Photoelectrochemical Asymmetric Catalysis Enables Direct and Enantioselective Decarboxylative Cyanation

Paired Chemical Upgrading in Photoelectrochemical Cells

Photoelectrochemical (PEC) technology has emerged as a promising platform for sustainable energy conversion and chemical synthesis, utilizing solar energy to facilitate redox reactions. While PEC systems have been extensively studied for water splitting, CO2 reduction, nitrogen reduction for value-added compounds synthesis, the sluggish oxygen evolution reaction (OER) on the anode side and the less economic value of O2 limit system efficiency. To address this, researchers have explored paired chemical upgrading strategies, coupling selective anodic organic oxidation reactions (OORs) with cathodic reduction reactions. This approach enabled the simultaneous production of high-value chemicals and fuels, enhancing the PEC system efficiency and economic viability. In this Perspective, we highlight the latest advancements and milestones in coupling anode OORs and cathode reduction reactions within PEC cells. Particular emphasis is placed on the key design principles, catalyst development, reaction mechanisms, and the performance of paired PEC cells. In addition, challenges and perspectives are provided for the future development of this emerging and sustainable technology.

Electrochemical C-H Hydroxylation and Alkoxylation Reactions

The electrochemical C-H hydroxylation and alkoxylation reactions have emerged as sustainable platforms to construct valuable oxygenated compounds such as alcohols, phenols, and ethers. Compared with traditional approaches, these electrochemical strategies not only enhance the atom economy through bypassing the use of chemical oxidants but also unlock new reactivities by accessing reactive intermediates under mild conditions. In this review, we tried to provide an overview of the representative achievements in this field since 2020. The related transformations are classified into five parts according to the underlying mechanisms. Furthermore, the potential opportunities and challenges within this rapidly emerging field were also discussed. This review is not intended to be exhaustive but rather to illustrate the synthetic potential of electrochemical C-H hydroxylation and alkoxylation strategies in the sustainable and selective assembly of valuable oxygenated compounds.

Photoelectrocatalyzed Alkylation of Phosphonites by Direct Decarboxylative C(sp3)-P Coupling

A photoelectrocatalytic method is presented that achieves direct decarboxylative C(sp3)-P coupling, providing a modular route to alkylphosphinates and alkylphosphonates from readily available carboxylic acids. The success of this reaction hinges on the synergistic combination of electrochemical anodic oxidation and photocatalytic ligand to metal charge transfer (LMCT) decarboxylation. By employing P(III) reagents as limiting reagents, our approach enables efficient alkyl modification of medicinally important nucleosides and complex molecules derived phosphonites, which were challenging to access by existing methods. Detailed mechanistic studies elucidate the critical roles of Fe catalysts and additives, offering valuable insights into the reaction pathway and laying the foundation for future advancements in photoelectrocatalytic C(sp3)-heteroatom bond-forming reactions.

Enantioselective electrochemical nickel-catalyzed vinylogous radical reactions

Highly functionalized structural motifs with extended chiral carbon chains are prevalent in a wide range of bioactive compounds and play critical roles in the production of various functionalized molecules. Here, we describe a nickel-catalyzed asymmetric radical-based electrochemical functionalization of silyl polyenolates at α-, γ-, ε-, and η-positions. Driven by electric current, this methodology provides a sustainable route to access enantioenriched dicarbonyls via vinylogous radical pathways. It demonstrates excellent functional groups tolerance, mild reaction conditions, broad substrate compatibility, formation of quaternary stereocenters at remote positions, and high levels of regio- and enantioselectivity (up to 98% enantiomeric excess). Mechanistic investigations indicate that ferrocene-based electron transfer mediators are pivotal in the anodic oxidation process, facilitating the generation of nickel-bound α-carbonyl radicals while suppressing the undesired oxidation of silyl polyenolates, thus guiding the selection of mediators for electrocatalytic systems. The versatility of catalytic asymmetric electrosynthesis is highlighted by the preparation of valuable enantioenriched building blocks and the total synthesis of (-)-ethosuximide.

Enantioselective Multicomponent Electrochemical Difunctionalization of Terminal Alkynes

The direct functionalization of alkyne triple bonds using a radical strategy provides an efficient platform for creating a wide range of substituted alkenes. However, developing a multicomponent enantioselective radical reaction using feedstock alkynes to forge all-carbon quaternary stereocenters─while addressing challenges related to compatibility, selectivity, and efficiency─remains relatively rare. Here we report an enantioselective electrochemical nickel-catalyzed three-component cross-coupling of readily available terminal alkynes, diverse racemic alkyl radical precursors, and group transfer reagents (such as (TMS)3Si-H, RSe-SeR, RTe-TeR, and CHI3), achieving excellent regio-, stereo-, and enantioselectivities (more than 70 examples, up to 95% ee). Electricity-mediated difunctionalizations significantly expand the scope of both aliphatic and aromatic alkynes, demonstrating excellent functional group compatibility. The key to success lies in the rational design of anodically generated nickel-bound tertiary radical intermediates, which stereoselectively capture alkynes to form vinyl radicals and participate in subsequently diverse group transfer processes to enable the intermolecular and anti-stereoselective difunctionalization of alkynes. This approach allows the transformation of terminal alkynes into diverse structural entities with α-quaternary stereogenic centers.

Unlocking HFIP for Fluoroalkylation with Molecular Photoelectrocatalysis

Despite the increasing interest in radical-based fluoroalkylation techniques, the organofluorine compounds bearing the partially fluorinated hexafluoroisopropyl group remain extremely scarce due to the lack of appropriate reagents. Herein we report an unprecedented photoelectrocatalytic method for the C-H hexafluoroisopropylation of indoles and tryptophan peptides, utilizing the readily available hexafluoro-2-propanol (HFIP) as the fluoroalkylation reagent. In this process, HFIP is converted into hexafluoroisopropyl radicals, enabling fluoroalkylation reactions. This study broadens the potential applications of molecular photoelectrocatalysis, highlighting its capacity to enable transformations that are difficult to accomplish through traditional electrochemical or photochemical approaches.

