A Survival Guide for the "Electro-curious"

Phosphorus-Doped Single Atom Copper Catalyst as a Redox Mediator in the Cathodic Reduction of Quinazolinones

The use of clean electric energy to activate inert compounds has garnered significant attention. Homogeneous redox mediators (RMs) in organic electrosynthesis are effective platforms for this purpose. However, understanding the RM's electronic structure under operational conditions, electron transport processes at the electrode surface, and substrate adsorption-desorption dynamics remains challenging. Here, we synthesized a Cu single-atom catalyst (SAC, named Cu─N─P@NC) with a CuN3P1 micro-coordination structure, employing it as a unique cathode redox mediator. Introducing phosphine atoms into the coordination system allowed modulation of the SAC's electronic metal-support interaction, optimizing catalyst-substrate adsorption-desorption dynamics and accelerating electrochemical reactions. Utilizing the heterogeneous SAC strategy, we achieved a novel electro-reduction coupling ring-opening reaction of inert quinazolinone frameworks. The Cu-SAC exhibited exceptionally high catalytic activity and substrate compatibility, operating smoothly at gram-scale production. Additionally, we applied the SAC to modify 11 natural product molecules. Integrating micro-coordination environment regulation and theoretical adsorption models elucidated the significant influence of electrode-RMs-substrate interactions on reaction kinetics and catalytic efficiency-a feat challenging for homogeneous RMs. This approach offers a novel pathway for advancing efficient organic electrosynthesis reactions and provides critical insights for mechanistic studies.

Electrooxidative synthesis of 1,2,3-triazolone 1-amines

A new method for the synthesis of newly reported heterocycles, namely 1,2,3-triazolone 1-amines, via electrochemically induced intramolecular N-N bond formation was developed. The process involves electrooxidative cyclization of readily available α-aminocarbonyl hydrazones, occurs under mild conditions and enables the preparation of a diverse series of target compounds, although nitrophenyl-substituted substrates undergo decomposition upon electrolysis. Cyclic voltammetry (CV) measurements were also conducted to determine the reaction mechanism and to explain the observed scope limitations. In addition, thermal behavior studies demonstrated moderate thermal stability of several synthesized 1,2,3-triazolone 1-amines in the range of 110-140 °C. Overall, this study represents a promising contribution to the electroorganic synthesis of neglected nitrogen heterocycles for various biomedical and materials science applications.

Highly-Selective Electrochemical Decarboxylative Late-Stage Functionalization of Amino Acids

A unified electrochemical decarboxylative strategy for the site-selective construction of carbon-heteroatom bonds is disclosed herein. The metal- and catalyst-free decarboxylation provides access to the functionalization of C- and N-terminus from the simple amino acid feedstock. A wide variety of primary, secondary, and tertiary acids or alcohols were well tolerated. Late-stage functionalization using α-D-galactopyranose, di-peptide, steroid derivatives, and bio-active drug molecules established the robustness and synthesis potential of our approach.

Electrochemical synthesis of allenyl silanes and allenyl boronic esters

Allenyl silanes and boronates are pivotal building blocks in organic synthesis. Nevertheless, their synthesis requires the manipulation of transition metal or highly reactive species. Hence, the development of more sustainable protocol is highly sought after. Here we show the electrochemical synthesis of allenyl silanes and allenyl boronic esters. This catalyst-free method proceeds under mild reaction conditions. The protocol for the synthesis of allenyl silanes shows an excellent efficiency and a good functional group tolerance. The allenyl silanes are isolated in good yields (28 examples, 45-95% yields) without the use of a transition metal catalyst and under mild reaction conditions. A similar protocol is developed for the synthesis of allenyl boronates, which are obtained in low to moderate yields (13 examples, 5-55% yields). Finally, a mechanism based on an oxidative generation of the silyl and boryl radicals is suggested to access these classes of allenes.

Cathode-Anode Synergy Electrosynthesis of Propanamide via a Bipolar C-N Coupling Reaction

Propanamide is a crucial synthetic intermediate in pharmaceuticals for the preparation of antibacterial and anticancer drugs. Conventional synthesis of propanamide involves the reaction of carboxylic acid derivatives with amines, which requires harsh reaction conditions, leading to an unfavorable environmental footprint. Here, we present a cathode-anode synergistic electrochemical strategy to transform nitrate and n-propanol into propanamide under ambient conditions, where both the cathode catalyst Co3O4/SiC and the anode catalyst Ti contribute distinctively to the electrochemical process. The CH3CH2CHO produced at the Ti anode can diffuse and react with the adsorbed intermediate *NH2OH on the surface of the cathode catalyst to form propanamide. The synergistic reactions at both electrodes collectively enhance the efficiency of the propanamide synthesis. This design enables efficient propanamide production in a flow cell at the gram scale with a remarkable yield of 986.13 μmol/(cm2·h) at current densities of up to 650 mA/cm2. Our reports present a new option for environmentally friendly C-N bond synthesis, and the insights can be useful for the electrosynthesis of a wider scope of amides.

