Using Physical Organic Chemistry To Shape the Course of Electrochemical Reactions

Electrochemical Borylation of Alkyl Halides: Fast, Scalable Access to Alkyl Boronic Esters

Herein, a fast, scalable, and transition-metal-free borylation of alkyl halides (X = I, Br, Cl) enabled by electroreduction is reported. This process provides an efficient and practical access to primary, secondary, and tertiary boronic esters at a high current. More than 70 examples, including the late-stage borylation of natural products and drug derivatives, are furnished at room temperature, thereby demonstrating the broad utility and functional-group tolerance of this protocol. Mechanistic studies disclosed that B₂cat₂ serves as both a reagent and a cathodic mediator, enabling electroreduction of difficult-to-reduce alkyl bromides or chlorides at a low potential.

Application of an Electrochemical Microflow Reactor for Cyanosilylation: Machine Learning-Assisted Exploration of Suitable Reaction Conditions for Semi-Large-Scale Synthesis

Cyanosilylation of carbonyl compounds provides protected cyanohydrins, which can be converted into many kinds of compounds such as amino alcohols, amides, esters, and carboxylic acids. In particular, the use of trimethylsilyl cyanide as the sole carbon source can avoid the need for more toxic inorganic cyanides. In this paper, we describe an electrochemically initiated cyanosilylation of carbonyl compounds and its application to a microflow reactor. Furthermore, to identify suitable reaction conditions, which reflect considerations beyond simply a high yield, we demonstrate machine learning-assisted optimization. Machine learning can be used to adjust the current and flow rate at the same time and identify the conditions needed to achieve the best productivity.

Desulfonylative Electrocarboxylation with Carbon Dioxide

Electrocarboxylation of organic halides is one of the most investigated electrochemical approaches for converting thermodynamically inert carbon dioxide (CO₂) into value-added carboxylic acids. By converting organic halides into their sulfone derivatives, we have developed a highly efficient electrochemical desulfonylative carboxylation protocol. Such a strategy takes advantage of CO₂ as the abundant C1 building block for the facile preparation of multifunctionalized carboxylic acids, including the nonsteroidal anti-inflammatory drug ibuprofen, under mild reaction conditions.

Rhodaelectro-catalyzed access to chromones via formyl C-H activation towards peptide electro-labeling

Chromones represent a privileged scaffold in medicinal chemistry and are an omnipresent structural motif in natural products. Chemically encoded non-natural peptidomimetics feature improved stability towards enzymatic degradation, cell permeability and binding affinity, translating into a considerable impact on pharmaceutical industry. Herein, a strategy for the sustainable assembly of chromones via electro-formyl C–H activation is presented. The rational design of the rhodaelectro-catalysis is guided by detailed mechanistic insights and provides versatile access to tyrosine-based fluorogenic peptidomimetics.

The chromone scaffold is present in drugs and bioactive natural products, but conventional approaches to access chromones require stoichiometric amounts of oxidants. Here, the authors report rhodaelectro-catalyzed assembly of chromones by electrochemical formyl C–H activations, providing the basis for late-stage peptide diversification.

Electrochemical Synthesis of Organic Polysulfides from Disulfides by Sulfur Insertion from S8 and an Unexpected Solvent Effect on the Product Distribution

An electrochemical synthesis of organic polysulfides through sulfur insertion from elemental sulfur to disulfides or thiols is introduced. The highly economic, low-sensitive and low-priced reaction gives a mixture of polysulfides, whose distribution can be influenced by the addition of different amounts of carbon disulfide as co-solvent. To describe the variable distribution function of the polysulfides, a novel parameter, the "absorbance average sulfur amount in polysulfides" (SAP) was introduced and defined on the basis of the "number average molar mass" used in polymer chemistry. Various organic polysulfides were synthesized with variable volume fractions of carbon disulfide, and the yield of each polysulfide was determined by quantitative 13 C NMR. Moreover, by using two symmetrical disulfides or a disulfide and a thiol as starting materials, a mixture of symmetrical and asymmetrical polysulfides could be obtained.