Photoinduced Late-Stage Radical Decarboxylative and Deoxygenative Coupling of Complex Carboxylic Acids and Their Derivatives

The simple and efficient conversion of carboxylic acids into structurally diverse organic molecules is highly desirable in chemical synthesis. This review covers recent developments in photocatalytic methodology for late-stage transformations of complex carboxylic acids and their derivatives enabled by radical decarboxylation and deoxygenation, highlighting some representative and significant contributions in this field. These advancements are categorized based on the reactivity patterns exhibited by the carboxylic acids. Several activation modes to generate alkyl or aryl radical intermediates during decarboxylation of carboxylic acids are presented, namely, single-electron transfer (SET) oxidation, ligand-to-metal charge transfer (LMCT), SET reduction, and energy transfer (EnT) processes. On the other hand, direct activation of C-O bonds in carboxylic acids mediated by phosphoranyl radicals has been discussed and illustrates their potential synthetic application for the synthesis of complex aldehydes, ketones and amides.

Enantioselective Decarboxylative Hydrogen-Atom Transfer Reaction

Direct enantioselective decarboxylative transformations of carboxylic acids have become powerful tools for constructing structurally and functionally diverse molecules. Herein, an unprecedented organocatalyzed protocol for enantioconvergent decarboxylative reduction was established by leveraging dual catalysis of photoredox-mediated radical generation and a thiol-catalyzed asymmetric hydrogen-atom transfer process. With this hydrodecarboxylation, a variety of chiral 3-substituted indolines were attained from the acids in moderate to excellent yields with high enantioselectivities.

Redox and Photochemical Reactivity of Cerium(IV) Carbonate and Carboxylate Complexes Supported by a Tripodal Oxygen Ligand

The protonolysis and redox reactivity of a Ce(IV) carbonate complex supported by the Kläui tripodal ligand [(η5-C5H5)Co{P(O)(OEt)2}3]- (LOEt-) have been studied. Whereas treatment of [Ce(LOEt)2(CO3)] (1) with RCO2H afforded [Ce(LOEt)2(RCO2)2] (R = Me (2), Ph (3), 2-NO2C6H3 (4)), the reaction of 1 with PhCH2CO2H resulted in formation of a mixture of Ce(IV) (5) and Ce(III) (6) carboxylate species. In benzene in the dark, 5 was slowly converted into 6 via Ce(IV)-O(carboxylate) homolysis. Recrystallization of a mixture of 5 and 6 from hexane led to isolation of yellow crystals of 6 that were identified as [Ce(LOEt)2(PhCH2CO2)]. Treatment of 1 with sulfamic acid, trifluoroacetamide, and trifluoromethanesulfonamide gave [Ce(LOEt)2(SO3NH)2] (7), [Ce(LOEt)2(CF3CONH)2] (8), and [Ce(LOEt)2(CF3SO2NH)2] (9), respectively. The crystal structures of 2, 4, and 6-8 have been determined. H atom transfer (HAT) of 2,6-di-tert-butylphenol and 9,10-dihydroanthracene (DHA) with 1 afforded 3,3',5,5'-tetra-tert-butyldiphenoquinone and anthracene, respectively. The oxidation of DHA with 1 under air yielded anthracene and anthraquinone. While 1 is stable in acetonitrile, it is readily reduced to a Ce(III) species in tetrahydrofuran. In air, 1 reacted with tetrahydrofuran to produce tetrahydrofuran hydroperoxide that can reduce the Ce(IV) carbonate rapidly. Upon irradiation with blue LED light, the Ce(IV)-LOEt carboxylate complexes underwent facile decarboxylation via Ce-O homolysis. 1 proved to be an efficient catalyst precursor for decarboxylative oxygenation of arylacetic acids. For example, irradiation of phenylacetic acid with blue LED light in the presence of 5 mol % of 1 under air afforded benzyl alcohol and benzaldehyde in 10 and 90% yield, respectively.

Enantioselective Synthesis of Axially Chiral Allylic Nitriles via Nickel-Catalyzed Desymmetric Cyanation of Biaryl Diallylic Alcohols

Axially chiral nitriles are common motifs in organic photoelectric materials, biological compounds, and agrochemicals. Unfortunately, the limited synthetic approaches to axially chiral nitriles have impeded their availability. Herein, we report the first nickel-catalyzed desymmetric allylic cyanation of biaryl allylic alcohols for the synthesis of axially chiral nitrile structures in high yields with excellent enantioselectivities (up to 90 % yield and >99 % ee). This process enables the synthesis of a diverse range of axially chiral allylic nitriles bearing β,γ-unsaturated alcohol moieties. Leveraging the allylic alcohol and cyano groups as versatile functionalization handles allow for further derivatization of these axially chiral frameworks. Density functional theory (DFT) calculations suggest that both steric and electronic interactions play crucial roles in determining the enantioselectivity of this transformation. Moreover, this mild and facile protocol is also applicable for gram-scale preparation of the chiral nitriles.

Modular access to saturated bioisosteres of anilines via photoelectrochemical decarboxylative C(sp3)-N coupling

In drug development, the substitution of benzene rings in aniline-based drug candidates with saturated bridged bicyclic ring systems often enhances pharmacokinetic properties while preserving biological activity. However, current efforts predominantly focuses on bicyclo[1.1.1]pentylamines, accessing analogs capable of mimicking ortho- and meta-substituted anilines remains challenging due to the lack of a versatile and modular synthetic methods. Herein, we present a modular approach to access a diverse array of saturated bioisosteres of anilines via photoelectrochemical-induced decarboxylative C(sp3)-N Coupling. The success of this reaction hinges on the merging the cooperative ligand-to-metal charge transfer (LMCT) with copper-catalyzed amination. Notably, this net-oxidative C(sp3)-N forming reaction operates under mild electrode potentials and proceeds through hydrogen evolution, eliminating the need for external chemical oxidants. Our research enables the facile decarboxylative amination of a set of sp3-rich small-ring cage carboxylic acids, thus offering a versatile bioisosteric replacement for ortho-, meta-, and para-substituted anilines and di(hetero)aryl amines.

