Visible-Light-Driven Reductive Carboarylation of Styrenes with CO2 and Aryl Halides

Switchable Divergent Photocatalytic C-Glycosylation of Glycosyl Benzoates

Metabolically robust C-glycosides are crucial in various biological and medical applications, underscoring the need for efficient synthesis methods. While radical C-glycosylation reactions are known for their reliability and functional group tolerance, challenges such as glycosyl donor stability and atom economy persist. In this study, we investigate the underexplored potential of condition-controlled divergent synthesis of C-glycosides through a switchable photocatalytic C-glycosylation strategy, involving reductive anomeric C─O bond cleavage. Utilizing simple, readily available, and bench-stable glycosyl benzoates as novel O-based glycosyl radical precursors, we successfully achieve deoxygenative glycosylation of simple alkenes and styryl boronic acids, establishing a versatile platform for C-glycoside synthesis. A critical aspect of the challenging reductive cleavage of these benzoate esters is the introduction of strong single-electron transfer (SET) reductants, combined with Brønsted acids to accelerate fragmentation following substrate reduction. Notably, CO2 •-, generated via the consecutive photon-induced electron transfer process, is utilized for the first time in glycosylation reactions. By meticulously tuning the reaction conditions, including photocatalysts and formate additives, we facilitate the divergent synthesis of alkyl and alkenyl C-glycosides with good to high stereoselectivity and yields. Mechanistic studies provide insight into the reaction pathway and the underlying rationale behind this finely tuned, easily controlled photocatalytic system.

Electrochemical-Thermochemical Cascade System for the Sustainable Conversion of Crude Acetylene to C6+ Esters

Acetylene (C2H2), a critical chemical feedstock derived from natural gas or coal, faces sustainability challenges due to high CO₂ emissions from conventional production methods. These emissions not only contribute to carbon footprints but also hinder the upgrading of C2H2. Herein, a two-step electrochemical and thermochemical cascade system that directly converts CO₂-contaminated crude acetylene into C6+ esters is proposed. In the first step, CO₂ from crude acetylene is captured by hydroxide to form bicarbonate, which is subsequently released in situ at the cathode under electrolysis. Using a Ni single-atom catalyst, CO is efficiently generated with a Faradaic efficiency of 97.8 ± 0.84% at 100 mA cm-2. The generated CO then reacts with acetylene in the second step, where a Pd-based catalyst enables the production of dimethyl butenedioate at 7.83 ± 0.31 mmol L-1 h-1 and selective dimethyl maleate synthesis (>65% selectivity). Furthermore, replacing methanol with ethanol or butanol in the carbonylation step allows for tunable synthesis of diethyl or dibutyl butenedioate, demonstrating broad applicability. Techno-economic analysis indicates a 46.9% cost reduction compared to the traditional reverse water-gas shift system, attributed to lower energy demands and eliminated separation steps. This work provides a green strategy for valorizing low-value acetylene streams while mitigating CO₂ emissions.

Reduction by Oxidation: Selective Hydrodehalogenation of Aryl Halides by Mediated Oxalate Oxidation

Electro-organic reduction reactions are canonically carried out at a cathode at which a significant negative potential is applied. Specifically, at carbon electrodes, aryl bromides and chlorides undergo heterogeneous reduction in organic solvents at potentials more negative than -2 V vs E0' for the Fc/Fc+ couple (Fc = ferrocene). To decrease the overpotential for reduction reactions, homogeneous or heterogeneous electrocatalysis strategies are often employed. Here, we present an electrochemical method to reduce aryl bromides and chlorides that is initiated by an oxidation reaction at very mild potentials (∼0 V vs Fc/Fc+). Specifically, electrochemical oxidation of an outer-sphere redox mediator, 1,1-dimethylferrocene, in dry N,N-dimethylformamide (DMF) containing oxalate (C2O42-), results in the homogeneous one-electron oxidation of C2O42-. The resulting C2O4•- decomposes in ∼1 μs to release the carbon dioxide radical anion (CO2•-), a potent reductant that is oxidized to CO2 at -2.68 V vs Fc/Fc+. In this way, an oxidation reaction at low electrode potentials enables homogeneous reduction of aryl bromides and chlorides, which are otherwise directly reduced at very negative potentials. Using this method, selective hydrodehalogenations of electron-deficient aryl bromides and chlorides are carried out at a reticulated vitreous carbon anode with up to quantitative conversion yields. Cyclic voltammetry and finite difference simulations are used to characterize the hydrodehalogenation of 4-bromobenzonitrile via C2O42- oxidation. Additionally, we show that the efficiency of hydrodehalogenation is tuned by deliberate additions of water to DMF solutions, leading to a substantial improvement in overall conversion yields without interference from water or proton reduction.

