Recent advances in electrochemical 1,2-difunctionalization of alkenes: mechanisms and perspectives

In recent years, significant achievements have been made in the field of electroorganic chemistry regarding the difunctionalization of alkenes. Researchers have developed innovative strategies utilizing the unique reactivity of electrochemical processes to synthesize complex molecules with high regioselectivity and stereoselectivity. This technology is widely applied in the total synthesis of natural products and in the pharmaceutical industry. This article reviews the research progress in the electrochemical difunctionalization of alkenes through three different radical-mediated pathways over the past five years. It includes discussions on 1,2-stereoselective and non-diastereoselective difunctionalization reactions, rearrangements, intramolecular migrations, and cyclization processes. The summary emphasizes innovative electrode designs, reaction mechanisms, and the integration with other emerging technologies, highlighting the potential of this method in modern organic chemistry. Additionally, it aims to address current challenges and propose possible solutions, providing a promising direction for electrochemically mediated difunctionalization reactions of alkenes.

Electro-catalyzed, solvent-controlled divergent decarboxylative annulation and hydroaminomethylation of cyclic aldimines with N-arylglycines

Herein, we reported a sustainable and simple method involving electrochemical-catalyzed decarboxylative annulation and hydroaminomethylation of cyclic aldimines with N-arylglycines by switching the reaction solvents. When the reaction was carried out in MeCN/H2O or H2O, the resulting products included imidazolidine-fused sulfamidates and C4-aminomethylated cyclic aldimines, obtained in moderate to good yields, respectively. Mechanistically, a radical pathway was proposed to be involved in this approach.

The Strategies Towards Electrochemical Generation of Aryl Radicals

The advancement in electrochemical techniques has unlocked a new path for achieving unprecedented oxidations and reductions of aryl radical precursors in a controlled and selective manner. This approach facilitates the construction of aromatic carbon-carbon and carbon-heteroatom bonds. In light of the green merits and the growing importance of this technique in aryl radical chemistry, this review aims to provide an overview of the recent advance in the electrochemical generation of aryl radicals organized by the aryl radical precursor type, with a focus on the substrate scope, limitation, and underlying mechanism, thereby inspiring future work on electrochemical aryl radical generation.

Selective Oxidative Cleavage of Benzyl C-N Bond under Metal-Free Electrochemical Conditions

With the growing significance of green chemistry in organic synthesis, electrochemical oxidation has seen rapid development. Compounds undergo oxidation-reduction reactions through electron transfer at the electrode surface. This article proposes the use of electrochemical methods to achieve cleavage of the benzyl C-N bond. This method selectively oxidatively cleaves the C-N bond without the need for metal catalysts or external oxidants. Additionally, primary, secondary, and tertiary amines exhibit good adaptability under these conditions, utilizing water as the sole source of oxygen.

Electrochemically Enable N-Sulfenylation/Phosphinylation of Sulfoximines via Oxidative Dehydrocoupling Reaction

An electrochemical oxidative cross-coupling strategy for the synthesis of N-sulfenylsulfoximines from sulfoximines and thiols was accomplished, giving diverse N-sulfenylsulfoximines in moderate to good yields. Moreover, this strategy can be extended to construct the N-P bond of N-phosphinylated sulfoximines. With electrons as reagents, the oxidative dehydrogenation cross-coupling reaction proceeds smoothly in the absence of traditional redox reagents.

Electrocatalytic C-H/S-H Coupling of Amino Pyrazoles and Thiophenols: Synthesis of Amino Pyrazole Thioether Derivatives

A mild method for the C-H/S-H coupling of pyrazol-5-amines and thiophenols was developed via electrochemistry, giving diverse amino pyrazole thioether derivatives in 37-98% yields. This electrochemical reaction is sustainable and an atom-efficient approach with good functional group tolerance and scalability by avoiding metal and external chemical oxidants.

Electrochemical oxidative decarboxylative of α-oxocarboxylic acids towards the synthesis of quinazolines and quinazolinones

A mild and environmentally electrochemical method for the synthesis of quinazolines and quinazolinones has been developed through anodic oxidation decarboxylative of α-oxocarboxylic acids. The present reaction was efficiently conducted by using simple and cheap NH4I as the N-source and electrolyte in an undivided cell. The desired products, quinazolines and quinazolinones, were isolated in high yield under chemical oxidant free conditions.