Aziridine synthesis by coupling amines and alkenes via an electrogenerated dication

Aziridines-three-membered nitrogen-containing cyclic molecules-are important synthetic targets. Their substantial ring strain and resultant proclivity towards ring-opening reactions makes them versatile precursors of diverse amine products^1-3, and, in some cases, the aziridine functional group itself imbues important biological (for example, anti-tumour) activity^4-6. Transformation of ubiquitous alkenes into aziridines is an attractive synthetic strategy, but is typically accomplished using electrophilic nitrogen sources rather than widely available amine nucleophiles. Here we show that unactivated alkenes can be electrochemically transformed into a metastable, dicationic intermediate that undergoes aziridination with primary amines under basic conditions. This new approach expands the scope of readily accessible N-alkyl aziridine products relative to those obtained through existing state-of-the-art methods. A key strategic advantage of this approach is that oxidative alkene activation is decoupled from the aziridination step, enabling a wide range of commercially available but oxidatively sensitive⁷ amines to act as coupling partners for this strain-inducing transformation. More broadly, our work lays the foundations for a diverse array of difunctionalization reactions using this dication pool approach.

Electrooxidative dearomatization of biaryls: synthesis of tri- and difluoromethylated spiro[5.5]trienones

Radical spirocyclization via dearomatization has emerged as an attractive strategy for the rapid synthesis of structurally diverse spiro molecules. We report the use of electrochemistry to perform an oxidative dearomatization of biaryls leading to tri- and difluoromethylated spiro[5.5]trienones in a user friendly undivided cell set-up and a constant current mode. The catalyst- and chemical oxidant-free dearomatization procedure features ample scope, and employs electricity as the green and sole oxidant.

Electrocatalysis as an enabling technology for organic synthesis

Electrochemistry has recently gained increased attention as a versatile strategy for achieving challenging transformations at the forefront of synthetic organic chemistry. Electrochemistry's unique ability to generate highly reactive radical and radical ion intermediates in a controlled fashion under mild conditions has inspired the development of a number of new electrochemical methodologies for the preparation of valuable chemical motifs. Particularly, recent developments in electrosynthesis have featured an increased use of redox-active electrocatalysts to further enhance control over the selective formation and downstream reactivity of these reactive intermediates. Furthermore, electrocatalytic mediators enable synthetic transformations to proceed in a manner that is mechanistically distinct from purely chemical methods, allowing for the subversion of kinetic and thermodynamic obstacles encountered in conventional organic synthesis. This review highlights key innovations within the past decade in the area of synthetic electrocatalysis, with emphasis on the mechanisms and catalyst design principles underpinning these advancements. A host of oxidative and reductive electrocatalytic methodologies are discussed and are grouped according to the classification of the synthetic transformation and the nature of the electrocatalyst.

Microelectrode Arrays, Dihydroxylation, and the Development of an Orthogonal Safety-Catch Linker

Construction of larger molecular libraries on an addressable microelectrode array requires a method for recovering and characterizing molecules from the surface of any electrode in the array. This method must be orthogonal to the synthetic strategies needed to build the array. We report here a method for achieving this goal that employs the site-selective dihydroxylation reaction of a simple olefin.

Tailored cobalt-salen complexes enable electrocatalytic intramolecular allylic C-H functionalizations

Oxidative allylic C–H functionalization is a powerful tool to streamline organic synthesis as it minimizes the need for functional group activation and generates alkenyl-substituted products amenable to further chemical modifications. The intramolecular variants can be used to construct functionalized ring structures but remain limited in scope and by their frequent requirement for noble metal catalysts and stoichiometric chemical oxidants. Here we report an oxidant-free, electrocatalytic approach to achieve intramolecular oxidative allylic C–H amination and alkylation by employing tailored cobalt-salen complexes as catalysts. These reactions proceed through a radical mechanism and display broad tolerance of functional groups and alkene substitution patterns, allowing efficient coupling of di-, tri- and even tetrasubstituted alkenes with N- and C-nucleophiles to furnish high-value heterocyclic and carbocyclic structures.

