Ni-electrocatalytic Csp3-Csp3 doubly decarboxylative coupling

Hydrodeuteroalkylation of Unactivated Olefins Using Thianthrenium Salts

Isotopically labeled alkanes play a crucial role in organic and pharmaceutical chemistry. While some deuterated methylating agents are readily available, the limited accessibility of other deuteroalkyl reagents has hindered the synthesis of corresponding products. In this study, we introduce a nickel-catalyzed system that facilitates the synthesis of various deuterium-labeled alkanes through the hydrodeuteroalkylation of d2-labeled alkyl TT salts with unactivated alkenes. Diverging from traditional deuterated alkyl reagents, alkyl thianthrenium (TT) salts can effectively and selectively introduce deuterium at α position of alkyl chains using D2O as the deuterium source via a single-step pH-dependent hydrogen isotope exchange (HIE). Our method allows for high deuterium incorporation, and offers precise control over the site of deuterium insertion within an alkyl chain. This technique proves to be invaluable for the synthesis of various deuterium-labeled compounds, especially those of pharmaceutical relevance.

Solvent-dependent reaction mechanisms in the electrooxidative coupling of phenols: insights by operando Raman spectroelectrochemistry

The electrochemical oxidative phenol coupling reaction is a sustainable method for accessing biphenolic compounds. Using the dimerization of sesamol as a model reaction, insights into the reaction mechanism were gained via operando Raman spectroscopy. By varying the solvent and electrodes, different reaction mechanisms were identified and correlated with the respective product yields.

Electrochemical C-H Alkylation of Azauracils Using N-(Acyloxy)phthalimides

We present an electrochemical alkylation of azauracils using N-(acyloxy)phthalimides (NHPI esters) as readily available alkyl radical progenitors under metal- and additive-free conditions. Several azauracils are shown to undergo alkylation with an array of NHPI esters (1°, 2°, 3°, and sterically congested), providing the desired products in good to excellent yields. This operationally simple method is robust, scalable, and suitable for both batch and flow setups.

Deoxygenative radical cross-coupling of C(sp3)-O/C(sp3)-H bonds promoted by hydrogen-bond interaction

Building C(sp3)-rich architectures using simple and readily available starting materials will greatly advance modern drug discovery. C(sp3)-H and C(sp3)-O bonds are commonly used to strategically disassemble and construct bioactive compounds, respectively. However, the direct cross coupling of these two chemical bonds to form C(sp3)-C(sp3) bonds is rarely explored in existing literature. Conventional methods for forming C(sp3)-C(sp3) bonds via radical-radical coupling pathways often suffer from poor selectivity, severely limiting their practicality in synthetic applications. In this study, we present a single electron transfer (SET) strategy that enables the cleavage of amine α-C - H bonds and heterobenzylic C - O bonds to form C(sp3)-C(sp3) bonds. Preliminary mechanistic studies reveal a hydrogen bond interaction between substrates and phosphoric acid facilitates the cross-coupling of two radicals with high chemoselectivity. This methodology provides an effective approach to a variety of aza-heterocyclic unnatural amino acids and bioactive molecules.

Photoinduced Low-Valent Zirconium Catalysis for Cross-Electrophile Coupling of Ethers

Accessing versatile C(sp3)-C(sp3) bond through the cross-electrophile coupling of two distinct etheric C-O bonds is crucial in organic synthesis but remains barely explored. Herein, we report an innovative photoinduced low-valent zirconocene catalysis enabling the reductive coupling of ethers with high activity and cross-selectivity. Mechanistic investigation suggests that photoexcitation of low-valent zirconocene facilitates the C(sp3)-O bond scission of benzylic ethers, leading to the benzylic radicals intermediate via a single-electron reduction pathway. The subsequent recombination of this benzylic radical with the Zr center followed by carbomagnesiation generates benzylic Grignard reagents for downstream coupling with aliphatic ethers through an SN2-like mechanism. In application, a wide range of ethers readily in situ derived from aldehydes and ketones becomes feasible with high functional group compatibility as well as excellent cross-selectivity.

Nickel-Catalyzed Highly Selective Radical C-C Coupling from Carboxylic Acids with Photoredox Catalysis

Controlling the cross-coupling reaction between two different radicals is a long-standing challenge due to the process occurring statistically, which would lead to three products, including two homocoupling products and one cross-coupling product. Generally, the cross-coupling selectivity is achieved by the persistent radical effect (PRE) that requires the presence of a persistent radical and a transient radical, thus resulting in limited radical precursors. In this paper, a highly selective cross-coupling of alkyl radicals with acyl radicals to construct C(sp2)-C(sp3) bonds, or with alkyl radicals to construct C(sp3)-C(sp3) bonds have been achieved with the readily available carboxylic acids and their derivatives (NHPI ester) as coupling partners. The success originates from the use of tridentate ligand (2,2' : 6',2''-terpyridine) to enable radical cross-coupling process to Ni-mediated organometallic mechanism. This protocol offers a facile and flexible access to structurally diverse ketones (up to 90 % yield), and also a new solution for the challenging double decarboxylative C(sp3)-C(sp3) coupling. The broad utility and functional group tolerance are further illustrated by the late-stage functionalization of natural-occurring carboxylic acids and drugs.

Electrochemical Glycosylation via Halogen-Atom-Transfer for C-Glycoside Assembly

Glycosyl donor activation emerged as an enabling technology for anomeric functionalization, but aimed primarily at O-glycosylation. In contrast, we herein disclose mechanistically distinct electrochemical glycosyl bromide donor activations via halogen-atom transfer and anomeric C-glycosylation. The anomeric radical addition to alkenes led to C-alkyl glycoside synthesis under precious metal-free reaction conditions from readily available glycosyl bromides. The robustness of our e-XAT strategy was further mirrored by C-aryl and C-acyl glycosides assembly through nickela-electrocatalysis. Our approach provides an orthogonal strategy for glycosyl donor activation with expedient scope, hence representing a general method for direct C-glycosides assembly.