Borohydride Oxidation as Counter Reaction in Reductive Electrosynthesis

An efficient reaction at the counter electrode is of key importance for the success of net oxidative and net reductive electrochemical transformations. For electrooxidative processes, cathodic proton reduction to H2 serves as the benchmark counter reaction. In contrast, net reductive electrochemical transformations have less attractive oxidative counter reactions to choose from and commonly rely on dissolution of a sacrificial anode that effectively results in stoichiometric metal consumption for the processes. In this study, we demonstrate that anodic borohydride oxidation has great potential to successfully replace the use of such sacrificial anodes for a variety of electroreductive organic transformations. This anodic transformation effectively serves as the inverse of cathodic proton reduction, producing H2 using inert carbon-based electrode materials.

TEMPO-Mediated Electrochemical α-Allylation of Tetrahydroisoquinolines

A C(sp3)-H allylation of tetrahydroisoquinolines has been developed by combining Shono oxidation with a vinylogous Mannich-type reaction. TEMPO was used as the electrocatalyst to lower the electrode potential, improving functional group compatibility. This method provided a practical and efficient tandem procedure for the α-allylation of tetrahydroisoquinolines. The reaction proceeded through the formation of an iminium cation intermediate, which was generated in situ by anodic oxidation, followed by nucleophilic addition of 2-allylazaarenes.

Synthesis of Rare 1,2,3-Triazolium-5-olates by Electrooxidative Cyclization of α-Aminocarbonyl Hydrazones

A new method for the synthesis of rare mesoionic heterocycles, namely, 1,2,3-triazolium-5-olates, via electrochemically induced intramolecular N-N bond formation was realized. The process involves electrooxidative cyclization of the readily available α-aminocarbonyl hydrazones, occurs under mild conditions, and enables the preparation of a diverse series of target mesoionics. Additionally, 1,2,3-triazolium-5-olates demonstrated high thermal stability (up to 275 °C) and feature prominent Stokes shifts (7600-8050 cm-1), which enables their application potential for analytical systems and materials science.

Electrosynthesis of Atomically Precise Au Nanoclusters

Innovation in synthesis methodologies is crucial for advancing the discovery of new materials. This work reports the electrosynthesis of a [Au13(4-tBuPhC≡C)2(Dppe)5]Cl3 nanocluster (Au13 NC) protected by alkynyl and phosphine ligands. From simple precursor, HAuCl4 and ligands, the whole synthesis is driven by a constant potential in single electrolytic cell. X-ray crystallography determines its total structure. Control experiments, cyclic voltammetry, Proton Nuclear Magnetic Resonance (1H NMR), gas chromatography, and other characterizations demonstrate that a critical tetranuclear Au(I) complex defines the electrochemical redox behavior of the reaction solution. The critical role of a base (e.g., triethylamine) is to suppress the hydrogen evolution reaction at the cathode, paving the way for the reduction of Au ions. To resolve the problem of over-reduction and deposition of Au on the cathode, pulsed electrolysis, which is specific to electrosynthesis is employed. It significantly improves the reaction rate and the isolated yield of Au13. To extend the application scope, another four NCs protected by different ligands, [Au13(4-FPhC≡C)2(Dppe)5]Cl3, [Au8(2-CF3PhC≡C)2(Dppp)4](PF6)2, [Au11(Dppp)5]Cl3, and [Au8(SC2H4Ph)2(Dppp)4]Cl2 are synthesized electrochemically, demonstrating the versatility of the strategy.

Electroorganocatalytic asymmetric Diels-Alder cycloaddition of hydroquinones with α,β-unsaturated aldehydes

The concept of combining asymmetric aminocatalysis with electrochemistry remains underexplored. Herein, we report an electrochemically driven Diels-Alder cycloaddition reaction of substituted hydroquinones with a series of enals activated by a TMS-protected prolinol catalyst, leading to optically active products with high yields and perfect enantiomeric ratios up to 99 : 1 e.r.