Molecular Photoelectrocatalysis for Radical Reactions

ConspectusMolecular photoelectrocatalysis, which combines the merits of photocatalysis and organic electrosynthesis, including their green attributes and capacity to offer novel reactivity and selectivity, represents an emerging field in organic chemistry that addresses the growing demands for environmental sustainability and synthetic efficiency. This synergistic approach permits access to a wider range of redox potentials, facilitates redox transformations under gentler electrode potentials, and decreases the use of external harsh redox reagents. Despite these potential advantages, this area did not receive significant attention until 2019, when we and others reported the first examples of modern molecular photoelectrocatalysis. These studies showcased the immense synthetic potential of this hybrid strategy, which not only inherits the strengths of its parent fields but also unlocks unprecedented reactivity and selectivity, enabling challenging transformations under mild conditions while minimizing the reliance on external stoichiometric harsh oxidants or reductants.In this Account, we present our efforts to develop photoelectrocatalytic strategies that leverage homogeneous catalysts to facilitate diverse radical reactions. By integrating electrocatalysis with key photoinduced processes such as single electron transfer (SET), ligand-to-metal charge transfer (LMCT), and hydrogen atom transfer (HAT), we have established photoelectrocatalytic methods to transform substrates such as organotrifluoroborates, arenes, carboxylic acids, and alkanes into reactive radical intermediates. These intermediates subsequently engage in heteroarene C-H functionalization reactions. Importantly, under these photoelectrochemical conditions with homogeneous catalysts, reactive radical intermediates generated in the bulk solution readily participate in efficient radical reactions without undergoing further overoxidation into carbocations, a common challenge in conventional electrochemical systems.By further integration of photoelectrocatalysis with asymmetric catalysis, we have developed photoelectrochemical asymmetric catalysis (PEAC), which proves to be efficient in the enantioselective synthesis of chiral nitriles. This approach involves two relay catalytic cycles: the initial photoelectrocatalytic process engenders benzylic radicals from precursors such as alkyl arenes, benzylic carboxylic acids, and aryl alkenes, and these C-radicals are then subjected to enantioselective cyanation in a subsequent copper-electrocatalytic cycle.Within the realm of oxidative photoelectrochemical transformations, the anode serves as a crucial component for recycling or generating the photocatalyst, while the cathode promotes proton reduction. This dual functionality enables oxidative transformations via H2 evolution, eliminating the reliance on external chemical oxidants. Furthermore, the adaptability of electrochemical systems, achieved through precise manipulation of electric current or potential, ensures meticulous control over the generation and turnover of multiple catalytic species of diverse electrochemical properties. This unique tunability allows for exceptional control over the catalytic process. As a result, despite being a relatively nascent field, molecular photoelectrocatalysis has become instrumental in enabling numerous challenging transformations that were once difficult or required harsh conditions.

Recent advances in electrochemical copper catalysis for modern organic synthesis

In recent decades, organic electrosynthesis has emerged as a practical, sustainable, and efficient approach that facilitates valuable transformations in synthetic chemistry. Combining electrochemistry with transition-metal catalysis is a promising and rapidly growing methodology for effectively forming challenging C-C and C-heteroatom bonds in complex molecules in a sustainable manner. In this review, we summarize the recent advances in the combination of electrochemistry and copper catalysis for various organic transformations.

Electrochemical Halogenation of Naphthoquinones: A Modular and Sustainable Strategy Towards Trypanocidal Compounds

An eco-friendly electrochemical halogenation of 2-amino-1,4-naphthoquinones has been developed. The new mild and energy efficient methodology comprises sustainable features like oxidant free and double role of the halogen source as electrolyte, originating twenty-six amino-halogenated naphthoquinoidal derivatives in good yields under mild conditions. This novel methodology permitted access to new potent trypanocidal prototypes, where six compounds were more active than benznidazole, the current market drug used in the treatment of Chagas Disease.

Enantioselective Nickel-Electrocatalyzed Cross-Dehydrogenative α- and γ-Nitroalkylation

Asymmetric catalytic versions of electricity-driven processes hold immense potential for the sustainable preparation of chiral compounds. However, the involvement of anodic oxidative cross-dehydrogenative coupling events between two distinct nucleophiles makes it challenging for a chiral catalyst to regulate the stereochemistry of the products. Our current electrocatalytic strategy for enantioconvergent cross-dehydrogenative α- and γ-nitroalkylation via radical-based pathways produces an array of enantioenriched nitroesters without supplementary stoichiometric oxidants. Mechanistic investigations reveal that the nickel catalyst plays a key role in both the electrochemical activation of the substrates and the stereoselectivity-defining events, affording the electrochemically generated Lewis acid-bound α-carbonyl radicals to interact with in situ-generated nitronate anions in a stereoselective manner. This electrocatalytic approach enables transformations that are highly challenging under thermal conditions, such as umpolung reactivity with readily available substrates, all-carbon quaternary stereocenter creation, and the control of remote stereochemistry.

Decarboxylative Alkylation of Carboxylic Acids with Easily Oxidizable Functional Groups Catalyzed by an Imidazole-Coordinated Fe3 Cluster under Visible Light Irradiation

Decarboxylative alkylation of carboxylic acids with easily oxidizable functional groups such as phenol and indole functionalities was achieved using a catalytic amount of basic iron(III) acetate, Fe(OAc)2(OH), in the presence of benzimidazole under 427 nm LED irradiation. Kinetic analyses of this catalytic reaction revealed that the reaction rate is first-order in alkenes and is linearly correlated with the light intensity; the faster reaction rate for the benzimidazole-ligated species was consistent with the increased absorbance in the visible light region. Wide functional group tolerance for the easily oxidizable groups is ascribed to the weak oxidation ability of the in situ-generated oxo-bridged iron clusters compared with other iron(III) species.