Photocatalytic Pyridyl-carbamoylation of Alkenes for Accessing β-Pyridyl Amides

The β-pyridyl amide is a critical scaffold in medical discovery yet lacks efficient synthetic methods. Here, we describe, for the first time, a visible-light-induced, redox-neutral radical cross-coupling reaction involving alkenes, oxamic acids, and cyanopyridines that offers a versatile assembly of β-pyridylamides. This approach features mild reaction conditions, high step efficiency, and substrate breadth, providing a green and efficient strategy for alkene pyridyl-carbamoylation. Achieving this transformation relies on the efficient catalytic system, which adeptly avoids the competing cross-coupling of the nucleophilic carbamoyl radical with the electrophilic pyridyl radical, enabling the three-component radical tandem reaction process with high chemoselectivity.

Controlled Defluorinative Carboxylation Cascade of Sterically Hindered CF3-Alkenes with Formate Salt via Photocatalysis

A controlled cleavage of double C-F bonds in sterically hindered tetrasubstituted CF3-alkenes using formate salt has been achieved through a photoinduced electron transfer approach. Diverse γ-branched multifunctionalized gem-difluoroalkenes and α-fluoroacrylic acids are obtained sequentially via hydrodefluorination and C-F bond carboxylation with good-to-high yields. Precisely controlling the quantity of formate salt and the reaction time is crucial for obtaining divergent defluorinative products. Formate serves as the C1 source, hydrogen donor, and reducing agent.

Photocatalyst-free formate-mediated C-O cleavage by the EDA complex and SCS strategy for the synthesis of diaryl 1,4-diketone in air

Under mild visible light conditions, formates facilitate C-O cleavage via the EDA complex and SCS strategy, yielding α-carbonyl alkyl radicals. These radicals then react with olefins under air conditions, leading to the synthesis of diaryl 1,4-dicarbonyl compounds. Mechanistic studies reveal that α-formyloxy ketone is generated in situ by the reaction between α-brominated acetophenone and formates, followed by the formation of the EDA complex. Additionally, formates also serve as a single-electron reducing reagent in the reaction.

Metallaphotoredox-catalyzed alkynylcarboxylation of alkenes with CO2 and alkynes for expedient access to β-alkynyl acids

Carboxylation with CO2 offers an attractive and sustainable access to valuable carboxylic acids. Among these methods, direct C-H carboxylation of terminal alkynes with CO2 has attracted much attention for one-carbon homologation of alkynes, enabling rapid synthesis of propiolic acids. In contrast, the multi-carbons homologation of alkynes with CO2 to construct important non-conjugated alkynyl-containing acids has not been reported. Herein, we present alkynylcarboxylation of alkenes with CO2 via photoredox and copper dual catalysis. This protocol provides a direct and practical method to form valuable non-conjugated alkynyl acids from readily available alkynes, alkenes and CO2. Additionally, this approach also features mild (room temperature, 1 atm of CO2) and redox-neutral conditions, high atom and step economy, good functional group tolerance, and high selectivities. Moreover, diverse transformations of the β-alkynyl acid products and the rapid synthesis of bioactive molecule (GPR40/FFA1 agonist) further illustrate the synthetic utility of this methodology.

Visible-Light-Driven Carboxylative 1,2-Difunctionalization of C=C Bonds with Tetrabutylammonium Oxalate

Herein, we report a visible-light-induced charge-transfer-complex-enabled dicarboxylation and deuterocarboxylation of C=C bonds with oxalate as a masked CO2 source under catalyst-free conditions. In this reaction, we disclosed the first example that the tetrabutylammonium oxalate could be able to aggregate with aryl substrates via π-cation interactions to form the charge transfer complexes, which subsequently triggers the single electron transfer from the oxalic dianion to the ammonium countercation under irradiation of 450 nm bule LEDs, releasing CO2 and CO2 radical anions. Diverse alkenes, dienes, trienes, and indoles, including challenging trisubstituted olefins, underwent dicarboxylation and anti-Markovnikov deuterocarboxylation with high selectivity to access valuable 1,2- and 1,4-dicarboxylic acids as well as indoline-derived diacids and β-deuterocarboxylic acids under mild conditions. The in situ generated CO2 •- and CO2 molecules from oxalic radical anions could both add to the C=C bond without assistance of any photocatalyst or additives, which made this reaction sustainable, clean, and efficient.

Nickel-Catalyzed Atroposelective Carbo-Carboxylation of Alkynes with CO2: En Route to Axially Chiral Carboxylic Acids

Precise synthesis of carboxylic acids via catalytic carboxylation with CO2 is highly appealing. Although considerable advancements have been achieved in difunctionalizing carboxylation of unsaturated hydrocarbons, the asymmetric variants are conspicuously underdeveloped, particularly in addressing axially chiral alkenes. Herein, we report the first catalytic atroposelective carboxylation of alkynes with CO2. A variety of valuable axially chiral carboxylic acids are obtained with good yields and high chemo-, regio-, Z/E and enantio-selectivities. Notably, an unexpected anti-selective carbo-carboxylation is observed in the sp2-hybrid carbo-electrophile-initiated reductive carboxylation of alkynes. Mechanistic studies including DFT calculation elucidate the origin of chiral induction and anti-selectivity in vinyl-carboxylation of alkynes.