Highly Efficient and Stable Bifunctional Co3Ni6S8 for Electrocatalytic Oxidation of Benzyl Alcohol and Facilitation of Hydrogen Production

The electrocatalytic oxidation of benzyl alcohol (BAOR) is crucial for promoting green industrial oxidation processes and enhancing the yield and productivity of high-value chemicals. However, there are challenges in this field, such as difficult oxidation steps in alkaline electrolytes, slow reaction kinetics, and difficulty in preserving the activity of catalysts during long-term catalytic reactions. Addressing these issues and achieving synergistic reactions to improve energy utilization by combining hydrogen evolution with enhanced catalyst activity and stability warrants focused investigation. Herein, the study reports a Co3Ni6S8-based catalyst, Co0.33Ni0.67S1-10c, which can achieve the oxidation of benzyl alcohol (BA) in alkaline solution for over 350 h, with a conversion rate of BA exceeding 90% and a Faraday efficiency of benzoic acid (BAA) exceeding 99%. The hydrogen production capacity of Co0.33Ni0.67S1-10c is also evaluated in both three-electrode and dual-electrode systems. In the three-electrode system, the hydrogen evolution rate is enhanced by a factor of 9.59 compared to the absence of BA, while in the dual-electrode system, the rate is increased by a factor of 7.85. This work presents a highly efficient and durable catalyst for the oxidation of BA and its synergistic integration with hydrogen production.

Electrochemical debrominative hydrogenation/deuteration of 2-bromo-N-arylacetamides

Herein, we report a facile and efficient electro-reductive debrominative hydrogenation/deuteration of 2-bromo-N-aryl acetamides using H2O/D2O as an economical source of hydrogen/deuterium at room temperature. The reactions proceeded efficiently via C-Br bond activation, enabling facile synthesis of a range of N-substituted amides in moderate to high yields with broad functional group compatibility.

Electrochemical Benzylic C-H Carboxylation

Direct benzylic C-H carboxylation stands as a high atom economy, efficient, and convenient route for the synthesis of valuable benzylic carboxylic acids, which are of great significance in many pharmaceuticals and bioactive molecules. However, the inherent inertness of both benzylic C-H bonds and carbon dioxide presents a great challenge for further transformations. Herein, we report our efforts to overcome this obstacle via halide-promoted linear paired electrolysis to generate various benzylic carboxylic acids. Remarkably, this process is transition-metal- and base-free, making it environmentally benign and cost-effective. Besides, it is suitable for constructing a wide range of primary, secondary, and tertiary benzylic carboxylic acids under mild reaction conditions, demonstrating broad substrate scopes and good functional group tolerance. Furthermore, our protocol enables the direct synthesis of some drug molecules, including Flurbiprofen, Ibuprofen, and Naproxen, and facilitates the late-stage modification of complex compounds, showcasing the practical application in synthetic chemistry and underscores its potential to advance the synthesis of benzylic carboxylic acids and related compounds.

Proton-Modulated Nickel Hydride Electrocatalysis for the Hydrogenation of Unsaturated Bonds and Olefin Isomerization

Transition-metal hydrides stand as indispensable intermediates in both energy conversion and organic synthesis. Their electrochemical generation represents a compelling sustainable approach, enabling precise control over the reactivity and expanding the scope of electrocatalytic hydrogenation and isomerization. However, a major challenge in Ni-catalyzed electrochemical hydrogenation is the competing hydrogen evolution reaction (HER), which has led to various innovative strategies aimed at circumventing Ni-H formation. Here, we pursued an alternative approach by designing a bifunctional ligand with a pendant amine moiety to promote Ni-H formation. This design enabled selective (semi)hydrogenation of a diverse range of substrates, including terminal and internal alkynes, alkenes, and aldehydes, achieving an unprecedented substrate scope. Remarkably, we also demonstrated tunable positional selectivity for olefin isomerization by employing different types of proton sources. Our hydrogenation and isomerization method also exhibits excellent functional group tolerance, streamlining access to pharmaceuticals and their derivatives. Computational studies revealed the crucial, noninnocent role of the proton source in modulating metal hydride selectivity, either through hydrogen bonding, direct protonation of the pendant amine, or facilitation of protodemetalation.

Anion intercalation enables efficient and stable carboxylate upgrading via aqueous non-Kolbe electrolysis

Next-generation techniques for sustainable carboxylate production generate carboxylate salts as the primary outcome. To circumvent the costly conversion of carboxylate salts to acids, we demonstrate the aqueous (non-)Kolbe electrolysis process as an alternative strategy to generate downstream value-added chemicals. Upon revealing the irreversible oxidation-induced charge transfer inhibition on the graphite anode, we propose an anion intercalation strategy to mitigate the stability problem induced by the ever-increasing overpotential. In acetate decarboxylation, we observe a high Faradaic efficiency of ~95% for non-Kolbe products (methanol and methyl acetate) at wide current densities ranging from 0.05 to 1 A cm-2 and long-term stability at current densities of 0.15 and 0.6 A cm-2 for 130 and 35 h, respectively. We also extended this strategy for the upgrading of long-chain carboxylates such as propionate, butyrate, and succinate. Our work provides valuable guidance for carboxylate upgrading and extendable strategy for overcoming passivation challenges in catalysis.