Electrochemical Nickel-Catalyzed Cross-Electrophile Coupling of Alkenyl Triflates with α-Chloroamides

Cross-electrophile coupling reactions of different electrophiles have been extensively studied but mainly limited to bromides and iodides. Here, we report an electrochemically induced nickel-catalyzed cross-electrophile coupling strategy between alkenyl triflates and α-chloroamides in an undivided cell under mild reaction conditions, affording the α-functionalized amide derivatives in good to excellent yields with broad substrate scopes and good functional group tolerance. The control experiments were conducted, and a plausible mechanism was proposed.

Oxidatively-induced C(sp3)-C(sp3) bond formation at a tucked-in iron(iii) complex

Carbon-carbon (C-C) bond formation is a cornerstone of synthetic chemistry, relying on routes such as transition-metal mediated cross-coupling for the introduction of new carbon-based functionality. For {[M] n+-C} (M = metal) structural units, studies that offer well-defined relationships between metal oxidation state, hydrocarbon strain, and {[M] n+-C} bond thermochemistry are thus informative, providing a means to reliably access new product classes. Here, we show that one-electron oxidation of the iron tucked-in complex [(η6-C5Me4[double bond, length as m-dash]CH2)Fe(dnppe)] (dnppe = 1,2-bis(di-n-propylphosphino)ethane) results in C(sp3)-C(sp3) bond formation giving unique {Fe2} dimers. Freeze-quenched CW X-band EPR spectroscopy allowed for spectroscopic identification of the reactive [(η6-C5Me4[double bond, length as m-dash]CH2)Fe(dnppe)]+ intermediate. Density functional theory (DFT) calculations reveal a primarily Fe-centered radical and a weak {[Fe]-C} bond (BDE[Fe]-C = 24.5 kcal mol-1, c.f. BDEC-C(ethane) = 90 kcal mol-1). For comparison, a structurally analogous Fe(iii) methyl complex was prepared, [Cp*Fe(dnppe)(CH3)]+ (Cp* = C5Me5 -), where C(sp3)-C(sp3) coupling was not observed, consistent with a larger calculated BDE[Fe]-C value of 47.8 kcal mol-1. These data are analogized to the simple hydrocarbons ethane and cyclopropane, where a strain-induced BDEC-C decrease of 33 kcal mol-1 is witnessed on cyclization.

Cost-Effective Carbon Quaternization with Redox-Active Esters and Olefins

Quaternary carbons are embedded in various natural products, pharmaceuticals, and organic materials. However, constructing this valuable motif is far from trivial. Conventional approaches mainly rely on classical polar disconnections and encounter bottlenecks concerning harsh conditions, functional group tolerance, regioselectivity, and step economy. In this context, Kawamata, Baran, Shenvi, and co-workers recently demonstrated that two feedstock chemicals, alkyl carboxylic acids and olefins, could be utilized to construct tetrasubstituted carbons in the presence of an inexpensive iron porphyrin catalyst and a suitable reductant combination through quaternization of the radical intermediates. The method enables access to various sterically encumbered quaternary carbons under mild and robust conditions. Taking a complete detour from conventional approaches, the present heteroselective radical-radical coupling simplifies the synthesis of quaternary carbon-containing molecules through an innovative and distinctive disconnection approach.

Single-Atom Iron Catalyst as an Advanced Redox Mediator for Anodic Oxidation of Organic Electrosynthesis

Homogeneous electrocatalysts can indirect oxidate the high overpotential substrates through single-electron transfer on the electrode surface, enabling efficient operation of organic electrosynthesis catalytic cycles. However, the problems of this chemistry still exist such as high dosage, difficult recovery, and low catalytic efficiency. Single-atom catalysts (SACs) exhibit high atom utilization and excellent catalytic activity, hold great promise in addressing the limitations of homogeneous catalysts. In view of this, we have employed Fe-SA@NC as an advanced redox mediator to try to change this situation. Fe-SA@NC was synthesized using an encapsulation-pyrolysis method, and it demonstrated remarkable performance as a redox mediator in a range of reported organic electrosynthesis reactions, and enabling the construction of various C-C/C-X bonds. Moreover, Fe-SA@NC demonstrated a great potential in exploring new synthetic method for organic electrosynthesis. We employed it to develop a new electro-oxidative ring-opening transformation of cyclopropyl amides. In this new reaction system, Fe-SA@NC showed good tolerance to drug molecules with complex structures, as well as enabling flow electrochemical syntheses and gram-scale transformations. This work highlights the great potential of SACs in organic electrosynthesis, thereby opening a new avenue in synthetic chemistry.

Synergistic use of photocatalysis and convergent paired electrolysis for nickel-catalyzed arylation of cyclic alcohols

The merging of transition metal catalysis with electrochemistry has become a powerful tool for organic synthesis because catalysts can govern the reactivity and selectivity. However, coupling catalysts with alkyl radical species generated by anodic oxidation remains challenging because of electrode passivation, dimerization, and overoxidation. In this study, we developed convergent paired electrolysis for the coupling of nickel catalysts with alkyl radicals derived from photoinduced ligand-to-metal charge-transfer of cyclic alcohols and iron catalysts, providing a practical method for site-specific and remote arylation of ketones. The synergistic use of photocatalysis with convergent paired electrolysis can provide alternative avenues for metal-catalyzed radical coupling reactions.