Light-assisted functionalization of aryl radicals towards metal-free cross-coupling

The many synthetic possibilities that arise when using radical intermediates, in place of their polar counterparts, make contemporary radical chemistry research an exhilarating field. The introduction of photocatalysis has helped tame aryl radicals, leading to a resurgence of interest in their chemistry, and an expansion of viable coupling partners and attainable transformations. These methods are more selective and safer than classical approaches, and they utilize new radical precursors. Given the importance of sustainability in current organic synthesis and our interest in light-assisted metal-free transformations, this Review focuses on recent advances in the use of aryl radicals in photoinduced cross-couplings that do not rely on metals for the crucial bond-forming event, and it is structured according to the key step that the aryl radicals engage in.

Remote C(sp3)-H Carboxylation with CO2 via Visible-Light-Catalyzed 1,5-Hydrogen Atom Transfer

The direct carboxylation of C(sp3)-H bonds with CO2 represents a challenging but highly attractive strategy in organic synthesis. In this study, we presented a visible-light-catalyzed strategy for carboxylating remote C(sp3)-H bonds with CO2 via aryl radical induced 1,5-hydrogen atom transfer. This transformation involves generating alkyl radicals via 1,5-hydrogen atom transfer from aryl radicals, forming alkyl carbanions as key intermediates, and a subsequent nucleophilic attack with CO2, thereby enabling access to a variety of tertiary and quaternary carboxylic acids in moderate to good yields.

Alkene Carboxy-Alkylation via CO2•

Herein, we introduce a new platform for alkene carboxy-alkylation. This reaction is designed around CO2•- addition to alkenes followed by radical polar crossover, which enables alkylation through carbanion attack on carbonyl electrophiles. We discovered that CO2•- adds to alkenes faster than it reduces carbonyl electrophiles and that this reactivity can be exploited by accessing CO2•- via hydrogen atom transfer from formate. This photocatalytic system transforms vinylarenes and carbonyl compounds into a diverse array of substituted γ-lactone products. Furthermore, indoles can be engaged through dearomative carboxy-alkylation, delivering medicinally relevant C(sp3)-rich heterocyclic scaffolds. Mechanistic studies reveal that the active photocatalyst is generated in situ through a photochemically induced reaction between the precatalyst and DMSO. Overall, we have developed a three-component alkene carboxy-alkylation reaction enabled by the use of formate as the CO2•- precursor.

Photoredox-Catalyst-Free Carboxylation of Unactivated Alkenes in DMSO: Synthesis of Polycyclic Indole Derivatives and Aliphatic Acids

A new method for the carboxylation of unactivated alkenes using CO2 radical anions in the absence of a photoredox catalyst has been developed. The photocatalyst-free approach enables the efficient synthesis of polycyclic indole derivatives and linear carboxylic acids under mild conditions from HCO2K with/without 1,4-diazabicyclo[2.2.2]octane (DABCO) in DMSO. This work demonstrates a significant advance in green chemistry, showcasing a catalyst-free approach for the functionalization of unactivated alkenes with cheap and readily available HCO2K.

Visible-Light-Mediated Nucleophilic Addition of Alkene with Aldehyde: Synthesis of Secondary Alcohols

Herein, a photocatalytic strategy for the synthesis of secondary alcohols by nucleophilic addition of an alkene with an aldehyde is described. This operationally simple methodology opens an approach for the synthesis of alcohols using commercially available reagents in moderate to excellent yields. Mechanistic studies indicate that the formation of the radical anion from alkene via single-electron transfer is the key step in this reaction.

Base-promoted cascade 5-exo-dig annulation/carboxylation of o-(1-alkynyl)benzenesulfonamides with CO2: divergent synthesis of mono- or gem-dicarboxylic esters

A base-promoted cascade 5-exo-dig cyclization/carboxylation of o-alkynylsulfamides with CO2 has been accomplished, furnishing a variety of benzosultam-containing acrylates in good yields by using CO2 as the carboxylic source. Notably, in the case of substrates bearing a TMS-alkyne motif, the gem-dicarboxylation products were generated unprecedentedly.

Visible-Light-Promoted Reduction of Nitroarenes with Formate Salts as Reductants

A visible-light-promoted reduction of nitrobenzenes using formate salts as the reductant was developed. A wide range of nitrobenzenes can be converted into aniline products in a transition metal free fashion. Mechanistic studies revealed that radical species (carbon dioxide radical anion and thiol radical) are key intermediates for the transformation. We anticipate that this method will provide a valuable and green strategy for the reduction of nitrobenzenes.

Photo-induced carboxylation of C(sp2)-S bonds in aryl thiols and derivatives with CO2

Aryl thiols have proven to be a useful class of electron donors and hydrogen atom sources in photochemical processes. However, the direct activation and functionalization of C(sp2)-S bonds in aryl thiols remains elusive in the field of photochemistry. Herein, a photochemical carboxylation of C(sp2)-S bonds in aryl thiols with CO2 is reported, providing a synthetic route to important aryl carboxylic acids. Moreover, different kinds of aryl thiol derivatives, benzeneselenol and diphenyl diselenide also show moderate-to-high reactivity in this transformation. Mechanistic studies, including DFT calculations, suggest that the in situ generated carbon dioxide radical anion (CO2•-) and disulfide might be the key intermediates, which undergo radical substitution to yield products. This reaction features mild and catalyst-free conditions, good functional group tolerance and wide substrate scope. Furthermore, the efficient degradation of polyphenylene sulfide highlights the usefulness of this methodology.