Electrochemical Decarboxylation Coupling Reactions

Carboxylic acids are attractive synthetic feedstocks with stable, non-toxic, and inexpensive properties that can be easily obtained from natural sources or through synthesis. Carboxylic acids have long been considered environmentally friendly coupling agents in various organic transformations. In recent years, electrochemically mediated decarboxylation reactions of decarboxylic acids and their derivatives (NHPI) have emerged as effective new methods for constructing carbon-carbon or carbon-heterocarbon chemical bonds. Compared with transition metal and photochemistry-mediated catalytic reactions, which do not require the addition of oxidants and strong bases, electrochemically-mediated decarboxylative transformations are considered a sustainable strategy. In addition, various functional groups tolerate the electrochemical decarboxylation conversion strategy well. Here, we summarize the recent electrochemical decarboxylation reactions to better elucidate the advantages of electrochemical decarboxylation reactions.

Electrophotocatalysis for Organic Synthesis

Electrocatalysis and photocatalysis have been the focus of extensive research efforts in organic synthesis in recent decades, and these powerful strategies have provided a wealth of new methods to construct complex molecules. Despite these intense efforts, only recently has there been a significant focus on the combined use of these two modalities. Nevertheless, the past five years have witnessed rapidly growing interest in the area of electrophotocatalysis. This hybrid strategy capitalizes on the enormous benefits of using photons as reagents while also employing an electric potential as a convenient and tunable source or sink of electrons. Research on this topic has led to a number of methods for C-H functionalization, reductive cross-coupling, and olefin addition among others. This field has also seen the use of a broad range of catalyst types, including both metal and organocatalysts. Of particular note has been work with open-shell photocatalysts, which tend to have comparatively large redox potentials. Electrochemistry provides a convenient means to generate such species, making electrophotocatalysis particularly amenable to this intriguing class of redox catalyst. This review surveys methods in the area of electrophotocatalysis as applied to organic synthesis, organized broadly into oxidative, reductive, and redox neutral transformations.

Asymmetric paired oxidative and reductive catalysis enables enantioselective alkylarylation of olefins with C(sp3)-H bonds

Enantioselective transformations of hydrocarbons to three-dimensional chiral molecules remain a significant challenge in synthetic chemistry. This study uses asymmetric paired oxidative and reductive catalysis to promote the enantioselective alkylarylation of olefins through the functionalization of C(sp3)-H bonds in alkanes. This asymmetric photoelectrocatalytic approach enables the facile construction of a wide range of enantioenriched α-aryl carbonyls with excellent enantioselectivity (up to 96% ee) from readily accessible starting materials. Notably, aryl bromides, aryl iodides, and even aryl chlorides were compatible with the developed catalytic system. Mechanistic studies reveal that alkanes and electrophiles are simultaneously activated on the electrodes.

Trityl isocyanide as a general reagent for visible light mediated photoredox-catalyzed cyanations

A photoredox catalytic strategy has been developed to enable the functionalization of a variety of commercially available, structurally different radical precursors by the use of a bench-stable isonitrile as an efficient cyanating reagent. Specifically, a radical-based reaction has provided a mild and convenient procedure for the cyanation of primary, secondary and tertiary radicals derived from widely accessible sp3-hybridized carboxylic acids, alcohols and halides under visible light irradiation. The reaction tolerates a variety of functional groups and it represents a complementary method for the cyanation of structurally different scaffolds that show diverse native functionalities, expanding the scope of previously reported methodologies.

Desymmetrization-Addition Reaction of Cyclopropenes to Imines via Synergistic Photoredox and Cobalt Catalysis

Herein, we designed a reaction for the desymmetrization-addition of cyclopropenes to imines by leveraging the synergy between photoredox and asymmetric cobalt catalysis. This protocol facilitated the synthesis of a series of chiral functionalized cyclopropanes with high yield, enantioselectivity, and diastereoselectivity (44 examples, up to 93% yield and >99% ee). A possible reaction mechanism involving cyclopropene desymmetrization by Co-H species and imine addition by Co-alkyl species was proposed. This study provides a novel route to important chiral cyclopropanes and extends the frontier of asymmetric metallaphotoredox catalysis.

Electrophotochemical metal-catalyzed synthesis of alkylnitriles from simple aliphatic carboxylic acids

We report a practical and sustainable electrophotochemical metal-catalyzed protocol for decarboxylative cyanation of simple aliphatic carboxylic acids. This environmentally friendly method features easy availability of substrates, broad functional group compatibility, and directly converts a diverse range of aliphatic carboxylic acids including primary and tertiary alkyl acids into synthetically versatile alkylnitriles without using chemical oxidants or costly cyanating reagents under mild reaction conditions.

Electrophotocatalysis Versus Indirect Electrolysis: Electrochemical Selenocyclization of 3-Aza-1,5-dienes Facilitated by Energy Transfer, Direct Photolysis or N-Hydroxyphthalimide

Three hybrid electrochemical protocols, which involve the energy transfer, direct photolysis and N-hydroxyphthalimide catalyst, respectively, are presented for the selenylation/cyclization of the fragile substrates of 3-aza-1,5-dienes with diorganyl diselenides to afford 3-selenomethyl-4-pyrrolin-2-ones. The two electrophotocatalytic reactions and the indirect electrolysis one are both regioselective and external-oxidant- and transition-metal-free, and are associated with a broad substrate scope and high Se-economy, and all three methods are amenable to gram-scale syntheses, late-stage functionalizations, sunlight-induced experiments and all-solar-driven syntheses.

Photoelectrochemical Fe/Ni cocatalyzed C-C functionalization of alcohols

The simultaneous activation of reactants on the anode and cathode via paired electrocatalysis has not been extensively demonstrated. This report presents a paired oxidative and reductive catalysis based on earth-abundant iron/nickel cocatalyzed C-C functionalization of ubiquitous alcohols. A variety of alcohols (i.e., primary, secondary, tertiary, or unstrained cyclic alcohols) can be activated at very low oxidation potential of (~0.30 V vs. Ag/AgCl) via photoelectrocatalysis coupled with versatile electrophiles. This reactivity yields a wide range of structurally diverse molecules with broad functional group compatibility (more than 50 examples).