Palladium-Catalyzed Allylation of Endocyclic 1-Azaallyl Anions

Endocyclic 1-azaallyl anions engage allyl acetates in a palladium-catalyzed allylation followed by reduction to give unprotected 2-(hetero)aryl-3-allylpiperidines and 2-allyl-3-arylmorpholines, products not easily accessible by other means. The allyl group is then readily transformed into a variety of functional groups. Preliminary studies on the asymmetric variant of the reaction using an enantiomerically pure BI-DIME-type ligand provide the product with moderate enantioselectivity. Computational studies suggest that energy barriers of inner-sphere reductive elimination and outer-sphere nucleophilic substitution are almost the same, which makes both of them possible reaction pathways. In addition, the inner-sphere mechanism displays an enantiodiscriminating C-C bond forming step, while the outer-sphere mechanism is much less selective, which combined to give the asymmetric variant of the reaction moderate enantioselectivity.

Carbon quaternization of redox active esters and olefins by decarboxylative coupling

The synthesis of quaternary carbons often requires numerous steps and complex conditions or harsh reagents that act on heavily engineered substrates. This is largely a consequence of conventional polar-bond retrosynthetic disconnections that in turn require multiple functional group interconversions, redox manipulations, and protecting group chemistry. Here, we report a simple catalyst and reductant combination that converts two types of feedstock chemicals, carboxylic acids and olefins, into tetrasubstituted carbons through quaternization of radical intermediates. An iron porphyrin catalyst activates each substrate by electron transfer or hydrogen atom transfer, and then combines the fragments using a bimolecular homolytic substitution (SH2) reaction. This cross-coupling reduces the synthetic burden to procure numerous quaternary carbon---containing products from simple chemical feedstocks.

Oxidative Dehydroxycyclization of Catechols with o-Mercaptoanilines to Access 1-Hydroxyphenothiazines

The protocol of aerobic oxidative dehydroxycyclization installed in the synthesis of rarely studied 1-hydroxyphenothiazines from catechols and o-mercaptoanilines is presented. Utilizing a natural renewable low-toxicity gallic acid as an organocatalyst, this established transformation proceeded smoothly in an aqueous ethanol solution under mild conditions with good functional group compatibility and up to a 94% isolated yield. This protocol is also characterized by its operational simple workup involving only recrystallization, revealing its sustainability and synthetic practicability.

Paired electrocatalysis unlocks cross-dehydrogenative coupling of C(sp3)-H bonds using a pentacoordinated cobalt-salen catalyst

Cross-dehydrogenative coupling of C(sp3)-H bonds is an ideal approach for C(sp3)-C(sp3) bond construction. However, conventional approaches mainly rely on a single activation mode by either stoichiometric oxidants or electrochemical oxidation, which would lead to inferior selectivity in the reaction between similar C(sp3)-H bonds. Herein we describe our development of a paired electrocatalysis strategy to access an unconventional selectivity in the cross-dehydrogenative coupling of alcoholic α C(sp3)-H with allylic (or benzylic) C-H bonds, which combines hydrogen evolution reaction catalysis with hydride transfer catalysis. To maximize the synergistic effect of the catalyst combinations, a HER catalyst pentacoordinated Co-salen is disclosed. The catalyst displays a large redox-potential gap (1.98 V) and suitable redox potential. With the optimized catalyst combination, an electrochemical cross-dehydrogenative coupling protocol features unconventional chemoselectivity (C-C vs. C-O coupling), excellent functional group tolerance (84 examples), valuable byproduct (hydrogen), and high regio- and site-selectivity. A plausible reaction mechanism is also proposed to rationalize the experimental observations.

Electroreduction of unactivated alkenes using water as hydrogen source

Herein, we report an electroreduction of unactivated alkyl alkenes enabled by [Fe]-H, which is provided through the combination of anodic iron salts and the silane generated in situ via cathodic reduction, using H2O as an H-source. The catalytic amounts of Si-additive work as an H-carrier from H2O to generate a highly active silane species in situ under continuous electrochemical conditions. This approach shows a broad substrate scope and good functional group compatibility. In addition to hydrogenation, the use of D2O instead of H2O provides the desired deuterated products in good yields with excellent D-incorporation (up to >99%). Further late-stage hydrogenation of complex molecules and drug derivatives demonstrate potential application in the pharmaceutical industry. Mechanistic studies are performed and provide support for the proposed mechanistic pathway.

Alcohol-alcohol cross-coupling enabled by SH2 radical sorting

Alcohols represent a functional group class with unparalleled abundance and structural diversity. In an era of chemical synthesis that prioritizes reducing time to target and maximizing exploration of chemical space, harnessing these building blocks for carbon-carbon bond-forming reactions is a key goal in organic chemistry. In particular, leveraging a single activation mode to form a new C(sp3)-C(sp3) bond from two alcohol subunits would enable access to an extraordinary level of structural diversity. In this work, we report a nickel radical sorting-mediated cross-alcohol coupling wherein two alcohol fragments are deoxygenated and coupled in one reaction vessel, open to air.

Electrochemical Ni-Catalyzed Decarboxylative C(sp3 )-N Cross-Electrophile Coupling

A new electrochemical transformation is presented that enables chemists to couple simple alkyl carboxylic acid derivatives with an electrophilic amine reagent to construct C(sp3 )-N bond. The success of this reaction hinges on the merging of cooperative electrochemical reduction with nickel catalysis. The chemistry exhibits a high degree of practicality, showcasing its wide applicability with 1°, 2°, 3° carboxylic acids and remarkable compatibility with diverse functional groups, even in the realm of late-stage functionalization. Furthermore, extensive mechanistic studies have unveiled the engagement of alkyl radicals and iminyl radicals; and elucidated the multifaceted roles played by i Pr2 O, Ni catalyst, and electricity.