Taming CO2•- via Synergistic Triple Catalysis in Anti-Markovnikov Hydrocarboxylation of Alkenes

The direct utilization of carbon dioxide as an ideal one-carbon source in value-added chemical synthesis has garnered significant attention from the standpoint of global sustainability. In this regard, the photo/electrochemical reduction of CO2 into useful fuels and chemical feedstocks could offer a great promise for the transition to a carbon-neutral economy. However, challenges in product selectivity continue to limit the practical application of these systems. A robust and general method for the conversion of CO2 to the polarity-reversed carbon dioxide radical anion, a C1 synthon, is critical for the successful valorization of CO2 to selective carboxylation reactions. We demonstrate herein a hydride and hydrogen atom transfer synergy driven general catalytic platform involving CO2•- for highly selective anti-Markovnikov hydrocarboxylation of alkenes via triple photoredox, hydride, and hydrogen atom transfer catalysis. Mechanistic studies suggest that the synergistic operation of the triple catalytic cycle ensures a low-steady-state concentration of CO2•- in the reaction medium. This method using a renewable light energy source is mild, robust, selective, and capable of accommodating a wide range of activated and unactivated alkenes. The highly selective nature of the transformation has been revealed through the synthesis of hydrocarboxylic acids from the substrates bearing a hydrogen atom available for intramolecular 1,n-HAT process as well as diastereoselective synthesis. This technology represents a general strategy for the merger of in situ formate generation with a synergistic photoredox and HAA catalytic cycle to provide CO2•- for selective chemical transformations.

Photoinduced Radical Approach for Desulfurative Alkylation of Cysteine Derivatives to Make Unnatural Amino Acids

Unnatural amino acids (UAAs) are highly valuable molecules in organic synthesis, pharmaceutical sciences, and material science. Herein, we present a photocatalytic radical approach for desulfurative alkylation of cysteine derivatives with arenethiol as the hydrogen atom transfer catalyst for making UAAs and peptides. The formate salt, acting as the hydrogen atom donor, in situ generates the highly reductive CO2 radical anion species, which is the key to unlocking the C-S bond cleavage process with a simple benzoyl protecting group. No photocatalyst is required for the radical initiation and propagation, which makes such a visible-light-induced process mild, efficient, and sustainable.

Visible-Light Photoredox-Catalyzed Direct Carboxylation of Tertiary C(sp3)-H Bonds with CO2: Facile Synthesis of All-Carbon Quaternary Carboxylic Acids

Direct carboxylation of C-H bonds with CO2 represents an attractive strategy to synthesize valuable carboxylic acids with high atom, step, and redox economy. Although great progress has been achieved in this field, catalytic carboxylation of tertiary C(sp3)-H bonds still remains challenging due to their inherent inertness and significant steric hindrance. Herein, we report a direct carboxylation of tertiary benzylic C(sp3)-H bonds with CO2 via visible-light photoredox catalysis. Various all-carbon quaternary carboxylic acids, which are of significant importance in medicinal chemistry, are successfully obtained with high yields. This direct carboxylation is characterized by good functional group tolerance, broad substrate scope, and mild operational conditions. Furthermore, our methodology enables the efficient and rapid synthesis of key drug or bioactive molecules, such as carbetapentane, caramiphen, and PRE-084 (σ1 receptor agonist), and facilitates various functionalizations of C(sp2)-H bonds using the directing ability of target carboxylic acids, thus highlighting its practical applications. Mechanistic studies indicate that a carbanion, which serves as the key intermediate to react with CO2, is catalytically generated via a single electron reduction of a benzylic radical through a consecutive photoinduced electron transfer process.

Light-Driven Formate-Salts-Induced Cleavage of Oxidized Lignin Model Compounds

We report a light-induced cleavage of oxidized lignin model compounds utilizing formate salts. For compounds containing an aliphatic hydroxyl (γ-OH) group, the employment of a hydrogen atom transfer (HAT) catalyst was crucial to preserving the efficacy of the fragmentation reaction. Furthermore, we successfully converted a trimeric oxidized model compound into the desired products with moderate yields.

Photocatalytic deuterocarboxylation of alkynes with oxalate

Herein, a catalytic photoredox-neutral strategy for alkyne deuterocarboxylation with tetrabutylammonium oxalate as the carbonyl source and D2O as the deuteration agent was described. For the first time, the oxalic salt acted as both the reductant and carbonyl source through single electron transfer and subsequential homolysis of the C-C bond. The strongly reductive CO2 radical anion species in situ generated from oxalate played significant roles in realizing the global deuterocarboxylation of terminal and internal alkynes to access various tetra- and tri-deuterated aryl propionic acids with high yields and deuteration ratios.

