy, XPS, SEM, TEM, FT-IR spectroscopy, and TGA. It was discovered that DFNS/IL/Ru(ii) has high catalytic activity for the synthesis of quinoline-2-one through the annulation of ortho-heteroaryl anilines and CO2. DFNS/IL/Ru (3) could be reutilized ten continuous times with no notable reduction in the catalytic activity. Notably, the coveted quinoline-2-one was prepared on a multi-gram scale by deploying DFNS/IL/Ru (3) as a green heterogeneous catalyst. Owing to the attendance of the zwitterionic liquid functional groups on the exterior layer of the bio-based DFNS/IL/Ru (3) catalyst, DFNS/IL/Ru (3) expressed the highest catalytic activity. This approach provides highly functional γ-amino acids in proper yields with great selective power. This paper announces the first nanocatalyst for this transformation, comprising the DFNS-supported Ru N-heterocyclic carbine complex.

Functional Group-Directed Photochemical Reactions of Aromatic Alcohols, Amines, and Thiols Triggered by Excited-State Hydrogen Detachment: Additive-free Oligomerization, Disulfidation, and C(sp2)-H Carboxylation with CO2

Exploring new types of photochemical reactions is of great interest in the field of synthetic chemistry. Although excited-state hydrogen detachment (ESHD) represents a promising prospective template for additive-free photochemical reactions, applications of ESHD in a synthetic context remains scarce. Herein, we demonstrate the expansion of this photochemical reaction toward oligomerization, disulfidation, and regioselective C(sp²)-H carboxylation of aromatic alcohols, thiols, and amines. In the absence of any radical initiators in tetrahydrofuran upon irradiation with UV light (λ = 280 or 300 nm) under an atmosphere of N₂ or CO₂, thiols and catechol afforded disulfides and oligomers, respectively, as main products. Especially, the photochemical disulfidation proceeded highly selectively with the NMR and quantum yields of up to 69 and 0.46%, respectively. In stark contrast, the photolysis of phenylenediamines and aminophenols results in photocarboxylation in the presence of CO₂ (1 atm). p-Aminophenol was quantitatively carboxylated by photolysis for 17 h with a quantum yield of 0.45%. Furthermore, the photocarboxylation of phenylenediamines and aminophenols proceeds in a highly selective fashion on the aromatic C(sp²)-H bond next to a functional group, which is directed by the site-selective ESHD of the functional groups for the formation of aminyl and hydroxyl radicals.

Light-Mediated Carboxylation Using Carbon Dioxide

Carbon dioxide is a green and sustainable one-carbon source, which could be utilized in the production of various fine chemicals. In recent studies, the light-mediated carboxylation employing CO₂ has received considerable attention. The photocarboxylation of substrates with CO₂ to build novel C-C bonds is introduced in this Minireview. The article is arranged based on the light-driven reactive intermediates, including CO₂ radical anion, substrate radical anions, carbanions, and M-C species. Most of the cases are under the topic of photoredox catalysis, with single electron transfer as the main driving force. Some non-catalytic examples are also discussed to provide more mechanistic insights.

Visible-Light Photoredox-Catalyzed Ring-Opening Carboxylation of Cyclic Oxime Esters with CO2

The carboxylation of cyclic oxime esters with carbon dioxide via visible-light photoredox catalysis is demonstrated for the first time. A variety of cyclic oxime esters undergo ring-opening C-C bond cleavage and carboxylation to give cyanoalkyl-containing carboxylic acids in moderate to good yields. Moreover, this methodology features mild reaction conditions (room temperature, 1 atm), wide substrate scope, good functional group tolerance as well as facile derivations of products. Mechanistic studies indicate that the benzylic radicals and anions might be the key intermediates.

Utilization of CO2 Feedstock for Organic Synthesis by Visible-Light Photoredox Catalysis

CO₂ is a highly abundant, green, and sustainable carbon feedstock. Despite its kinetic inertness and thermodynamic stability, the development of various catalytic techniques has enabled the conversion of CO₂ to value-added products such as carboxylic acids, amino acids, and heterocyclic compounds, where visible-light photocatalysis has emerged to be an efficient promoter of these processes. This Minireview covers the progress in the areas of CO₂ incorporation onto organic matters based on the combined venture of renewable resources of CO₂ and light energy with significant emphasis on the last three years' developments.