Iron-Catalyzed Csp2-Csp3 Cross-Coupling via Double Decarboxylation: One Step Synthesis of Remote Polar Alkenes

Herein, we report an efficient photoinduced iron-catalyzed strategy for cross-couplings of alkyl carboxylic and acrylic acids, which provides a powerful tool for the synthesis of a variety of alkenes with polar functional groups. This novel synthetic methodology can also be applied to the preparation of ketones by using α-keto acids. Mechanistic experiments revealed preliminary mechanistic details. Diverse functionalization could be achieved, which may help streamline the synthesis of complex analogues for drug discovery.

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.

Metal-free photocatalytic cross-electrophile coupling enables C1 homologation and alkylation of carboxylic acids with aldehydes

In contemporary drug discovery, enhancing the sp3-hybridized character of molecular structures is paramount, necessitating innovative synthetic methods. Herein, we introduce a deoxygenative cross-electrophile coupling technique that pairs easily accessible carboxylic acid-derived redox-active esters with aldehyde sulfonyl hydrazones, employing Eosin Y as an organophotocatalyst under visible light irradiation. This approach serves as a versatile, metal-free C(sp3)-C(sp3) cross-coupling platform. We demonstrate its synthetic value as a safer, broadly applicable C1 homologation of carboxylic acids, offering an alternative to the traditional Arndt-Eistert reaction. Additionally, our method provides direct access to cyclic and acyclic β-arylethylamines using diverse aldehyde-derived sulfonyl hydrazones. Notably, the methodology proves to be compatible with the late-stage functionalization of peptides on solid-phase, streamlining the modification of intricate peptides without the need for exhaustive de-novo synthesis.

Switchable Decarboxylation by Energy- or Electron-Transfer Photocatalysis

Kolbe dimerization and Hofer-Moest reactions are well-investigated carboxylic acid transformations, wherein new carbon-carbon and carbon-heteroatom bonds are constructed via electrochemical decarboxylation. These transformations can be switched by choosing an electrode that allows control of the reactive intermediate, such as carbon radical or carbocation. However, the requirement of a high current density diminishes the functional group compatibility with these electrochemical reactions. Here, we demonstrate the photocatalytic decarboxylative transformation of activated carboxylic acids in a switchable and functional group-compatible manner. We discovered that switching between Kolbe-type or Hofer-Moest-type reactions can be accomplished with suitable photocatalysts by controlling the reaction pathways: energy transfer (EnT) and single-electron transfer (SET). The EnT pathway promoted by an organo-photocatalyst yielded 1,2-diarylethane from arylacetic acids, whereas the ruthenium photoredox catalyst allows the construction of an ester scaffold with two arylmethyl moieties via the SET pathway. The resulting radical intermediates were coupled to olefins to realize multicomponent reactions. Consequently, four different products were selectively obtained from a simple carboxylic acid. This discovery offers new opportunities for selectively synthesizing multiple products via switchable reactions using identical substrates with minimal cost and effort.

Single-Atom Manganese-Catalyzed Oxygen Evolution Drives the Electrochemical Oxidation of Silane to Silanol

The oxygen evolution reaction (OER), characterized by a four-electron transfer kinetic process, represents a significant bottleneck in improving the efficiency of hydrogen production from water electrolysis. Consequently, extensive research efforts have been directed towards identifying single-atom electrocatalysts with exceptional OER performance. Despite the comprehensive understanding of the OER mechanism, its application to other valuable synthetic reactions has been limited. Herein, we leverage the MOOH intermediate, a key species in the Mn-N-C single-atom catalyst (Mn-SA@NC), which can be cyclically delivered in the OER. We exploit this intermediate' s capability to facilitate electrophilic transfer with silane, enabling efficient silane oxidation under electrochemical conditions. The SAC electrocatalytic system exhibits remarkable performance with catalyst loadings as low as 600 ppm and an exceptional turnover number of 9132. Furthermore, the catalytic method demonstrates stability under a 10 mmol flow chemistry setup. By serving as an OER electrocatalyst, the Mn-SA@NC drives the entire reaction, establishing a practical Mn SAC-catalyzed organic electrosynthesis system. This synthesis approach not only presents a promising avenue for the utilization of electrocatalytic OER but also highlights the potential of SACs as an attractive platform for organic electrosynthesis investigations.

Coligands Controlled Reactivities of Ruthenium(II) Precursors: Antiferromagnetically Coupled Ruthenium(III)-Phenoxyl versus Ruthenium(II)-Phenoxyl Forms

The study disclosed that the reactivities of [RuII (PPh3)3Cl2] and [RuII(PPh3)3(CO)(H)Cl] precursors toward a trimethoxyarylimino-phenol derivative are sensibly different. The former promotes methoxy demethylation reaction affording a [Phenolato-RuIII-Phenolato] unit, while the latter containing π-acidic CO and hydride as coligands leads to C-H activation reaction, generating a [Phenolato-RuII-Aryl] unit. Notably, the oxidized analogues of these two forms produce antiferromagnetically coupled [RuIII-phenoxyl] and paramagnetic [RuII-phenoxyl] forms, which exhibit diverse reactivities. Surprisingly, the magnetically coupled [RuIII-phenoxyl] form obtained from [Phenolato-RuIII-Phenolato] motif leads to coligand, PPh3 oxidation and undergoes dimerization, making a Ru-Ru bond (2.599(2) Å), while the [RuII-phenoxyl] form obtained from [Phenolato-RuII-Aryl] motif leads to C-C coupling and H abstraction reactions. The coupling reaction affords a 4,4'-dibenzosemiquinonate anion radical complex, but the H-abstraction of the phenoxyl form gives a [RuII-Phenol] complex. For comparison, [RuII(IQR 0)] and [RuII(ISQR·-)] complexes were also isolated, where IQR 0 and ISQR·- are p-R-o-iminobenzoquinone and p-R-o-iminobenzosemiquinonate anion radicals. However, they fail to promote any bond-formation reaction. The molecular and electronic structures of the ruthenium (II/III) complexes were confirmed by single-crystal X-ray crystallography, EPR spectroscopy, and DFT calculations.