Electrochemical Commodity Polymer Up- and Re-Cycling: Toward Sustainable and Circular Plastic Treatment

The demand for commodity plastics reaches unprecedented dimensions. In contrast to the well-developed plethora of methods for polymer synthesis, sustainable strategies for the end-of-life management of plastics continue to be scarce. While mechanical re-cycling often results in downgraded materials, chemical re-cycling or up-cycling offers tremendous potential for an efficient and green approach, thereby addressing the precarious treatment of post-use plastics within a circular carbon economy. Recently, electrochemistry surfaced as a uniquely powerful tool for polymer up-cycling via polymer functionalization or degradation obtaining either novel polymers with valorized properties or high-value recycled small molecules, respectively. While discussing recent progress in that domain, future perspectives of electrochemical polymer modifications until January 2025 are outlined herein.

Electrochemical Cyclization of 2,3-Allenols

An efficient electrochemical bromocyclization of allenols has been realized for the synthesis of spirocyclic 2,5-dihydrofurans. The reaction used commercially available and nontoxic KBr as the brominating source in a simple setup under open-air conditions. Notably, optically active products can be obtained from optically active 2,3-allenols without any racemization, further enhancing the synthetic utility.

Flow Electroreductive Nickel-Catalyzed Cyclopropanation of Alkenes Using gem-Dichloroalkanes

Cyclopropanes are valuable motifs in organic synthesis, widely featured in pharmaceuticals and functional materials. Herein, we report an efficient electrochemical methodology for the cyclopropanation of alkenes, leveraging a nickel-catalyzed process in continuous-flow. The developed protocol demonstrates broad substrate scope, accommodating both electron-rich and electron-poor alkenes with high functional group tolerance. Beyond dichloromethane as a feedstock methylene source, the methodology enables the synthesis of methylated, deuterated, and chloro-substituted cyclopropanes. Mechanistic investigations suggest the electro-generation of a nickel carbene as key intermediate. Notably, the reaction operates under ambient conditions, tolerates air and moisture, and achieves scalability through continuous-flow technology, offering a straightforward route to multi-gram quantities with enhanced throughput.

Electrochemical Synthesis of β-Keto Sulfones from Enol Acetates and Sulfonyl Hydrazides

A novel and environmentally friendly strategy has been developed for the efficient electrochemical synthesis of β-keto sulfones. This method enables the synthesis of β-keto sulfones by reacting easily available sulfonylhydrazide with enol acetate under mild conditions, especially without the need for transition metal catalysts or oxidants, which can achieve high yields. The scope of this reaction was systematically explored with various sulfonyl hydrazides and enol acetates. The scale-up synthesis of β-keto sulfones was successfully accomplished using an electrochemical flow cell, demonstrating the industrial applicability of this approach. Moreover, the underlying reaction mechanism was further investigated through free radical scavenging experiments and cyclic voltammetry studies.

Reaction development: a student's checklist

So you've discovered a reaction. But how do you turn this new discovery into a fully-fledged program that maximises the potential of your novel transformation? Herein, we provide a student's checklist to serve as a helpful guide for synthesis development, allowing you to thoroughly investigate the chemistry in question while ensuring that no key aspect of the project is overlooked. A wide variety of the most illuminating synthetic and spectroscopic techniques will be summarised, in conjunction with literature examples and our own insights, to provide sound justifications for their implementation towards the goal of developing new reactions.

Activity screening of Pt-CeO2 gradient films prepared by bipolar electrochemistry for electrooxidation reactions

Glassy carbon electrodes were modified with a CeO2 film and Pt nanoparticles (Pt-CeO2) for electrocatalysis. Interestingly, the oxidation of benzyl alcohol was significantly enhanced when Pt-CeO2 films were prepared by the simultaneous electrodeposition of the two materials, indicating a significant synergistic electrocatalytic activity. Subsequently, bipolar electrochemistry was employed to prepare Pt-CeO2 gradient films. Scanning electrochemical microscopy (SECM) was employed for studying local electrochemical properties at liquid/solid interfaces. SECM allowed mapping the local electrochemical performance of the Pt-CeO2 gradient films for benzyl alcohol oxidation, showing that the reaction rate is proportional to the local Pt-CeO2 surface coverage. Therefore, Pt-CeO2 deposits with different densities along the bipolar electrode offer tunable catalytic performances for benzyl alcohol oxidation. This allows identifying in a fast and straightforward way the optimal conditions for electrocatalytic processes in a more general sense because the approach, illustrated here with one specific reaction, can be easily generalized to other catalytically active surfaces.