Electrochemical synthesis of peptide aldehydes via C‒N bond cleavage of cyclic amines

Peptide aldehydes are crucial biomolecules essential to various biological systems, driving a continuous demand for efficient synthesis methods. Herein, we develop a metal-free, facile, and biocompatible strategy for direct electrochemical synthesis of unnatural peptide aldehydes. This electro-oxidative approach enabled a step- and atom-economical ring-opening via C‒N bond cleavage, allowing for homoproline-specific peptide diversification and expansion of substrate scope to include amides, esters, and cyclic amines of various sizes. The remarkable efficacy of the electro-synthetic protocol set the stage for the efficient modification and assembly of linear and macrocyclic peptides using a concise synthetic sequence with racemization-free conditions. Moreover, the combination of experiments and density functional theory (DFT) calculations indicates that different N-acyl groups play a decisive role in the reaction activity.

Enantioselective Nickel-Electrocatalyzed Reductive Propargylic Carboxylation with CO2

The exploitation of carbon dioxide (CO2) as a sustainable, plentiful, and harmless C1 source for the catalytic synthesis of enantioenriched carboxylic acids has long been acknowledged as a pivotal task in synthetic chemistry. Herein, we present a current-driven nickel-catalyzed reductive carboxylation reaction with CO2 fixation, facilitating the formation of C(sp3)-C(sp2) bonds by circumventing the handling of moisture-sensitive organometallic reagents. This electroreductive protocol serves as a practical platform, paving the way for the synthesis of enantioenriched propargylic carboxylic acids (up to 98% enantiomeric excess) from racemic propargylic carbonates and CO2. The efficacy of this transformation is exemplified by its successful utilization in the asymmetric total synthesis of (S)-arundic acid, (R)-PIA, (S)-chizhine D, (S)-cochlearin G, and (S,S)-alexidine, thereby underscoring the potential of asymmetric electrosynthesis to achieve complex molecular architectures sustainably.

Nickel-Catalyzed Regio- and Enantioselective Migratory Hydrocyanation of Internal Alkenes: Expanding the Scope to α,ω-Diaryl Internal Alkenes

Metal-hydride-catalyzed migratory functionalization of alkenes witnessed extensive development in the past few years. However, the asymmetric version of this reaction has remained largely underdeveloped owing to the difficulty in simultaneous control of both regio- and stereoselectivity. In addition, exploring the wider alkene substrate scope to enable more synthetically valuable applications represents another challenge in this field. In this context, a nickel-catalyzed asymmetric hydrocyanation of internal alkenes involving a chain-walking process is demonstrated. The reaction exhibits excellent regio- and enantioselectivity, proceeds under mild reaction conditions, and delivers benzylic nitriles in high yields. Even α,ω-diaryl internal alkenes, which are known to be one of the most challenging substrates of this type, could be successfully converted to the desired products with good regio- and stereoselectivity by modifying the electronic and steric effects. Theoretical calculations suggest that the η3-benzyl coordination mode and the aryl substituent (3,5-(OMe)2C6H3) on the diphosphite ligand are both key factors in regulating regio- and enantioselectivity.

Recent advances in catalytic asymmetric synthesis

Asymmetric catalysis stands at the forefront of modern chemistry, serving as a cornerstone for the efficient creation of enantiopure chiral molecules characterized by their high selectivity. In this review, we delve into the realm of asymmetric catalytic reactions, which spans various methodologies, each contributing to the broader landscape of the enantioselective synthesis of chiral molecules. Transition metals play a central role as catalysts for a wide range of transformations with chiral ligands such as phosphines, N-heterocyclic carbenes (NHCs), etc., facilitating the formation of chiral C-C and C-X bonds, enabling precise control over stereochemistry. Enantioselective photocatalytic reactions leverage the power of light as a driving force for the synthesis of chiral molecules. Asymmetric electrocatalysis has emerged as a sustainable approach, being both atom-efficient and environmentally friendly, while offering a versatile toolkit for enantioselective reductions and oxidations. Biocatalysis relies on nature's most efficient catalysts, i.e., enzymes, to provide exquisite selectivity, as well as a high tolerance for diverse functional groups under mild conditions. Thus, enzymatic optical resolution, kinetic resolution and dynamic kinetic resolution have revolutionized the production of enantiopure compounds. Enantioselective organocatalysis uses metal-free organocatalysts, consisting of modular chiral phosphorus, sulfur and nitrogen components, facilitating remarkably efficient and diverse enantioselective transformations. Additionally, unlocking traditionally unreactive C-H bonds through selective functionalization has expanded the arsenal of catalytic asymmetric synthesis, enabling the efficient and atom-economical construction of enantiopure chiral molecules. Incorporating flow chemistry into asymmetric catalysis has been transformative, as continuous flow systems provide precise control over reaction conditions, enhancing the efficiency and facilitating optimization. Researchers are increasingly adopting hybrid approaches that combine multiple strategies synergistically to tackle complex synthetic challenges. This convergence holds great promise, propelling the field of asymmetric catalysis forward and facilitating the efficient construction of complex molecules in enantiopure form. As these methodologies evolve and complement one another, they push the boundaries of what can be accomplished in catalytic asymmetric synthesis, leading to the discovery of novel, highly selective transformations which may lead to groundbreaking applications across various industries.

Ligand Relay for Nickel-Catalyzed Decarbonylative Alkylation of Aroyl Chlorides

Transition metal-catalyzed direct decarboxylative transformations of aromatic carboxylic acids usually require high temperatures, which limit the substrate's scope, especially for late-stage applications. The development of the selective decarbonylative of carboxylic acid derivatives, especially the most fundamental aroyl chlorides, with stable and cheap electrophiles under mild conditions is highly desirable and meaningful, but remains challenging. Herein, a strategy of nickel-catalyzed decarbonylative alkylation of aroyl chlorides via phosphine/nitrogen ligand relay is reported. The simple phosphine ligand is found essential for the decarbonylation step, while the nitrogen ligand promotes the cross-electrophile coupling. Such a ligand relay system can effectively and orderly carry out the catalytic process at room temperature, utilizing easily available aroyl chlorides as an aryl electrophile for reductive alkylation. This discovery provides a new strategy for direct decarbonylative coupling, features operationally simple, mild conditions, and excellent functional group tolerance. The mild approach is applied to the late-stage methylation of various pharmaceuticals. Extensive experiments are carried out to provide insights into the reaction pathway and support the ligand relay process.