Photoinduced Direct Electron Transfer between Quinoxalin-2(1H)-ones and Alkyl Carboxylic Acids for C-H Alkylation

The progress of efficient and sustainable approaches for decarboxylative coupling reactions is synthetically appealing due to the structural diversity, lack of toxicity, and widespread commercial accessibility of carboxylic acids. However, the decarboxylation reaction still encounters challenges related to the utilization of oxidants, catalysts, and prefunctionalization conditions. We report herein a mild method that facilitates direct electron transfer between alkyl carboxylic acids and excited-state substrates for C-H alkylation of quinoxalin-2(1H)-ones without the involvement of any catalyst or additive.

Divergent Synthesis of 1,2,3,4-Tetrasubstituted Cyclobutenes from a Common Scaffold: Enantioselective Desymmetrization by Dual-Catalyzed Photoredox Cross-Coupling

Four-membered carbocycles are important structural motifs found in several natural products and drugs. Amongst those, cyclobutenes are attractive intermediates because the residual olefin can be manipulated selectively into various saturated and unsaturated analogs. Few methods exist to access chiral tri- and tetra-C-substituted cyclobutenes and they are generally limited in terms of diversification. Herein, a divergent synthetic strategy was developed where a single optically enriched scaffold is diversified into a variety of derivatives with different substitution patterns. To this end, the enantioselective desymmetrization of prochiral 1,2-dibromocyclobutene imides was enabled by a dual Ir/Ni-catalyzed photoredox C(sp2 )-C(sp3 ) cross-coupling with an alkyltrifluoroborate salt to install a convertible carbon fragment in good yields and >90 % enantiomeric excess. Exceptional mono-coupling selectivity is observed and the resulting chiral bromocyclobutene serves as a common scaffold that can be transformed in a divergent manner into several valuable 1,2,3,4-tetra-C-substituted cyclobutane products while maintaining optical purity.

Enabling Al sacrificial anodes in tetrahydrofuran electrolytes for reductive electrosynthesis

Al0 is widely used as a sacrificial anode in organic electrosynthesis. However, there remains a notable knowledge gap in the understanding of Al anode interface chemistry under electrolysis conditions. We hypothesize that Al interfacial chemistry plays a pivotal role in the discernible bias observed in solvent selections for reductive electrosynthesis. The majority of existing methodologies that employ an Al sacrificial anode use N,N-dimethylformamide (DMF) as the preferred solvent, with only isolated examples of ethereal solvents such as tetrahydrofuran (THF). Given the crucial role of the solvent in determining the efficiency and selectivity of an organic reaction, limitations on solvent choice could significantly hinder substrate reactivity and impede the desired transformations. In this study, we aim to understand the Al metal interfaces and manipulate them to improve the performance of an Al sacrificial anode in THF-based electrolytes. We have discovered that the presence of halide ions (Cl-, Br-, I-) in the electrolyte is crucial for efficient Al stripping. By incorporating halide additive, we achieve bulk Al stripping in THF-based electrolytes and successfully improve the cell potentials of electrochemically driven reductive methodologies. This study will encourage the use of ethereal solvents in systems using Al sacrificial anodes and guide future endeavors in optimizing electrolytes for reductive electrosynthesis.

Electroreductive Cross-Electrophile Coupling (eXEC) Reactions

Electrochemistry utilizes electrons as a potent, controllable, and traceless alternative to chemical oxidants or reductants, and typically offers a more sustainable option for achieving selective organic synthesis. Recently, the merger of electrochemistry with readily available electrophiles has been recognized as a viable and increasingly popular methodology for efficiently constructing challenging C-C and C-heteroatom bonds in a sustainable manner for complex organic molecules. In this mini-review, we have systematically summarized the most recent advances in electroreductive cross-electrophile coupling (eXEC) reactions during the last decade. Our focus has been on readily available electrophiles, including aryl and alkyl organic (pseudo)halides, as well as small molecules such as CO2 , SO2 , and D2 O.

Organo-Mediator Enabled Electrochemical Deuteration of Styrenes

Despite widespread use of the deuterium isotope effect, selective deuterium labeling of chemical molecules remains a major challenge. Herein, a facile and general electrochemically driven, organic mediator enabled deuteration of styrenes with deuterium oxide (D2 O) as the economical deuterium source was reported. Importantly, this transformation could be suitable for various electron rich styrenes mediated by triphenylphosphine (TPP). The reaction proceeded under mild conditions without transition-metal catalysts, affording the desired products in good yields with excellent D-incorporation (D-inc, up to >99 %). Mechanistic investigations by means of isotope labeling experiments and cyclic voltammetry tests provided sufficient support for this transformation. Notably, this method proved to be a powerful tool for late-stage deuteration of biorelevant compounds.

Transition-Metal-Free Electrochemical Selenylative Cyclization of Alkynyl Phosphonates

Unprecedented regioselective electrochemical tandem selenation/cyclization of alkynyl phosphonates with diselenide is described here. These obtained selenoether products can be chemo-selectively converted into halogen-functionalized cyclic enol phosphonates under our electrochemical conditions. These protocols provide straightforward access to valuable cyclic enol phosphonate or phosphaisocoumarins under the electrochemical and transition-metal-free conditions. The robustness of these transformations was illustrated by their compatibility with various complex natural products and bioactive molecules. The selenoether and halogen functional groups allow the further diversification of the phosphorus heterocycles thus obtained.