Oxidative allylic C–H functionalizations minimise the need for functional group activation and generate alkenyl-substituted products amenable to further chemical modifications. Here the authors report an oxidant-free, electrocatalytic approach to achieve intramolecular oxidative allylic C–H amination and alkylation by employing tailored cobalt-salen complexes as catalysts.

Electrochemical Synthesis of Cyanoformamides from Trichloroacetonitrile and Secondary Amines Mediated by the B12 Derivative

The B₁₂ derivative, heptamethyl cobyrinate, -mediated electrochemical synthesis of cyanoformamides has been developed. Aerobic oxygenation of the carbon-centered radical initiated in situ generation of the reactive acyl chloride intermediate, which led to cyanoformamides in the presence of an amine. This one-pot and scalable synthetic method has been demonstrated with 41 examples up to 94% yields with 21 new compounds. The mechanism of electrolysis mediated by the B₁₂ derivative has been proposed based on the DFT calculations.

Anodic Olefin Coupling Reactions: Elucidating Radical Cation Mechanisms and the Interplay between Cyclization and Second Oxidation Steps

Anodic olefin coupling reactions generate new bonds and ring skeletons through a net two electron process that reverses the polarity of a known, electron-rich functional group. While much of the early work on the mechanism of these reactions focused on the initial oxidation and cyclization steps of the process, the second oxidation step also plays a central role in determining the success of the reaction. Evidence supporting this observation is presented, along with evidence that optimization of this second oxidation step is not enough to pull a poor cyclization to the desired product. Successful cyclization reactions require optimization of both processes.

Bioinspired Electrolysis for Green Molecular Transformations of Organic Halides Catalyzed by B12 Complex

Naturally-occurring B₁₂ -dependent enzymes catalyze various molecular transformations that are of particular interest from the viewpoint of biological chemistry as well as synthetic organic chemistry. Inspired by the unique property of the B₁₂ -dependent enzymes, various catalytic reactions have been developed using its model complex. Among the B₁₂ model complexes, heptamethyl cobyrinate, synthesized from natural vitamin B₁₂ , is highly soluble in various organic solvents and a redox active cobalt complex with an excellent catalysis in electroorganic synthesis. The electrochemical dechlorination of pollutant organic chlorides, such as DDT, was effectively catalyzed by the B₁₂ complex. Modification of the electrode surface by the sol-gel method to immobilize the B₁₂ complex was also developed. The B₁₂ modified electrodes were effective for the dehalogenation of organic halides with high turnover numbers based on the immobilized B₁₂ complex. Electrolysis of an organic halide catalyzed by the B₁₂ complex provided dechlorinated products under anaerobic conditions, while the electrolysis under aerobic conditions afforded oxygen incorporated products, such as an ester and amide along with dechlorination. Benzotrichloride was transformed into ethylbenzoate or N,N-diethylbenzamide in the presence of ethanol or diethylamine, respectively. This amide formation was further expanded to a unique paired electrolysis. Electrochemical reductions of an alkene and alkyne were also catalyzed by the B₁₂ complex. A cobalt-hydrogen complex should be formed as a bioinspired intermediate. Using the B₁₂ complex, light-assisted electrosynthesis was also developed to save the applied energy.

Organic Electrochemistry: Expanding the Scope of Paired Reactions

Paired electrochemical reactions allow the optimization of both atom and energy economy of oxidation and reduction reactions. While many paired electrochemical reactions take advantage of perfectly matched reactions at the anode and cathode, this matching of substrates is not necessary. In constant current electrolysis, the potential at both electrodes adjusts to the substrates in solution. In principle, any oxidation reaction can be paired with any reduction reaction. Various oxidation reactions conducted on the anodic side of the electrolysis were paired with the generation and use of hydrogen gas at the cathode, showing the generality of the anodic process in a paired electrolysis and how the auxiliary reaction required for the oxidation could be used to generate a substrate for a non-electrolysis reaction. This is combined with variations on the cathodic side of the electrolysis to complete the picture and illustrate how oxidation and reduction reactions can be combined.