Asymmetric Paired Electrocatalysis: Enantioselective Olefin-Sulfonylimine Coupling

Asymmetric electrocatalysis offers exciting new strategies for the synthesis of chiral molecules through novel reaction pathways. However, simultaneous activation of reactants on both electrodes via asymmetric paired electrolysis, which is more energy efficient and economic than single half-electrode synthesis, remains a formidable challenge. Herein, an asymmetric olefin-sulfonylimine coupling via paired electrocatalysis is presented for the first time. In this protocol, Co-catalyzed hydrogen atom transfer on the anode and Ni-catalyzed sulfonylimine reduction on the cathode were seamlessly cross-coupled. The new catalytic system enables the formation of chiral amine products bearing a tetrasubstituted carbon stereocenter with a high enantioselectivity (up to 96% ee).

Electrophotocatalytic hydrogenation of imines and reductive functionalization of aryl halides

The open-shell catalytically active species, like radical cations or radical anions, generated by one-electron transfer of precatalysts are widely used in energy-consuming redox reactions, but their excited-state lifetimes are usually short. Here, a closed-shell thioxanthone-hydrogen anion species (3), which can be photochemically converted to a potent and long-lived reductant, is generated under electrochemical conditions, enabling the electrophotocatalytic hydrogenation. Notably, TfOH can regulate the redox potential of the active species in this system. In the presence of TfOH, precatalyst (1) reduction can occur at low potential, so that competitive H2 evolution can be inhibited, thus effectively promoting the hydrogenation of imines. In the absence of TfOH, the reducing ability of the system can reach a potency even comparable to that of Na0 or Li0, thereby allowing the hydrogenation, borylation, stannylation and (hetero)arylation of aryl halides to construct C-H, C-B, C-Sn, and C-C bonds.

Dual-Catalyzed Stereodivergent Electrooxidative Homocoupling of Benzoxazolyl Acetate

The development of a reliable strategy for stereodivergent radical reactions that allows convenient access to all stereoisomers of homocoupling adducts with multiple stereogenic centers remains an unmet goal in organic synthesis. Herein, we describe a dual-catalyzed electrooxidative C(sp3)-H/C(sp3)-H homocoupling with complete absolute and relative stereocontrol for the synthesis of molecules with contiguous quaternary stereocenters in a general and predictable manner. The stereodivergent electrooxidative homocoupling reaction is achieved by synergistically utilizing two distinct chiral catalysts that convert identical racemic substrates into inherently distinctive reactive chiral intermediates, dictate enantioselective radical addition, and allow access to the full complement of stereoisomeric products via simple catalyst permutation. The successful execution of the dual-electrocatalytic strategy programmed via electrooxidative activation provides a significant conceptual advantage and will serve as a useful foundation for further research into cooperative stereocontrolled radical transformations and diversity-oriented synthesis.

Accelerated Electrophotocatalytic C(sp3 )-H Heteroarylation Enabled by an Efficient Continuous-Flow Reactor

Electrophotocatalytic transformations are garnering attention in organic synthesis, particularly for accessing reactive intermediates under mild conditions. Moving these methodologies to continuous-flow systems, or flow ElectroPhotoCatalysis (f-EPC), showcases potential for scalable processes due to enhanced irradiation, increased electrode surface, and improved mixing of the reaction mixture. Traditional methods sequentially link photochemical and electrochemical reactions, using flow reactors connected in series, yet struggle to accommodate reactive transient species. In this study, we introduce a new flow reactor concept for electrophotocatalysis (EPC) that simultaneously utilizes photons and electrons. The reactor is designed with a transparent electrode and employs cost-effective materials. We used this technology to develop an efficient process for electrophotocatalytic heteroarylation of C(sp3 )-H bonds. Importantly, the same setup can also facilitate purely electrochemical and photochemical transformations. This reactor represents a significant advancement in electrophotocatalysis, providing a framework for its application in flow for complex synthetic transformations.

Comprehensive Comparisons between Directing and Alternating Current Electrolysis in Organic Synthesis

Organic electrosynthesis has consistently aroused significant interest within both academic and industrial spheres. Despite the considerable progress achieved in this field, the majority of electrochemical transformations have been conducted through the utilization of direct-current (DC) electricity. In contrast, the application of alternating current (AC), characterized by its polarity-alternating nature, remains in its infancy within the sphere of organic synthesis, primarily due to the absence of a comprehensive theoretical framework. This minireview offers an overview of recent advancements in AC-driven organic transformations and seeks to elucidate the differences between DC and AC electrolytic methodologies by probing into their underlying physical principles. These differences encompass the ability of AC to preclude the deposition of metal catalysts, the precision in modulating oxidation and reduction intensities, and the mitigation of mass transfer processes.

Selective C(sp3)-H arylation/alkylation of alkanes enabled by paired electrocatalysis

We report a combination of electrocatalysis and photoredox catalysis to perform selective C(sp3)-H arylation/alkylation of alkanes, in which a binary catalytic system based on earth-abundant iron and nickel is applied. Reaction selectivity between two-component C(sp3)-H arylation and three-component C(sp3)-H alkylation is tuned by modulating the applied current and light source. Importantly, an ultra-low anodic potential (~0.23 V vs. Ag/AgCl) is applied in this protocol, thus enabling compatibility with a variety of functional groups (>70 examples). The robustness of the method is further demonstrated on a preparative scale and applied to late-stage diversification of natural products and pharmaceutical derivatives.