Electrochemical Decarboxylative Elimination of Carboxylic Acids to Alkenes

An electrochemical strategy for the decarboxylative elimination of carboxylic acids to alkenes at room temperature has been developed. This mild and oxidant-free method provides a green alternative to traditional thermal decarboxylation reactions. Structurally diverse aliphatic carboxylic acids, including biologically active drugs, underwent smooth conversion to the corresponding alkenes in good to excellent yields.

Complex molecule synthesis by electrocatalytic decarboxylative cross-coupling

Modern retrosynthetic analysis in organic chemistry is based on the principle of polar relationships between functional groups to guide the design of synthetic routes1. This method, termed polar retrosynthetic analysis, assigns partial positive (electrophilic) or negative (nucleophilic) charges to constituent functional groups in complex molecules followed by disconnecting bonds between opposing charges2-4. Although this approach forms the basis of undergraduate curriculum in organic chemistry5 and strategic applications of most synthetic methods6, the implementation often requires a long list of ancillary considerations to mitigate chemoselectivity and oxidation state issues involving protecting groups and precise reaction choreography3,4,7. Here we report a radical-based Ni/Ag-electrocatalytic cross-coupling of substituted carboxylic acids, thereby enabling an intuitive and modular approach to accessing complex molecular architectures. This new method relies on a key silver additive that forms an active Ag nanoparticle-coated electrode surface8,9 in situ along with carefully chosen ligands that modulate the reactivity of Ni. Through judicious choice of conditions and ligands, the cross-couplings can be rendered highly diastereoselective. To demonstrate the simplifying power of these reactions, concise syntheses of 14 natural products and two medicinally relevant molecules were completed.

Electrochemical NiH-Catalyzed C(sp3 )-C(sp3 ) Coupling of Alkyl Halides and Alkyl Alkenes

Herein, an electrochemically driven NiH-catalyzed reductive coupling of alkyl halides and alkyl alkenes for the construction of Csp3 -Csp3 bonds is firstly reported. Notably, alkyl halides serve dual function as coupling substrates and as hydrogen sources to generate NiH species under electrochemical conditions. The tunable nature of this reaction is realized by introducing an intramolecular coordinating group to the substrate, where the product can be easily adjusted to give the desired branched products. The method proceeds under mild conditions, exhibits a broad substrate scope, and affords moderate to excellent yields with over 70 examples, including late-stage modification of natural products and drug derivatives. Mechanistic insights offer evidence for an electrochemically driven coupling process. The sp3 -carbon-halogen bonds can be activated through single electron transfer (SET) by the nickel catalyst in its low valence state, generated by cathodic reduction, and the generation of NiH species from alkyl halides is pivotal to this transformation.

A Paradigm Shift in Catalysis: Electro- and Photomediated Nickel-Catalyzed Cross-Coupling Reactions

ConspectusTransition-metal catalyzed cross-coupling reactions are fundamental reactions in organic chemistry, facilitating strategic bond formations for accessing natural products, organic materials, agrochemicals, and pharmaceuticals. Redox chemistry enables access to elusive cross-coupling mechanisms through single-electron processes as an alternative to classical two-electron strategies predominated by palladium catalysis. The seminal reports of Baran, MacMillan, Doyle, Molander, Weix, Lin, Fu, Reisman, and others in merging redox perturbation (photochemical, electrochemical, and purely chemical) with catalysis are pivotal to the current resurgence and mechanistic understanding of first-row transition metal-based catalysis. The hallmark of this redox platform is the systematic modulation of transition-metal oxidation states by a photoredox catalyst or at a heterogeneous electrode surface. Electrocatalysis and photocatalysis enhance transition metal catalysis' capacity for bond formation through electron- or energy-transfer processes that promote otherwise challenging elementary steps or elusive mechanisms. Cross-coupling conditions promoted by electrocatalysis and photocatalysis are mild, and bond formation proceeds with exceptionally high chemoselectivity and wide functional group tolerance. The interfacing of abundant first-row transition-metal catalysis with electrocatalysis and photocatalysis has brought about a paradigm shift in cross-coupling technology as practitioners are quickly applying these tools in synthesizing fine chemicals and pharmaceutically relevant motifs. In particular, the merger of Ni catalysis with electro- and photochemistry ushered in a new era for carbon-carbon and carbon-heteroatom cross-couplings with expanded generality compared to their thermally driven counterparts. Over the past decade, we have developed enabling photo- and electrochemical methods throughout our combined research experience in industry (BMS, AstraZeneca) and academia (Professor Baran, Scripps Research) in cross-disciplinary collaborative environments. In this Account, we will outline recent progress from our past and present laboratories in photo- and electrochemically mediated Ni-catalyzed cross-couplings. By highlighting these cross-coupling methodologies, we will also compare mechanistic features of both electro- and photochemical strategies for forging C(sp2)-C(sp3), C(sp3)-C(sp3), C-O, C-N, and C-S bonds. Through these side-by-side comparisons, we hope to demystify the subtle differences between the two complementary tools to enact redox control over transition metal catalysis. Finally, building off the collective experience of ourselves and the rest of the community, we propose a tactical user guide to photo- and electrochemically driven cross-coupling reactions to aid the practitioner in rapidly applying such tools in their synthetic designs.

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.

Comproportionation and disproportionation in nickel and copper complexes

Disproportionation and comproportionation reactions have become increasingly important electron transfer events in organometallic chemistry and catalysis. The renewed interest in these reactions is in part attributed to the improved understanding of first-row metals and their ability to occupy odd and even oxidation states. Disproportionation and comproportionation reactions enable metal complexes to shuttle between various oxidation states, a matter of utmost relevance for controlling the speciation and catalytic turnover. In addition, these reactions have a direct impact in the thermodynamic and kinetic stability of the corresponding metal complexes. This review covers the relevance and impact of these processes in electron transfer reactions and provides valuable information about their non-negligible influence in Ni- and Cu-catalysed transformations.