Harnessing Bromo/Acyloxy Transposition (BrAcT) and Excited-State Copper Catalysis for Styrene Difunctionalization

1,2-Difunctionalization of styrenes, adding two distinct functional groups across the C═C double bond, has emerged as a powerful tool for enhancing molecular complexity. Herein, we report the development of a regioconvergent β-acyloxylation-α-ketonylation of styrenes through bromo/acyloxy transposition (BrAcT) and excited-state copper catalysis. This approach is amenable to gram-scale synthesis and tolerates a wide range of functional groups and complex molecular frameworks, including derivatives of natural products and marketed drugs. Our experimental and computational studies suggest a unique mechanism featuring a dynamic, ionic BrAcT process and excited-state copper-catalyzed redox reactions. We anticipate that this BrAcT process could serve as a broadly applicable and versatile strategy for β-acyloxylation-α-functionalization of styrenes, creating valuable intermediates for preparing new pharmaceuticals, agrochemicals, and functional materials.

Visible-Light-Promoted Cascade Carboxylation/Arylation of Unactivated Alkenes with CO2 for the Synthesis of Carboxylated Indole-Fused Heterocycles

Described here is a visible-light-promoted cascade carboxylation/arylation of indole-tethered unactivated alkenes with CO2 to access various carboxylated indole-fused heterocycles. This reaction is initiated by the addition of a CO2 radical anion to the alkene motif toward an alkyl carbon radical, followed by its addition to the aromatic ring, and then rearomatization to afford the final products. This reaction provides a facile and sustainable protocol for the construction of carboxylated indole-fused heterocycles using CO2 as the carboxylic source.

Photocatalytic Three-Component Acylcarboxylation of Alkenes with CO2

γ-Keto acid is a valuable chemical motif in a wide range of fields including organic, biological, and medicinal chemistry. However, its single-step synthesis is challenging because of the mismatch of the carbonyl polarity and low tolerance of carboxylic acids. Herein, we report the single-step syntheses of γ-keto acids using alkenes and CO2. Our photocatalytic system enabled the transformation of alkenes under mild conditions in high yields (up to 95%) with broad substrate generality (35 examples).

Formate and CO2 Enable Reductive Carboxylation of Imines: Synthesis of Unnatural α-Amino Acids

Herein, a photocatalytic umpolung strategy for reductive carboxylation of imines for the synthesis of α-amino acids was disclosed. Carbon dioxide radical anion (CO2•-) generated from formate is the key single electron reductant in the reactions. An unprecedentedly broad substrate scope of imines with excellent reaction yields was obtained with carbon dioxide (CO2) and formate salt as carbon sources.

Catalytic Regio- and Enantioselective Remote Hydrocarboxylation of Unactivated Alkenes with CO2

The catalytic regio- and enantioselective hydrocarboxylation of alkenes with carbon dioxide is a straightforward strategy to construct enantioenriched α-chiral carboxylic acids but remains a big challenge. Herein we report the first example of catalytic highly enantio- and site-selective remote hydrocarboxylation of a wide range of readily available unactivated alkenes with abundant and renewable CO2 under mild conditions enabled by the SaBOX/Ni catalyst. The key to this success is utilizing the chiral SaBOX ligand, which combines with nickel to simultaneously control both chain-walking and the enantioselectivity of carboxylation. This process directly furnishes a range of different alkyl-chain-substituted or benzo-fused α-chiral carboxylic acids bearing various functional groups in high yields and regio- and enantioselectivities. Furthermore, the synthetic utility of this methodology was demonstrated by the concise synthesis of the antiplatelet aggregation drug (R)-indobufen from commercial starting materials.

Electroreductive Arylcarboxylation of Styrenes with CO2 and Aryl Halides via a Radical-Polar Crossover Mechanism

2,3-Diaryl propanoic acids are important structures as a result of their widespread presence in numerous bioactive compounds. However, the limitations of existing synthetic techniques include the requirement for costly catalysts and limited substrates. Here, we developed a novel electroreductive arylcarboxylation of alkenes with CO2 based on a radical-polar crossover pathway assisted by easily accessible dimethyl terephthalate as a reductive mediator. This method will provide an efficient strategy for the synthesis of 2,3-diarylpropanoic 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.

Recent Advances in Dearomative Partial Reduction of Benzenoid Arenes

Dearomative partial reduction is an extraordinary approach for transforming benzenoid arenes and has been well-known for many decades, as exemplified by the dehydrogenation of Birch reduction and the hydroarylation of Crich addition. Despite its remarkable importance in synthesis, this field has experienced slow progress over the last half-century. However, a revival has been observed with the recent introduction of electrochemical and photochemical methods. In this Minireview, we summarize the recent advancements in dearomative partial reduction of benzenoid arenes, including dihydrogenation, hydroalkylation, arylation, alkenylation, amination, borylation and others. Further, the intriguing utilization of dearomative partial reduction in the synthesis of natural products is also emphasized. It is anticipated that this Minireview will stimulate further progress in arene dearomative transformations.