Evolution of Earth-Abundant 3 d-Metallaelectro-Catalyzed C-H Activation: From Chelation-Assistance to C-H Functionalization without Directing Groups

Catalyzed C-H functionalizations have emerged as a transformative platform for molecular syntheses. Despite of indisputable advances, oxidative C-H activations have been largely restricted to precious transition metals and stoichiometric amounts of chemical oxidants. In contrast, we herein discuss the potential of earth-abundant, environmentally-benign 3d transition metals for C-H activation, which has recently gained major momentum. Thus, a strategy for full resource economy has been established in our group, with green electricity as a renewable redox agent, giving valuable hydrogen as the sole byproduct under redox mediator-free conditions. In this account, we detail our accomplishments in 3d metallaelectrocatalysis towards green syntheses until March 2021.

Electrochemical C-C bond cleavage of cyclopropanes towards the synthesis of 1,3-difunctionalized molecules

Electrochemistry has a lot of inherent advantages in organic synthesis and many redox reactions have been achieved under electrochemical condition. However, the electrochemical C-C bond cleavage and functionalization reactions are less studied. Here we develop electrochemical C-C bond cleavage and 1,3-difuntionalization of arylcyclopropanes under catalyst-free and external-oxidant-free conditions. 1,3-difluorination, 1,3-oxyfluorination and 1,3-dioxygenation of arylcyclopropanes are achieved with a high chemo- and regioselectivity by the strategic choice of nucleophiles. This protocol has good functional groups tolerance and can be scaled up. Mechanistic studies demonstrate that arylcyclopropane radical cation obtained from the anode oxidation and the subsequently generated benzyl carbonium are the key intermediates in this transformation. This development provides a scenario for constructing 1,3-difunctionalized molecules.

Electrophotocatalytic Acetoxyhydroxylation of Aryl Olefins

A method for the acetoxyhydroxylation of olefins with syn stereoselectivity under electrophotocatalytic conditions is described. The procedure uses a trisaminocyclopropenium (TAC) ion catalyst with visible light irradiation under a controlled electrochemical potential to convert aryl olefins to the corresponding glycol monoesters with high chemo- and diastereoselectivity. This reaction can be performed in batch or in flow, enabling multigram synthesis of the monoester products.

Electrochemical and Photocatalytic Oxidative Coupling of Ketones via Silyl Bis-enol Ethers

Diastereoselective oxidative coupling of ketones through a silyl bis-enol ether intermediate by anodic and photocatalytic oxidation is reported. These methods provide several 1,4-diketones in good yields without the need for stoichiometric metal oxidants. The strategic use of a silicon tether enables the coupling of both aromatic and aliphatic ketones as well as the synthesis of quaternary centers. Cyclic voltammetry is used to gain insight into the oxidation events of the reaction.

Mediator-Enabled Electrocatalysis with Ligandless Copper for Anaerobic Chan-Lam Coupling Reactions

Simple copper salts serve as catalysts to effect C-X bond-forming reactions in some of the most utilized transformations in synthesis, including the oxidative coupling of aryl boronic acids and amines. However, these Chan-Lam coupling reactions have historically relied on chemical oxidants that limit their applicability beyond small-scale synthesis. Despite the success of replacing strong chemical oxidants with electrochemistry for a variety of metal-catalyzed processes, electrooxidative reactions with ligandless copper catalysts are plagued by slow electron-transfer kinetics, irreversible copper plating, and competitive substrate oxidation. Herein, we report the implementation of substoichiometric quantities of redox mediators to address limitations to Cu-catalyzed electrosynthesis. Mechanistic studies reveal that mediators serve multiple roles by (i) rapidly oxidizing low-valent Cu intermediates, (ii) stripping Cu metal from the cathode to regenerate the catalyst and reveal the active Pt surface for proton reduction, and (iii) providing anodic overcharge protection to prevent substrate oxidation. This strategy is applied to Chan-Lam coupling of aryl-, heteroaryl-, and alkylamines with arylboronic acids in the absence of chemical oxidants. Couplings under these electrochemical conditions occur with higher yields and shorter reaction times than conventional reactions in air and provide complementary substrate reactivity.