Low Pressure Carbonylation of Benzyl Carbonates and Carbamates for Applications in 13 C Isotope Labeling and Catalytic CO2 Reduction

Herein, we report a methodology to access isotopically labeled esters and amides from carbonates and carbamates employing an oxygen deletion strategy. This methodology utilizes a decarboxylative carbonylation approach for isotope labeling with near stoichiometric, ex situ generated 12 C, or 13 C carbon monoxide. This reaction is characterized by its broad scope, functional group tolerance, and high yields, which is showcased with the synthesis of structurally complex molecules. A complementary method that operates by the catalytic in situ generation of CO via the reduction of CO2 liberated during decarboxylation has also been developed as a proof-of-concept approach that CO2 -derived compounds can be converted to CO-containing frameworks. Mechanistic studies provide insight into the catalytic steps which highlight the impact of ligand choice to overcome challenges associated with low-pressure carbonylation methodologies, along with rational for the development of future methodologies.

2,6-Bis(pyrazol-1-yl)pyridine (1-bpp) as a General Ligand for the Negishi Alkylation of Alkylpyridinium Salts

A Ni/1-bpp catalyst was demonstrated to be effective in the Negishi alkylation with multiple classes of alkylpyridinium salts, including α-primary and α-secondary. These conditions are also effective for benzylic pyridinium salts, demonstrating the successful Negishi alkylation of benzylic pyridinium salts for the first time. Further, 14 derivatives of 1-bpp were prepared with a variety of steric and electronic properties to study how these changes impact the success of the Negishi alkylation.

Deep Electroreductive Chemistry: Harnessing Carbon- and Silicon-based Reactive Intermediates in Organic Synthesis

This Viewpoint outlines our recent contribution in electroreductive synthesis. Specifically, we leveraged deeply reducing potentials provided by electrochemistry to generate radical and anionic intermediates from readily available alkyl halides and chlorosilanes. Harnessing the distinct reactivities of radicals and anions, we have achieved several challenging transformations to construct C-C, C-Si, and Si-Si bonds. We highlight the mechanistic design principle that underpinned the development of each transformation and provide a view forward on future opportunities in growing area of reductive electrosynthesis.

Electrochemically Generated Carbanions Enable Isomerizing Allylation and Allenylation of Aldehydes with Alkenes and Alkynes

The direct coupling of aldehydes with petrochemical feedstock alkenes and alkynes would represent a practical and streamlined approach for allylation and allenylation chemistry. However, conventional approaches commonly require preactivated substrates or strong bases to generate allylic or propargylic carbanions and only afford branched allylation or propargylation products. Developing a mild and selective approach to access synthetically useful linear allylation and allenylation products is highly desirable, albeit with formidable challenges. We report a strategy using hydrogen evolution reaction (HER) to generate a carbanion from weakly acidic sp³ C-H bonds (pK_a ∼ 35-40) under mild reaction conditions, obviating the use of strong bases, Schlenk techniques, and multistep procedures. The cathodically generated carbanion reverses the typical reaction selectivity to afford unconventional isomerizing allylation and allenylation products (125 examples). The generation of carbanions was monitored and identified by in situ ultraviolet-visible (UV-vis) spectroelectrochemistry. Furthermore, we extended this protocol to the generation of other carbanions and their application in coupling reactions between alcohols with carbanions. The appealing features of this approach include mild reaction conditions, excellent functional group tolerance, unconventional chemo- and regioselectivity, and the diverse utility of products, which includes offering direct access to diene luminophores and bioactive scaffolds. We also performed cyclic voltammetry, control experiments, and density functional theory (DFT) calculations to rationalize the observed reaction selectivity and mechanism.

Bismuth radical catalysis in the activation and coupling of redox-active electrophiles

Radical cross-coupling reactions represent a revolutionary tool to make C(sp³)-C and C(sp³)-heteroatom bonds by means of transition metals and photoredox or electrochemical approaches. However, the use of main-group elements to harness this type of reactivity has been little explored. Here we show how a low-valency bismuth complex is able to undergo one-electron oxidative addition with redox-active alkyl-radical precursors, mimicking the behaviour of first-row transition metals. This reactivity paradigm for bismuth gives rise to well-defined oxidative addition complexes, which could be fully characterized in solution and in the solid state. The resulting Bi(III)-C(sp³) intermediates display divergent reactivity patterns depending on the α-substituents of the alkyl fragment. Mechanistic investigations of this reactivity led to the development of a bismuth-catalysed C(sp³)-N cross-coupling reaction that operates under mild conditions and accommodates synthetically relevant NH-heterocycles as coupling partners.

Ni-Electrocatalytic Enantioselective Doubly Decarboxylative C(sp3)-C(sp3) Cross Coupling

The first examples of enantioselective doubly decarboxylative cross coupling are disclosed. Malonate half amides are smoothly coupled to a variety of primary carboxylic acids after formation of the corresponding redox-active esters under Ni-electrocatalytic conditions using a new chiral ligand based on PyBox, resulting in amides with α-alkylated stereocenters. The scope of the reaction is broad, tolerating numerous functional groups, and uniformly proceeds with high ee. Finally, the potential utility of this enantioselective radical-radical reductive cross coupling to simplify synthesis is demonstrated with numerous case studies.