A MOF nanoparticle@carbon aerogel integrated photothermal catalytic microreactor for CO2 utilization

A practical carbon dioxide (CO2) conversion and utilization system shows great potential for ameliorating the greenhouse effect. Herein, an integrated carbon aerogel-based photothermal catalysis microreactor with photothermal conversion, enhanced mass transfer adsorption and a thermal catalytic reactor is designed. As a solar-powered CO2 utilization module, this microreactor can conveniently convert CO2 into economically valuable products without elaborate equipment and operation processes.

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.

Capture and Utilization of CO2 with Morpholine for Effective Photocatalytic N-Formylmorpholine Production

Converting into high-value-added products represents the most optimal approach to CO2 utilization. The substitution of CO with CO2 as a potential critical material for formamide production is widely regarded as an ideal pathway and has garnered significant attention. However, high temperatures and pressures remain essential for the reaction, exerting a substantial influence on the utilization process. Herein, N-formylmorpholine was creatively synthesized by integrating the capture and solar-driven utilization of CO2 with morpholine. Notably, a remarkable N-formylmorpholine yield of 11433.3 μmol·h-1·g-1 was obtained, surpassing pure MoO3 by an astounding factor of 89.1 with a N-formylmorpholine yield of 63.8 μmol in 6 h, which is an astonishing increase of 57.5 times compared to MoO3. Both experimental results and density functional theory calculations suggest that the inclusion of Fe can effectively reduce the formation energy barrier while facilitating the desorption process of N-formylmorpholine, thereby optimizing the overall performance.

Photoelectrocatalytic Utilization of CO2 : A Big Show of Si-based Photoelectrodes

CO2 is a greenhouse gas that contributes to environmental deterioration; however, it can also be utilized as an abundant C1 resource for the production of valuable chemicals. Solar-driven photoelectrocatalytic (PEC) CO2 utilization represents an advanced technology for the resourcing of CO2 . The key to achieving PEC CO2 utilization lies in high-performance semiconductor photoelectrodes. Si-based photoelectrodes have attracted increasing attention in the field of PEC CO2 utilization due to their suitable band gap (1.1 eV), high carrier mobility, low cost, and abundance on Earth. There are two pathways to PEC CO2 utilization using Si-based photoelectrodes: direct reduction of CO2 into small molecule fuels and chemicals, and fixation of CO2 with organic substrates to generate high-value chemicals. The efficiency and product selectivity of PEC CO2 utilization depends on the structures of the photoelectrodes as well as the composition, morphology, and size of the catalysts. In recent years, significant and influential progress has been made in utilizing Si-based photoelectrodes for PEC CO2 utilization. This review summarizes the latest research achievements in Si-based PEC CO2 utilization, with a particular emphasis on the mechanistic understanding of CO2 reduction and fixation, which will inspire future developments in this field.

Single electron reduction of NHC-CO2-borane compounds

The carbon dioxide radical anion [CO2˙-] is a highly reactive species of fundamental and synthetic interest. However, the direct one-electron reduction of CO2 to generate [CO2˙-] occurs at very negative reduction potentials, which is often a limiting factor for applications. Here, we show that NHC-CO2-BR3 species - generated from the Frustrated Lewis Pair (FLP)-type activation of CO2 by N-heterocyclic carbenes (NHCs) and boranes (BR3) - undergo single electron reduction at a less negative potential than free CO2. A net gain of more than one volt was notably measured with a CAAC-CO2-B(C6F5)3 adduct, which was chemically reduced to afford [CAAC-CO2-B(C6F5)3˙-]. This room temperature stable radical anion was characterized by EPR spectroscopy and by single-crystal X-ray diffraction analysis. Of particular interest, DFT calculations showed that, thanks to the electron withdrawing properties of the Lewis acid, significant unpaired spin density is localised on the carbon atom of the CO2 moiety. Finally, these species were shown to exhibit analogous reactivity to the carbon dioxide radical anion [CO2˙-] toward DMPO. This work demonstrates the advantage provided by FLP systems in the generation and stabilization of [CO2˙-]-like species.

Characterization of A π-π stacking cocrystal of 4-nitrophthalonitrile directed toward application in photocatalysis

Photoexcitation of the electron-donor-acceptor complexes have been an effective approach to achieve radicals by triggering electron transfer. However, the catalytic version of electron-donor-acceptor complex photoactivation is quite underdeveloped comparing to the well-established utilization of electronically biased partners. In this work, we utilize 4-nitrophthalonitrile as an electron acceptor to facilitate the efficient π-stacking with electron-rich aromatics to form electron-donor-acceptor complex. The characterization and energy profiles on the cocrystal of 4-nitrophthalonitrile and 1,3,5-trimethoxybenzene disclose that the electron transfer is highly favorable under the light irradiation. This electron acceptor catalyst can be efficiently applied in the benzylic C-H bond photoactivation by developing the Giese reaction of alkylanisoles and the oxidation of the benzyl alcohols. A broad scope of electron-rich aromatics can be tolerated and a mechanism is also proposed. Moreover, the corresponding π-anion interaction of 4-nitrophthalonitrile with potassium formate can further facilitate the hydrocarboxylation of alkenes efficiently.