Halogen-mediated electrochemical organic synthesis

In general, halogenide anions are anodically oxidized into active species, which can be elemental halogen, halogen cations, or halogen radicals. These species subsequently react with substrates, such as olefins, ketones, or amines, to generate halogenated products. We review the mechanisms of these reactions.

Rhodaelectro-catalyzed chemo-divergent C-H activations with alkylidenecyclopropanes for selective cyclopropylations

Herein, we report on selectivity control in C-H activations with alkylidenecyclopropanes (ACPs) for the chemo-selective assembly of cyclopropanes or dienes. Thus, unprecedented rhodaelectro-catalyzed C-H activations were realized with diversely decorated ACPs with a wide substrate scope and electricity as the sole oxidant.

Chlorination Reaction of Aromatic Compounds and Unsaturated Carbon-Carbon Bonds with Chlorine on Demand

Chlorination with chlorine is straightforward, highly reactive, and versatile, but it has significant limitations. In this Letter, we introduce a protocol that could combine the efficiency of electrochemical transformation and the high reactivity of chlorine. By utilizing Cl₃CCN as the chloride source, donating up to all three chloride atom, the reaction could generate and consume the chlorine in situ on demand to achieve the chlorination of aromatic compounds and electrodeficient alkenes.

Electrosynthesis of sulfonamides from DMSO and amines under mild conditions

With DMSO as the solvent and the precursor of a -SO₂Me unit at room temperature, a novel electrochemical oxidization and amination of DMSO with amines was developed for the synthesis of sulfonamides. Our investigations reveal that this transformation may involve a radical process and an electrochemical oxidization of DMSO.

Electrochemical Synthesis of Benzimidazoles via Dehydrogenative Cyclization of Amidines

The development of efficient and sustainable methodologies for the synthesis of N-heterocycles is a constant focus of organic synthesis. Herein an electrochemical method is reported for the synthesis of benzimidazoles through dehydrogenative cyclization of easily available N-aryl amidines. The reactions were conducted under simple constant current conditions in an undivided cell without need for catalysts, chemical oxidants, or additives, and produced H₂ as the only theoretical byproduct.

Reaching the Full Potential of Electroorganic Synthesis by Paired Electrolysis

Electroorganic synthesis has recently become a rapidly blossoming research area within the organic synthesis community. It should be noted that electrochemical reaction is always a balanced reaction system with two half-cell reactions-oxidation and reduction. Most electrochemical strategies, however, typically focus on one of the two sides for the desired transformations. Paired electrolysis has two desirable half reactions running simultaneously, thus maximizing the overall margin of atom and energy economy. Meanwhile, the spatial separation between oxidation and reduction is the essential feature of electrochemistry, offering unique opportunities for the development of redox-neutral reactions that would otherwise be challenging to accomplish in a conventional reaction flask setting. This review discusses the most recent illustrative examples of paired electrolysis with special emphasis on sequential and convergent processes.

Catalyst- and Reagent-Free Formal Aza-Wacker Cyclizations Enabled by Continuous-Flow Electrochemistry

The development of efficient and sustainable methods to access saturated N-heterocycles is of great importance because of the prevalence of these structures in natural products and bioactive compounds. Pd-catalyzed aza-Wacker type cyclization is a powerful method and provides access to N-heterocycles bearing an alkene moiety available for further synthetic manipulations from readily available materials. Herein we disclose a catalyst- and reagent-free formal aza-Wacker type cyclization reaction for the synthesis of functionalized saturated N-heterocycles. Key to the success is to conduct the reactions in a continuous-flow electrochemical reactor without adding supporting electrolyte or additives. The reactions are characterized by broad tolerance of di-, tri- and tetrasubstituted alkenes.