Organic synthesis of fixed CO2 using nitrogen as a nucleophilic center

In this review, recent progress in the application of CO2 as an electrophilic reagent and nitrogen as a nucleophilic center under different catalytic conditions in organic synthesis is summarized. The used catalytic methods in the reactions of CO2 and nitrogen are classified as metal catalysis, metal-free catalysis, photocatalysis and electrocatalysis. Various catalytic conditions have been used to solve the problems of thermodynamic properties and stability of CO2. The transformation mechanisms of these reactions are discussed.

Visible-Light Photoredox-Catalyzed Remote Difunctionalizing Carboxylation of Unactivated Alkenes with CO2

Remote difunctionalization of unactivated alkenes is challenging but a highly attractive tactic to install two functional groups across long distances. Reported herein is the first remote difunctionalization of alkenes with CO₂ . This visible-light photoredox catalysis strategy provides a facile method to synthesize a series of carboxylic acids bearing valuable fluorine- or phosphorus-containing functional groups. Moreover, this versatile protocol shows mild reaction conditions, broad substrate scope, and good functional-group tolerance. Based on DFT calculations, a radical adds to an unactivated alkene to smoothly form a new carbon radical, followed by a 1,5-hydrogen atom-transfer process, the rate-limiting step, generating a more stable benzylic radical. The reduction of the benzylic radicals by an Ir^II species generates the corresponding benzylic carbanions as the key intermediates, which further undergo nucleophilic attack with CO₂ to generate carboxylates.

Electroreductive Cobalt-Catalyzed Carboxylation: Cross-Electrophile Electrocoupling with Atmospheric CO2

The chemical use of CO2 as an inexpensive, nontoxic C1 synthon is of utmost topical interest in the context of carbon capture and utilization (CCU). We present the merger of cobalt catalysis and electrochemical synthesis for mild catalytic carboxylations of allylic chlorides with CO2 . Styrylacetic acid derivatives were obtained with moderate to good yields and good functional group tolerance. The thus-obtained products are useful as versatile synthons of γ-arylbutyrolactones. Cyclic voltammetry and in operando kinetic analysis were performed to provide mechanistic insights into the electrocatalytic carboxylation with CO2 .

Reductive dearomative arylcarboxylation of indoles with CO2 via visible-light photoredox catalysis

Catalytic reductive coupling of two electrophiles and one unsaturated bond represents an economic and efficient way to construct complex skeletons, which is dominated by transition-metal catalysis via two electron transfer. Herein, we report a strategy of visible-light photoredox-catalyzed successive single electron transfer, realizing dearomative arylcarboxylation of indoles with CO₂. This strategy avoids common side reactions in transition-metal catalysis, including ipso-carboxylation of aryl halides and β-hydride elimination. This visible-light photoredox catalysis shows high chemoselectivity, low loading of photocatalyst, mild reaction conditions (room temperature, 1 atm) and good functional group tolerance, providing great potential for the synthesis of valuable but difficultly accessible indoline-3-carboxylic acids. Mechanistic studies indicate that the benzylic radicals and anions might be generated as the key intermediates, thus providing a direction for reductive couplings with other electrophiles, including D₂O and aldehyde.

Catalytic reductive coupling of two electrophiles and one C = C bond is usually performed by two electron transfer metal catalysis. Herein, the authors show a visible light photoredox-catalyzed successive single electron transfer leading to dearomative arylcarboxylation of indoles with CO₂ and generating indoline-3-carboxylic acids.