Transition-Metal-Free Anti-Markovnikov Hydroarylation of Alkenes with Aryl Chlorides through Consecutive Photoinduced Electron Transfer

The hydroarylation of alkenes has emerged as a powerful strategy for arene functionalization. However, aryl chlorides remain a large challenge in this type of reaction due to the chemical inertness of the C(sp2)-Cl bond and high negative reduction potential. Herein, we report an anti-Markovnikov radical hydroarylation of alkenes with aryl chlorides via visible-light photoredox catalysis. The key reactive aryl radicals can be efficiently achieved from aryl chlorides by consecutive photoinduced electron transfer. This transition-metal-free protocol features mild conditions, a wide substrate scope, and functional group tolerance, producing a diverse range of linear alkylarenes in moderate to good yields. The reaction is proposed to proceed through a radical-polar crossover pathway.

Photochemical Deoxygenative Hydroalkylation of Unactivated Alkenes Promoted by a Nucleophilic Organocatalyst

The direct utilization of simple and abundant feedstocks in carbon-carbon bond-forming reactions to embellish sp3 -enriched chemical space is highly desirable. Herein, we report a novel photochemical deoxygenative hydroalkylation of unactivated alkenes with readily available carboxylic acid derivatives. The reaction displays broad functional group tolerance, accommodating carboxylic acid-, alcohol-, ester-, ketone-, amide-, silane-, and boronic ester groups, as well as nitrile-containing substrates. The reaction is operationally simple, mild, and water-tolerant, and can be carried out on multigram-scale, which highlights the utility of the method to prepare value-added compounds in a practical and scalable manner. The synthetic application of the developed method is further exemplified through the synthesis of suberanilic acid, a precursor of vorinostat, a drug used for the treatment of cutaneous T-cell lymphoma. A novel mechanistic approach was identified using thiol as a nucleophilic catalyst, which forms a key intermediate for this transformation. Furthermore, electrochemical studies, quantum yield, and mechanistic experiments were conducted to support a proposed catalytic cycle for the transformation.

Visible-Light-Induced Synthesis of 1,2-Dicarboxyl Compounds from Carbon Dioxide, Carbamoyl-dihydropyridine, and Styrene

β-Amidated carboxylic acids, or succinamic acid derivatives, constitute a valuable chemical scaffold with broad applications in pharmaceuticals, agrochemicals, and polymer sciences. Herein, we report a redox-neutral multicomponent reaction for the synthesis of succinamic acid derivatives in good yields. This protocol involves styrene, CO2 and 1,4-carbamoyl-dihydropyridine as radical precursors. The method exhibits a broad substrate scope under mild reaction conditions, including late-stage functionalization. Moreover, by employing 13CO2, the method enables the synthesis of labeled 1,2-dicarboxylic compounds.

Photoredox-Catalyzed Defluorinative Carboxylation of gem-Difluorostyrenes with Formate Salt

Herein, we present a transition-metal-free, easy handling protocol for regioselective carboxylation of gem-difluorostyrenes with sodium formate as the C1 source. 30 examples of α-fluoracrylates were obtained in yields of 30 to 80% under these conditions. A defluorinative monofluorovinyl intermediate and consecutive photoinduced electron transfer mechanism were proposed after mechanism investigation.

Reductive Radical-Polar Crossover Enabled Carboxylative Alkylation of Aryl Thianthrenium Salts with CO2 and Styrenes

Carboxylic functionalities are among the pivotal groups in bioactive molecules and in the synthesis of new lead compounds because of their unique character in the formation of hydrogen bonds and the possibility of constructing molecular complexes via amide couplings. We adopt the reductive radical-polar crossover strategy to introduce carboxyalkyl groups into arenes with styrenes and CO2 via thianthrenium salts. This protocol exhibits excellent potential as a straightforward and modular platform for site-selective carboxylative derivation of bioactive molecules.

Visible-light-driven photocatalytic carboxylation to aromatic carboxylic acids with CO2

(Hetero)aromatic carboxylic acids and their derivatives attract attention due to their role in the synthesis of several biologically active molecules, active pharmaceutical ingredients, polymers, etc. Carbon dioxide (CO2) is a prime C1 source for the synthesis of aromatic carboxylic acids because of its nontoxicity, nonflammability, abundance and renewability. Owing to the thermodynamic and chemical inertness of CO2, traditional carboxylation to aromatic carboxylic acids with CO2 is always performed under harsh reaction conditions or using stoichiometric metallic reductants. Visible-light-driven carboxylation with CO2 provides an environmentally benign, mild, and high-efficiency route for the production of aromatic carboxylic acids. This review comprehensively introduces the visible-light-driven preparation of aromatic carboxylic acids through a visible-light-driven oxidative addition and reductive elimination mechanism, binding of aryl (radical) anions which are produced by photoinduced electron transfer (PET) to CO2, binding of carbon dioxide anion radicals (CO2˙-) which are formed by PET to aryl compounds, radical coupling between CO2˙- and aryl radicals, and other mechanisms. Finally, this review provides a summary and the future work direction. This article offers a theoretical guidance for efficient synthesis of aromatic carboxylic acids via photocatalysis.