Single-Atom Catalysts: A Sustainable Pathway for the Advanced Catalytic Applications

A heterogeneous catalyst is a backbone of modern sustainable green industries; and understanding the relationship between its structure and properties is the key for its advancement. Recently, many upscaling synthesis strategies for the development of a variety of respectable control atomically precise heterogeneous catalysts are reported and explored for various important applications in catalysis for energy and environmental remediation. Precise atomic-scale control of catalysts has allowed to significantly increase activity, selectivity, and in some cases stability. This approach has proved to be relevant in various energy and environmental related technologies such as fuel cell, chemical reactors for organic synthesis, and environmental remediation. Therefore, this review aims to critically analyze the recent progress on single-atom catalysts (SACs) application in oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and chemical and/or electrochemical organic transformations. Finally, opportunities that may open up in the future are summarized, along with suggesting new applications for possible exploitation of SACs.

Synthetic Semiconductor Photoelectrochemistry

In the field of synthetic organic chemistry, photochemical and electrochemical approaches are often considered to be competing technologies that induce single electron transfer (SET). Recently, their fusion, i. e., the "photoelectrochemical" approach, has become the focus of attention. In this approach, both solar and electrical energy are used in creative combinations. Historically, the term "photoelectrochemistry" has been used in more inorganic fields, where a photovoltaic effect exhibited by semiconducting materials is employed. Semiconductors have also been studied intensively as photocatalysts; however, they recently have taken a back seat to molecular photocatalysts. In this account, we would like to revisit semiconductor photocatalysts in the field of synthetic organic chemistry to demonstrate that semiconductor "photoelectrochemical" approaches are more than mere alternatives to molecular photochemical and/or electrochemical approaches.

Electrochemically driven stereoselective approach to syn-1,2-diol derivatives from vinylarenes and DMF

We have developed an electrochemically driven strategy for the stereoselective synthesis of protected syn-1,2-diols from vinylarenes with N,N-dimethylformamide (DMF). The newly developed system obviates the need for transition metal catalysts or external oxidizing agents, thus providing an operationally simple and efficient route to an array of protected syn-1,2-diols in a single step. This reaction proceeds via an electrooxidation of olefin, followed by a nucleophilic attack of DMF. Subsequent oxidation and nucleophilic capture of the generated carbocation with a trifluoroacetate ion is proposed, which gives rise predominantly to a syn-diastereoselectivity upon the second nucleophilic attack of DMF.

Chemoselective electrochemical reduction of nitroarenes with gaseous ammonia

Valuable aromatic nitrogen compounds can be synthesized by reduction of nitroarenes. Herein, we report electrochemical reduction of nitroarenes by a protocol that uses inert graphite felt as electrodes and ammonia as a reductant. Depending on the cell voltage and the solvent, the protocol can be used to obtain aromatic azoxy, azo, and hydrazo compounds, as well as aniline derivatives with high chemoselectivities. The protocol can be readily scaled up to >10 g with no decrease in yield, demonstrating its potential synthetic utility. A stepwise cathodic reduction pathway was proposed to account for the generations of products in turn.

Indirect Electrosynthesis with Halogen Ions as Mediators

Organic electrosynthesis has gained increasing research interest as it harvests electric current as redox regents, thereby providing a sustainable alternative to conventional approaches. Compared with direct electrosynthesis, indirect electrosynthesis employs mediator(s) to lower the overpotentials for substrate activation, and enhance the reaction efficiency and functional group compatibility by shifting the heterogenous electron transfer process to be homogenous. As one of the most versatile and cost-efficient mediators, halogen mediators are always combined with an irreversible halogenation reaction. Thus, the electrochemical reaction between halogen mediators and substrates doesn't directly controlled by the two standard potentials difference. In this account, our recent developments in the area of halogen-mediated indirect electrosynthesis are summarized. The anodically generated halogen species from halogenide salts have the abilities to undergo electron-transfer (ET) or hydrogen-atom- transfer (HAT) processes. The reaction features, scopes, limitations, and mechanistic rationalisations are discussed in this account. We hope our studies will contribute to the future developments to broaden the scope of halogen-mediated electrosynthesis.