A tutorial on asymmetric electrocatalysis

Electrochemistry has emerged as a powerful means to enable redox transformations in modern chemical synthesis. This tutorial review delves into the unique advantages of electrochemistry in the context of asymmetric catalysis. While electrochemistry has historically been used as a green and mild alternative for established enantioselective transformations, in recent years asymmetric electrocatalysis has been increasingly employed in the discovery of novel asymmetric methodologies based on reaction mechanisms unique to electrochemistry. This tutorial review first provides a brief tutorial introduction to electrosynthesis, then explores case studies on homogenous small molecule asymmetric electrocatalysis. Each case study serves to highlight a key advance in the field, starting with the historic electrification of known asymmetric transformations and culminating with modern methods relying on unique electrochemical mechanistic sequences. Finally, we highlight case studies in the emerging reasearch areas at the interface of asymmetric electrocatalysis with biocatalysis and heterogeneous catalysis.

Photoelectrochemical oxidative C(sp3)-H borylation of unactivated hydrocarbons

Organoboron compounds are of high significance in organic synthesis due to the unique versatility of boryl substituents to access further modifications. The high demand for the incorporation of boryl moieties into molecular structures has witnessed significant progress, particularly in the C(sp3)-H borylation of hydrocarbons. Taking advantage of special characteristics of photo/electrochemistry, we herein describe the development of an oxidative C(sp3)-H borylation reaction under metal- and oxidant-free conditions, enabled by photoelectrochemical strategy. The reaction exhibits broad substrate scope (>57 examples), and includes the use of simple alkanes, halides, silanes, ketones, esters and nitriles as viable substrates. Notably, unconventional regioselectivity of C(sp3)-H borylation is achieved, with the coupling site of C(sp3)-H borylation selectively located in the distal methyl group. Our method is operationally simple and easily scalable, and offers a feasible approach for the one-step synthesis of high-value organoboron building blocks from simple hydrocarbons, which would provide ample opportunities for drug discovery.

Electrochemical Late-Stage Functionalization

Late-stage functionalization (LSF) constitutes a powerful strategy for the assembly or diversification of novel molecular entities with improved physicochemical or biological activities. LSF can thus greatly accelerate the development of medicinally relevant compounds, crop protecting agents, and functional materials. Electrochemical molecular synthesis has emerged as an environmentally friendly platform for the transformation of organic compounds. Over the past decade, electrochemical late-stage functionalization (eLSF) has gained major momentum, which is summarized herein up to February 2023.

Parallel paired electrolysis-enabled asymmetric catalysis: simultaneous synthesis of aldehydes/aryl bromides and chiral alcohols

Metal-catalyzed asymmetric electro-reductive couplings have emerged as a powerful tool for organic synthesis, wherein a sacrificial anode is typically required. Herein, a parallel paired electrolysis (PPE)-enabled asymmetric catalysis has been developed, and the alcohols and ketones could be simultaneously converted to the corresponding aldehydes and chiral tertiary alcohols with high yields and enantioselectivity in an undivided cell. Additionally, this Ni-catalyzed asymmetric reductive coupling can well match the anodic oxidative C-H bond bromination of (hetero)arenes. This protocol opens an alternative avenue for organic synthesis.

Enantioselective catalytic radical decarbonylative azidation and cyanation of aldehydes

Empowered by the ubiquity of carbonyl functional groups in organic compounds, decarbonylative functionalization was prevalent in the construction of complex molecules. Under this context, asymmetric decarbonylative functionalization has emerged as an efficient pathway to accessing chiral motifs. However, ablation of enantiomeric control in a conventional 2e transition metal-catalyzed process was notable because of harsh conditions (high temperatures, etc.) that are usually required. To address this challenge and use readily accessible aldehyde directly, we report the asymmetric radical decarbonylative azidation and cyanation. Diverse aldehydes were directly used as alkyl radical precursor, engaging in the subsequent inner-sphere or outer-sphere ligand transfer where functional motifs (CN and N3) could be incorporated in excellent site- and enantioselectivity. Mild conditions, broad scope, excellent regioselectivity (driven by polarity-matching strategy), and enantioselectivity were shown for both transformations. This radical decarbonylative strategy using aldehydes as alkyl radical precursor has offered a powerful reaction manifold in asymmetric radical transformations to construct functional motifs regio- and stereoselectively.

Photoelectrochemical Asymmetric Catalysis Enables Enantioselective Heteroarylcyanation of Alkenes via C-H Functionalization

The asymmetric difunctionalization of alkenes, a method transforming readily accessible alkenes into enantioenriched chiral structures of high value, has long been a focal point of organic synthesis. Despite tremendous efforts in this domain, it remains a considerable challenge to devise enantioselective oxidative dicarbofunctionalization of alkenes, even though these transformations can utilize stable and unfunctionalized functional group donors. In this context, we report herein a photoelectrocatalytic method for the enantioselective heteroarylcyanation of aryl alkenes, which employs unfunctionalized heteroarenes through C-H functionalization. The photoelectrochemical asymmetric catalysis (PEAC) method combines photoredox catalysis and asymmetric electrocatalysis to facilitate the formation of two C-C bonds operating via hydrogen (H2) evolution and obviating the need for external chemical oxidants.

Photoredox catalysis harvesting multiple photon or electrochemical energies

Photoredox catalysis (PRC) is a cutting-edge frontier for single electron-transfer (SET) reactions, enabling the generation of reactive intermediates for both oxidative and reductive processes via photon activation of a catalyst. Although this represents a significant step towards chemoselective and, more generally, sustainable chemistry, its efficacy is limited by the energy of visible light photons. Nowadays, excellent alternative conditions are available to overcome these limitations, harvesting two different but correlated concepts: the use of multi-photon processes such as consecutive photoinduced electron transfer (conPET) and the combination of photo- and electrochemistry in synthetic photoelectrochemistry (PEC). Herein, we review the most recent contributions to these fields in both oxidative and reductive activations of organic functional groups. New opportunities for organic chemists are captured, such as selective reactions employing super-oxidants and super-reductants to engage unactivated chemical feedstocks, and scalability up to gram scales in continuous flow. This review provides comparisons between the two techniques (multi-photon photoredox catalysis and PEC) to help the reader to fully understand their similarities, differences and potential applications and to therefore choose which method is the most appropriate for a given reaction, scale and purpose of a project.