Recent Discovery, Development, and Synthetic Applications of Formic Acid Salts in Photochemistry

The advancement of sustainable photoredox catalysis in synthetic organic chemistry has evolved immensely because of the development of versatile and cost-effective reagents. In recent years, a substantial effort has been dedicated to exploring the utility of formic acid salts in various photochemical reactions. In this context, formates have demonstrated diverse capabilities, functioning as reductants, sources of carbonyl groups, and reagents for hydrogen atom transfer. Notably, the CO2 ⋅- radical anion derived from formate exhibits strong reductant properties for cleaving both C-X and C-O bonds. Moreover, these salts play a pivotal role in carboxylation reactions, further highlighting their significance in a variety of photochemical transformations. The ability of formates to serve as reductants, carbonyl sources, and hydrogen atom transfer reagents reveal exciting possibilities in synthetic organic chemistry. This minireview highlights an array of captivating discoveries, underscoring the crucial role of formates in diverse and distinctive photochemical methods, enabling access to a wide range of value-added compounds.

Metal-Free Heterogeneous Photocatalysis for Carbocarboxylation of Alkenes: Efficient Synthesis of γ-Amino Carboxylic Derivatives

A metal-free heterogeneous protocol is established herein for the synthesis of value-added γ-amino acid scaffolds via carbocarboxylation of alkenes with CO2 and alkylamines under visible light irradiation. The protocol shows broad substrate scope under mild reaction conditions and good stability of the catalyst for recycle tests. Moreover, the methodology could be feasible to the late-stage derivatization of several natural products, enriching the chemical arsenal for practical application.

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.

Photo- and electro-chemical strategies for the activations of strong chemical bonds

The employment of light and/or electricity - alternatively to conventional thermal energy - unlocks new reactivity paradigms as tools for chemical substrate activations. This leads to the development of new synthetic reactions and a vast expansion of chemical spaces. This review summarizes recent developments in photo- and/or electrochemical activation strategies for the functionalization of strong bonds - particularly carbon-heteroatom (C-X) bonds - via: (1) direct photoexcitation by high energy UV light; (2) activation via photoredox catalysis under irradiation with relatively lower energy UVA or blue light; (3) electrochemical reduction; (4) combination of photocatalysis and electrochemistry. Based on the types of the targeted C-X bonds, various transformations ranging from hydrodefunctionalization to cross-coupling are covered with detailed discussions of their reaction mechanisms.

Organophotocatalyzed Mono- and Bis-Alkyl/Difluoroalkylative Thio/Selenocyanation of Alkenes

Organophotocatalyzed three-component 1,2-difluoroacetyl/alkyl/perfluoroalkylative thio/selenocyanation of styrene derivatives under stoichiometric, transition metal-, oxidant-, and additive-free, and mild redox-neutral conditions is reported. Organophotocatalyst 4CzIPN operates the overall radical-polar-crossover mechanistic cycle via initial oxidative luminescence quenching, and the key intermediates were experimentally detected. Selective mono-alkylative thiocyanation of alkenes using dibromoalkanes is also demonstrated. This one-pot synthetic methodology is suitable for primary, secondary, and tertiary alkyl halides and also extended for double alkylative thiocyanation of the dibromoalkanes with excellent yields.

Visible Light Induced Three-Component 1,2-Dicarbofunctionalization of Alkenes and Alkynes

Harnessing visible-light in organic synthesis is one of the most effective methods that aligns with green and sustainable chemistry principles and hence skyrocketed in the last two decades. Similarly, three-component 1,2-dicarbofunctionalization of alkenes and alkynes has recently been a great choice to construct complex molecular systems in an easy and rapid manner. Therefore, light-induced reactions can be an excellent alternative to carry out 1,2-dicarbofunctionalization reactions, and very recently, organic chemists across the globe have fascinated us with their interesting articles. In this present review, we have summarized the recent advancements in the area of visible light induced three-component 1,2-dicarbofunctionalization of alkenes and alkynes till March 2023. We have categorized the discussion based on the catalysts used to carry out the transformations for better understanding and different important aspects of these transformations have also been covered.

Photoredox-Catalyzed Phosphonocarboxylation of Allenes with Phosphine Oxides and CO2

Phosphonocarboxylation of allenes with diarylphosphine oxides and CO2 via visible-light photoredox catalysis was developed for the first time. This work provided practical and sustainable access to highly valuable but otherwise difficult-to-access linear allylic β-phosphonyl carboxylic acids in moderate yields with exclusive regio- and stereoselectivity. This method was also characterized by step and atom economy and transition-metal free and mild conditions. Preliminary mechanistic studies suggested that allyl-methyl carbanion species are the key intermediates.