Electrocatalytic Desulfurizative Amination of Thioureas to Guanidines

Guanidine has been known as an important class of N-containing molecules with a wide range of applications. Described here is a selective and efficient electrochemical approach to the synthesis of guanidines from easily accessible thioureas and amines. The key to success for this reaction is the in situ generation of a hypervalent iodine reagent as a catalyst from iodoarene by anodic oxidation. This mild desulfurizative amination presents ample substrate scope and good functional group tolerance without the use of extra stoichiometric chemical oxidants. As only electrons serve as the oxidation reagents, this method offers a more straightforward and sustainable manner toward versatile guanidines, including late-stage functionalization of pharmaceutically relevant molecules.

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.

Electrochemically enabled decyanative C(sp3)-H oxygenation of N-cyanomethylamines to formamides

Selective oxygenation of C(sp³)-H bonds adjacent to nitrogen atoms is a highly attractive strategy for synthesizing various formamide derivatives while preserving the substrate skeletons. Herein, an environmentally benign electrochemically enabled decyanative C(sp³)-H oxygenation of N-cyanomethylamines using H₂O as a carbonyl oxygen atom source is described, leading to the synthesis of a large class of formamides in good to excellent yields with a broad substrate scope under metal- and oxidant-free conditions. This electrochemical technology highlights the facile incorporation of N-formyl into some important bioactive molecules.

TEMPO-Modified Polymethacrylates as Mediators in Electrosynthesis: Influence of the Molecular Weight on Redox Properties and Electrocatalytic Activity

Homogeneous catalysts ("mediators") are frequently employed in organic electrosynthesis to control selectivity. Despite their advantages, they can have a negative influence on the overall energy and mass balance if used only once or recycled inefficiently. Polymediators are soluble redox-active polymers applicable as electrocatalysts, enabling recovery by dialysis or membrane filtration. Using anodic alcohol oxidation as an example, we have demonstrated that TEMPO-modified polymethacrylates (TPMA) can act as efficient and recyclable catalysts. In the present work, the influence of the molecular size on the redox properties and the catalytic activity was carefully elaborated using a series of TPMAs with well-defined molecular weight distributions. Cyclic voltammetry studies show that the polymer chain length has a pronounced impact on the key-properties. Together with preparative-scale electrolysis experiments, an optimum size range was identified for polymediator-guided sustainable reaction control.

Annulation Reaction of Quinoxalin-2(1H)-ones Initiated by Electrochemical Decarboxylation of N-Arylglycines

A new methodology for the synthesis of tetrahydroimidazo[1,5-a]quinoxalin-4(5H)-ones has been accomplished through annulation of quinoxalin-2(1H)-ones initiated by electrochemical decarboxylation of N-arylglycines catalyzed by ferrocene. With a pair of oxidative and reductive processes occurring among the substrates and intermediates instead of on the electrodes, the electricity consumption was decreased.

Electro-/photocatalytic alkene-derived radical cation chemistry: recent advances in synthetic applications

Alkene-derived radical cations are versatile reactive intermediates and have been widely applied in the construction of complex functionalized molecules and cyclic systems for chemical synthesis. Therefore, the synthetic application of these alkene-derived radical cations represents a powerful and green tool that can be used to achieve the functionalization of alkenes partially because the necessity of stoichiometric external chemical oxidants and/or hazardous reaction conditions is eliminated. This review summarizes the recent advances in the synthetic applications of the electro-/photochemical alkene-derived radical cations, emphasizing the key single-electron oxidation steps of the alkenes, the scope and limitations of the substrates, and the related reaction mechanisms. Using electrocatalysis and/or photocatalysis, single electron transfer (SET) oxidation of the CC bonds in the alkenes occurs, generating the alkene-derived radical cations, which sequentially enables the functionalization of translocated radical cations to occur in two ways: the first involves direct reaction with a nucleophile/radical or two molecules of nucleophiles to realize hydrofunctionalization, difunctionalization and cyclization; and the second involves the transformation of the alkene-derived radical cations into carbon-centered radicals using a base followed by radical coupling or oxidative nucleophilic coupling.