Ni-Catalyzed Electro-Reductive Cross-Electrophile Couplings of Alkyl Amine-Derived Radical Precursors with Aryl Iodides

In recent years, the "Escape-from-Flatland" trend has prompted the synthetic community to develop a set of cross-coupling strategies to introduce sp³-carbon-based fragments in organic compounds. This study presents a novel nickel-catalyzed electrochemical methodology for reductive cross-electrophile coupling. The method enables C(sp²)-C(sp³) linkages using inexpensive amine-derived radical precursors and aryl iodides. The use of electrochemistry as a power source reduces waste and avoids chemical reductants, making this approach a more sustainable alternative to traditional cross-coupling methods.

CO2-mediated organocatalytic chlorine evolution under industrial conditions

During the chlor-alkali process, in operation since the nineteenth century, electrolysis of sodium chloride solutions generates chlorine and sodium hydroxide that are both important for chemical manufacturing1-4. As the process is very energy intensive, with 4% of globally produced electricity (about 150 TWh) going to the chlor-alkali industry5-8, even modest efficiency improvements can deliver substantial cost and energy savings. A particular focus in this regard is the demanding chlorine evolution reaction, for which the state-of-the-art electrocatalyst is still the dimensionally stable anode developed decades ago9-11. New catalysts for the chlorine evolution reaction have been reported12,13, but they still mainly consist of noble metal14-18. Here we show that an organocatalyst with an amide functional group enables the chlorine evolution reaction; and that in the presence of CO2, it achieves a current density of 10 kA m-2 and a selectivity of 99.6% at an overpotential of only 89 mV and thus rivals the dimensionally stable anode. We find that reversible binding of CO2 to the amide nitrogen facilitates formation of a radical species that plays a critical role in Cl2 generation, and that might also prove useful in the context of Cl- batteries and organic synthesis19-21. Although organocatalysts are typically not considered promising for demanding electrochemical applications, this work demonstrates their broader potential and the opportunities they offer for developing industrially relevant new processes and exploring new electrochemical mechanisms.

Room Temperature Construction of Vicinal Amino Alcohols via Electroreductive Cross-Coupling of N-Heteroarenes and Carbonyls

Despite the widespread applications of α-hydroxyalkyl cyclic amines, direct and diverse access to such a class of unique vicinal amino alcohols still remains, to date, a challenge. Here, through a strategy of electroreductive α-hydroxyalkylation of inactive N-heteroarenes with ketones or electron-rich arylaldehydes, we describe a room temperature approach for the direct construction of α-hydroxyalkyl cyclic amines, which features a broad substrate scope, operational simplicity, high chemoselectivity, and no need for pressurized H₂ gas and transition metal catalysts. The zinc ion generated from anode oxidation plays a crucial role in the activation of both reactants by decreasing their reduction potentials. The strategy of electroreduction in combination with substrate activation by Lewis acids in this work is anticipated to develop more useful transformations.

Overcoming the limitations of Kolbe coupling with waveform-controlled electrosynthesis

The Kolbe reaction forms carbon-carbon bonds through electrochemical decarboxylative coupling. Despite more than a century of study, the reaction has seen limited applications owing to extremely poor chemoselectivity and reliance on precious metal electrodes. In this work, we present a simple solution to this long-standing challenge: Switching the potential waveform from classical direct current to rapid alternating polarity renders various functional groups compatible and enables the reaction on sustainable carbon-based electrodes (amorphous carbon). This breakthrough enabled access to valuable molecules that range from useful unnatural amino acids to promising polymer building blocks from readily available carboxylic acids, including biomass-derived acids. Preliminary mechanistic studies implicate the role of waveform in modulating the local pH around the electrodes and the crucial role of acetone as an unconventional reaction solvent for Kolbe reaction.

Alternating the current direction

Waveform-controlled electrolysis enables the carbon-carbon coupling of carboxylic acids.

Interrogating the Mechanistic Features of Ni(I)-Mediated Aryl Iodide Oxidative Addition Using Electroanalytical and Statistical Modeling Techniques

While the oxidative addition of Ni(I) to aryl iodides has been commonly proposed in catalytic methods, an in-depth mechanistic understanding of this fundamental process is still lacking. Herein, we describe a detailed mechanistic study of the oxidative addition process using electroanalytical and statistical modeling techniques. Electroanalytical techniques allowed rapid measurement of the oxidative addition rates for a diverse set of aryl iodide substrates and four classes of catalytically relevant complexes (Ni(MeBPy), Ni(MePhen), Ni(Terpy), and Ni(BPP)). With >200 experimental rate measurements, we were able to identify essential electronic and steric factors impacting the rate of oxidative addition through multivariate linear regression models. This has led to a classification of oxidative addition mechanisms, either through a three-center concerted or halogen-atom abstraction pathway based on the ligand type. A global heat map of predicted oxidative addition rates was created and shown applicable to a better understanding of the reaction outcome in a case study of a Ni-catalyzed coupling reaction.

Computational approaches streamlining drug discovery

Computer-aided drug discovery has been around for decades, although the past few years have seen a tectonic shift towards embracing computational technologies in both academia and pharma. This shift is largely defined by the flood of data on ligand properties and binding to therapeutic targets and their 3D structures, abundant computing capacities and the advent of on-demand virtual libraries of drug-like small molecules in their billions. Taking full advantage of these resources requires fast computational methods for effective ligand screening. This includes structure-based virtual screening of gigascale chemical spaces, further facilitated by fast iterative screening approaches. Highly synergistic are developments in deep learning predictions of ligand properties and target activities in lieu of receptor structure. Here we review recent advances in ligand discovery technologies, their potential for reshaping the whole process of drug discovery and development, as well as the challenges they encounter. We also discuss how the rapid identification of highly diverse, potent, target-selective and drug-like ligands to protein targets can democratize the drug discovery process, presenting new opportunities for the cost-effective development of safer and more effective small-molecule treatments.