Copper-Catalyzed Asymmetric Cyanation of Propargylic Radicals via Direct Decarboxylation of Propargylic Carboxylic Acids

Chiral propargylic cyanides are often used as small-molecule feedstocks for the introduction of chiral centers into various valuable products and complex molecules. Here, we have developed a highly atom-economical strategy for the chiral copper complex-catalyzed synthesis of chiral propargylic cyanides. Propargylic radicals can be smoothly obtained by direct decarboxylation of the propargylic carboxylic acids without preactivation. The reactions show excellent selectivity and functional group compatibility. Gram-scale reaction and several conversion reactions from chiral propargylic cyanide have demonstrated the synthetic value of this strategy.

Chiral Discrimination of Nitrile Compounds Using a 19F-Labeled Palladium Probe

This study presents a ¹⁹F-labeled cyclopalladium probe for the rapid discrimination of chiral nitriles in pharmaceuticals, natural products, and agrochemicals. The probe binds reversibly to chiral nitriles, generating distinct ¹⁹F nuclear magnetic resonance signals for each enantiomer and enabling quick determination of enantiocomposition. The method allows for simultaneous detection of seven pairs of enantiomeric nitriles and application in assessing the enantiomeric excess of an asymmetric C-H cyanation reaction.

Copper-Catalyzed Enantioselective Decarboxylative Cyanation of Benzylic Acids Promoted by Hypervalent Iodine(III) Reagents

Copper-catalyzed asymmetric radical cyanation reactions have emerged as a powerful strategy for rapid construction of α-chiral nitriles. However, the directly decarboxylative cyanation reactions of common alkyl carboxylic acids remain largely elusive. Herein, we report a protocol for copper-catalyzed direct and enantioselective decarboxylative cyanation of benzylic acids. The in situ activation of acid substrates by a commercially inexpensive hypervalent iodine(III) reagent promoted the yield of the alkyl radicals under mild reaction conditions without prefunctionalization. The structurally diverse chiral alkyl nitriles were produced in good yields with high enantioselectivities. In addition, the chiral products can be readily converted to other useful chiral compounds via further transformations.

Photoinduced Cobalt-Catalyzed Desymmetrization of Dialdehydes to Access Axial Chirality

Enantioselective metallaphotoredox catalysis, which combines photoredox catalysis and asymmetric transition-metal catalysis, has become an effective approach to achieve stereoconvergence under mild conditions. Although many impressive synthetic approaches have been developed to access central chirality, the construction of axial chirality by metallaphotoredox catalysis still remains underexplored. Herein, we report two visible light-induced cobalt-catalyzed asymmetric reductive couplings of biaryl dialdehydes to synthesize axially chiral aldehydes (60 examples, up to 98% yield, >19:1 dr, and >99% ee). This protocol shows good functional group tolerance, broad substrate scope, and excellent diastereo- and enantioselectivity.

Photoinduced copper-catalyzed enantioselective coupling reactions

Copper-catalyzed enantioselective coupling has been widely investigated, which allows rapid construction of various chiral molecules. Despite important advances via polar and radical mechanisms, exploring general and practical strategies for the regio-, enantio- and diastereoselective assembly of stereogenic centers is of significant value but remains highly problematic. The integration of photocatalysis with asymmetric copper catalysis could provide appealing access to the development of new reaction pathways and structurally diverse chiral compounds, and extend the boundaries of radical chemistry. This review summarizes recent advances in photoinduced copper-catalyzed enantioselective coupling reactions, and discusses the mechanistic aspects.

Palladium-catalysed deaminative/decarboxylative cross-coupling of organoammonium salts with carboxylic acids

A palladium-catalysed carbon-carbon bond-forming reaction via deaminative/decarboxylative cross-coupling of organoammonium salts with carboxylic acids was developed. Under the reaction conditions, polyfluoroaromatic carboxylic acids, propiolic acids and α-cyano benzyl carboxylic acid reacted smoothly with benzyl ammonium salts to produce the corresponding carbon-carbon coupling products in good-to-excellent yields.

Cu-catalyzed enantioselective decarboxylative cyanation via the synergistic merger of photocatalysis and electrochemistry

The development of an efficient and straightforward method for decarboxylative coupling using common alkyl carboxylic acid is of great value. However, decarboxylative coupling with nucleophiles always needs stoichiometric chemical oxidants or substrate prefunctionalization. Herein, we report a protocol for Cu-catalyzed enantioselective decarboxylative cyanation via the merger of photocatalysis and electrochemistry. CeCl3 and Cu/BOX were used as co-catalysts to promote the decarboxylation and cyanation, and both catalysts were regenerated via anodic oxidation. This method establishes a proof of concept enantioselective transformation via photoelectrocatalysis. Studies by DFT calculations provided mechanistic insight on enantioselectivity control.

Electrophotochemical Metal-Catalyzed Enantioselective Decarboxylative Cyanation

In contrast to the rapid growth of electrophotocatalysis in recent years, enantioselective catalytic reactions powered by this unique methodology remain rare. In this work, we report an electrophotochemical metal-catalyzed protocol for direct asymmetric decarboxylative cyanation of aliphatic carboxylic acids. The synergistic merging of electrophotochemical cerium catalysis and asymmetric electrochemical copper catalysis permits mild reaction conditions for the formation and utilization of the key carbon centered radicals by combining the power of light and electrical energy. Electrophotochemical cerium catalysis enables radical decarboxylation to produce alkyl radicals, which could be effectively intercepted by asymmetric electrochemical copper catalysis for the construction of C-CN bonds in a highly stereoselective fashion. This environmentally benign method smoothly converts a diverse array of arylacetic acids into the corresponding alkyl nitriles in good yields and enantioselectivities without using chemical oxidants or pre-functionalization of the acid substrates and can be readily scaled up.