Electrochemically Enabled Cascade Cyclization Reaction of Aromatic Aldehydes and Pyrazol-5-amines: Synthesis of Bis-pyrazolo[3,4-b:4',3'-e]pyridines

A facile method for the synthesis of bis-pyrazolo[3,4-b:4',3'-e]pyridines from easily available aromatic aldehydes and pyrazol-5-amines was developed via electrochemistry. The reaction proceeded smoothly under metal and external chemical oxidant-free conditions, giving a variety of bis-pyrazolo[3,4-b:4',3'-e]pyridines in moderate yields.

Electrochemical synthesis of dipyrazolo/dipyrimidine-fused pyridines via oxidative domino cyclization of C(sp3)–H bonds

An electrochemically oxidative domino cyclization reaction of methyl azaarenes/ketones with pyrazol-5-amines and 6-amino-pyrimidine-2,4-diones was developed, providing a variety of dipyrazolo[3,4-b:4',3'-e]pyridines and dipyrimidine-fused pyridines with moderate to good yields. The reaction...

Electrochemical Oxidative Syntheses of NH-Sulfoximines, NH-Sulfonimidamides and Dibenzothiazines via Anodically Generated Hypervalent Iodine Intermediates

Herein, we report a general method for the synthesis of NH-sulfoximines and NH-sulfonimidamides through direct electrochemical oxidative catalysis involving an iodoarene(I)/iodoarene(III) redox couple. In addition, dibenzothiazines can be synthesized from [1,1'-biaryl]-2-sulfides under standard conditions. Notably, only a catalytic amount of iodoarene is required for the generation in situ of an active hypervalent iodine catalyst, which avoids the need for an excess of a hypervalent iodine reagent relative to conventional approaches. Moreover, this protocol features broad substrate scope and wide functional group tolerance, delivering the target compounds with good-to-excellent yields even for a scale of more than 10 g.

Tunable Electrosynthesis of Anthranilic Acid Derivatives via a C-C Bond Cleavage of Isatins

A facile and direct electrocatalytic C-C bond cleavage/functionalization reaction of isatins was developed. With isatins as the amino-attached C1 sources, a variety of aminobenzoates, and aminobenzamides were synthesized in moderate to good yields under mild conditions.

Electrochemical Generation and Use in Organic Synthesis of C-, O-, and N-Centered Radicals

During the last decade several research groups have been developing electrochemical procedures to access highly functionalized organic molecules. Among the most exciting advances, the possibility of using free radical chemistry has attracted the attention of the most important synthetic groups. Nowadays, electrochemical strategies based on these species with a synthetic purpose are published continuously in scientific journals, increasing the alternatives for the synthetic organic chemistry laboratories. Free radicals can be obtained in organic electrochemical reactions; thus, this review reassembles the last decade's (2010-2020) efforts of the electrosynthetic community to generate and take advantage of the C-, O-, and N-centered radicals' reactivity. The electrochemical reactions that occur, as well as the proposed mechanism, are discussed, trying to give clear information about the used conditions and reactivity of these reactive intermediate species.

Electrochemically induced synthesis of quinazolinones via cathode hydration of o-aminobenzonitriles in aqueous solutions

An efficient and practical electrochemically catalyzed transition metal-free process for the synthesis of substituted quinazolinones from simple and readily available o-aminobenzonitriles and aldehydes in water has been accomplished. I₂/base and water play an unprecedented and vital role in the reaction. By electrochemically catalysed hydrolysis of o-aminobenzonitriles, the synthesis of quinazolinones with benzaldehyde was first proposed. The synthetic utility of this method was demonstrated by gram-scale operation, as well as the preparation of bioactive N-(2,5-dichlorophenyl)-6-(2,2,2-trifluoroethoxy) pteridin-4-amine, which enables straightforward, practical and environmentally benign quinazolinone formation.

Progress and perspectives of electrochemical insights for C–H and N–H sulfonylation

A comprehensive electrosulfonylation study has been carried out via cathodic and anodic approaches for the production of organosulfone and sulfonamide derivatives.

Electrochemical Iodoamination of Indoles Using Unactivated Amines

An environmentally friendly electrochemical approach for iodoamination of various indole derivatives with a series of unactivated amines, amino acid derivatives, and benzotriazoles (more than 80 examples) has been developed. This strategy was further applied in late-stage functionalization of natural products and pharmaceuticals and gram-scale synthesis and radiosynthesis of ¹³¹I-labeled compounds. Fundamental insights into the mechanism of the reaction based on control experiments, density functional theory calculation, and cyclic voltammetry are provided.