Transition metal-free phosphonocarboxylation of alkenes with carbon dioxide via visible-light photoredox catalysis

Catalytic difunctionalization of alkenes has been an ideal strategy to generate structurally complex molecules with diverse substitution patterns. Although both phosphonyl and carboxyl groups are valuable functional groups, the simultaneous incorporation of them via catalytic difunctionalization of alkenes, ideally from abundant, inexpensive and easy-to-handle raw materials, has not been realized. Herein, we report the phosphonocarboxylation of alkenes with CO2 via visible-light photoredox catalysis. This strategy is sustainable, general and practical, providing facile access to important β-phosphono carboxylic acids, including structurally complex unnatural α-amino acids. Diverse alkenes, including enamides, styrenes, enolsilanes and acrylates, undergo such reactions efficiently under mild reaction conditions. Moreover, this method represents a rare example of redox-neutral difunctionalization of alkenes with H-P(O) compounds, including diaryl- and dialkyl- phosphine oxides and phosphites. Importantly, these transition-metal-free reactions also feature low catalyst loading, high regio- and chemo-selectivities, good functional group tolerance, easy scalability and potential for product derivatization.

Selective C-F bond carboxylation of gem-difluoroalkenes with CO2 by photoredox/palladium dual catalysis

The catalytic C-F bond carboxylation of organofluorines with CO2 gas remains a challenging problem in synthetic chemistry. Here, we describe a selective defluorinative carboxylation of gem-difluoroalkenes through photoredox/palladium dual catalysis. The C-F bond activation is enabled by single electron reduction through photoredox catalysis to generate a fluorovinyl radical, which subsequently participates in an unprecedented palladium-catalyzed carboxylation. This novel C-F functionalization proved applicable to a wide range of substituted gem-difluoroalkenes, providing a rapid access to valuable α-fluoroacrylic acids.

Phosphine-catalyzed fixation of CO2 with γ-hydroxyl alkynone under ambient temperature and pressure: kinetic resolution and further conversion

Phosphine-catalyzed fixation of CO₂ with γ-hydroxyl alkynone under ambient temperature and pressure was achieved and the first example of chiral phosphine catalyzed kinetic resolution of propargyl alcohols via carbon dioxide fixation was demonstrated.

Tandem one-pot CO2 reduction by PMHS and silyloxycarbonylation of aryl/vinyl halides to access carboxylic acids

The present study discloses the synthesis of aryl/vinyl carboxylic acids from Csp2-bound halides (Cl, Br, I) in a carbonylative path by using silyl formate (from CO2 and hydrosilane) as an instant CO-surrogate. Hydrosilane provides hydride for reduction and its oxidation product silanol serves as a coupling partner. Mono-, di-, and tri-carboxylic acids were obtained from the corresponding aryl/vinyl halides.

Selective and Catalytic Hydrocarboxylation of Enamides and Imines with CO2 to Generate α,α-Disubstituted α-Amino Acids

The first catalytic hydrocarboxylation of enamides and imines with CO₂ to generate valuable α,α-disubstituted α-amino acids is reported. Notably, excellent chemo- and regio-selectivity are achieved, significantly different from previous reports on β-carboxylation of enamides, homocoupling or reduction of imines. Moreover, this transition-metal-free procedure exhibits low loading of an inexpensive catalyst, easily available substrates, mild reaction conditions, high efficiency, facile scalability and easy product derivatization, providing great potential for application in organic synthesis, pharmaceutical chemistry, and biochemistry.

Oxy-Alkylation of Allylamines with Unactivated Alkyl Bromides and CO2 via Visible-Light-Driven Palladium Catalysis

A selective oxy-alkylation of allylamines with unactivated alkyl bromides and CO₂ via visible-light-driven palladium catalysis is reported. The commercially available Pd(PPh₃)₄ is used as the sole catalyst in this three-component reaction. A variety of tertiary, secondary, and primary alkyl bromides undergo reactions to generate important 2-oxazolidinones in high yields and selectivity. The mild reaction conditions, easy scalability, and facile derivatization of products provide great potential for application in organic synthesis and pharmaceutical chemistry.

Palladium-catalyzed reductive electrocarboxylation of allyl esters with carbon dioxide

Palladium-catalyzed regioselective electrocarboxylation of homostyrenyl acetates with CO₂ has been successfully developed, providing α-aryl carboxylic acids with good selectivity and yield.