Electrochemically Driven Radical Reactions: From Direct Electrolysis to Molecular Catalysis

Organic radicals are versatile synthetic intermediates that provide reactivities and selectivities complementary to ionic species. Despite its long history, electrochemically driven radical reactions remain limited in scope. In the past few years, there have been dramatic increase in research activity in organic electrochemistry. We have been developing electrochemical and electrophotocatalytic methods for the generation and synthetic utilization of organic radicals. In our studies, various radical species such as alkene and arene radical cations and carbon- and heteroatom-centered radicals are generated from readily available precursors through direct electrolysis, molecular electrocatalysis or molecular electrophotocatalysis. These radical species undergo various inter- and intramolecular oxidative transformations to rapidly increase molecular complexity. The simultaneous occurrence of anodic oxidation and cathodic proton reduction allows the oxidative reactions to proceed through H₂ evolution without external chemical oxidants.

Electroreductive Nickel-Catalyzed Thiolation: Efficient Cross-Electrophile Coupling for C-S Formation

Sulfur-containing molecules are of utmost topical importance towards the effective development of pharmaceuticals and functional materials. Herein, we present an efficient and mild electrochemical thiolation by cross-electrophile coupling of alkyl bromides with functionalized bench-stable thiosulfonates to access alkyl sulfides with excellent efficacy and broad functional group tolerance. Cyclic voltammetry and potentiostatic analysis were performed to elucidate mechanistic insights into this electrocatalytic thiolation reaction.

Oxidase reactions in photoredox catalysis

The nature of the terminal oxidant in oxidation reactions is an important reaction variable that can profoundly impact the mechanism, efficiency, and practicality of a synthetic protocol. One might reasonably categorize catalytic oxidation reactions into either "oxygenase" type reactions, in which the oxidant serves as an atom- or group-transfer reagent, or "oxidase" type reactions, where the oxidant is involved in catalyst turnover but does not become structurally incorporated into the product. As the field of photoredox catalysis has matured over the past decade, many successful oxygenase-type photoreactions have been reported. The development of photocatalytic oxidase reactions, on the other hand, has been somewhat slower. This tutorial review presents selected examples of some of the key classes of terminal oxidants that have been used in the design of photoredox oxidase transformations, along with the mechanistic features and benefits of each.

Shono-Type Oxidation for Functionalization of N-Heterocycles

The development of facile synthetic methods for stereodefined aliphatic cyclic amines is an important research field in synthetic organic chemistry since such scaffolds constitute a variety of natural products and biologically active compounds. N-Acyl cyclic N,O-acetals which prepared by electrochemical oxidation of the corresponding cyclic amines have proven to be useful and versatile precursors for the synthesis of such skeletons. In this Personal Account, we introduce our efforts toward the development of synthetic strategies for the diastereo- and/or enantioselective synthesis of cyclic amines by using electrochemically prepared cyclic N,O-acetals. In addition, the investigation of the "memory of chirality" in the electrooxidative methoxylation of N-acyl amino acid derivatives, the strategy for the synthesis of chiral azabicyclic compounds by utilizing electrochemical oxidation, and halogen cation-mediated synthesis of nitrogen-containing heterocycles are also described.

Electrochemical Insight into Mechanisms and Metallocyclic Intermediates of C-H Functionalization

Transition metal-catalyzed C-H activation has emerged as a powerful tool in organic synthesis and electrosynthesis as well as in the development of new methodologies for producing fine chemicals. In order to achieve efficient and selective C-H functionalization, different strategies have been used to accelerate the C-H activation step, including the incorporation of directing groups in the substrate that facilitate coordination to the catalyst. In this review, we try to underscore that the understanding the mechanisms of the catalytic cycle and the reactivity or redox activity of the key metal cyclic intermediates in these reactions is the basis for controlling the selectivity of synthesis and electrosynthesis. Combination of the electrosynthesis and voltammetry with traditional synthetic and physico-chemical methods allows one to achieve selective transformation of C-H bonds to functionalized C-C or C-X (X=heteroatom or halogen) bonds which may encourage organic chemists to use it in the future more often. The possibilities and the benefits of electrochemical techniques are analyzed and summarized.