Electrochemical Synthesis of Vinyl Sulfonates Mediated by Bromine Radicals

Vinyl sulfonates are vital intermediates in organic synthesis, serving as versatile electrophiles in various cross-coupling reactions. Despite their significance, direct methods for synthesizing vinyl sulfonates from styrenes have been limited. In this study, we introduce an innovative electrochemical approach that leverages bromine radical mediation to facilitate the direct synthesis of vinyl sulfonates, cheap nBu4NBr acts as both an electrolyte and a catalytic amount. This process involves the reaction of styrenes with sodium sulfinates and water under electrochemical conditions, offering a straightforward pathway to these compounds. The developed strategy is characterized by its high efficiency, operational simplicity, and environmentally benign nature, adhering to the principles of green chemistry while ensuring high atom economy and remarkable regioselectivity. Furthermore, this methodology proves effective for gram-scale synthesis and allows for the subsequent functionalization of vinyl sulfonate products with pharmaceutical derivatives, thus broadening the potential applications of electrochemical techniques in styrene functionalization.

Electrocatalytic Micelle-Driven Hydrodefluorination for Accessing Unprotected Monofluorinated Indoles

Toxic organic solvents and electrolytes, traditionally indispensable for electro-organic synthesis, are now being reconsidered. In developing more sustainable electro-organic synthesis, we've harnessed the aqueous micelles as solvents and electrolyte-like structures when deformed under an electric field. The technology is showcased in synthetically highly valued hydrodefluorination reactions of difluorinated indoles. This mild electrosynthetic method produces monofluorinated unprotected indole scaffolds. Our approach minimizes waste and enhances atom economy, reducing reliance on expensive and hazardous solvents and electrolytes. The surfactant's potential for recycling was verified for two cycles. Cyclic voltammetry analysis has corroborated that PS-750-M micelles in water establish a more efficient platform for hydrodefluorination. Our technology simplifies the production of monofluorinated indoles, which are crucial for many drug-like molecules.

Paired Electrosynthesis at Interdigitated Microband Array Electrodes without Intentionally Added Electrolyte: C-C Coupling of Dicyanobenzenes with Methanol

The formation of substituted benzyl alcohols from dicyanobenzenes and methanol (C-C coupling) is demonstrated as a model system for paired electrosynthesis and investigated at interdigitated microband array electrodes in a microreactor with/without intentionally added supporting electrolyte. A Pt-Pt microband array with 5 μm bands separated by 5 μm gaps is employed in a dimethyl sulfoxide (DMSO) solvent. Yields are optimized to approximately 50% at the point of 100% conversion. The mechanism is investigated by employing isotope labeling (CD3OD, CH3OD, d 6-DMSO, 13CH3OH). The methylene group (12C or 13C) is obtained with H2, D2, and DH substitution patterns, and a hypothesis for a corresponding mechanism is discussed aided with density functional theory (DFT) calculations. Implications for sustainable electrosynthesis at paired microband electrodes are discussed.

Electrochemical Cyclization-Desulfurization Approach for the Synthesis of 1,3-Benzoxazines Using Cascade C-O and C-N Bond Formation

A cost-effective, eco-friendly, and highly efficient one-pot electrochemical process has been described for the synthesis of 4H-1,3-benzoxazine and 4,5-dihydro-1,3-benzoxazepine derivatives by employing 2-aminobenzyl alcohols, 2-(2-aminophenyl)ethan-1-ol, isothiocyanate derivatives, and TBAPF6 as an electrolyte. The developed method is accomplished at 25 °C with a constant current of 20 mA. Utilizing a graphite anode and a platinum cathode in a dimethyl sulfoxide solvent, the devised metal-free electrochemical approach minimizes the production of waste and eliminates the need for external oxidizing agents. Furthermore, the synthesis of these valuable molecules by employing an electrochemical approach significantly enhances the ongoing trends in synthetic organic chemistry.

Integrating Machine Learning and Large Language Models to Advance Exploration of Electrochemical Reactions

Electrochemical C-H oxidation reactions offer a sustainable route to functionalize hydrocarbons, yet identifying suitable substrates and optimizing synthesis remain challenging. Here, we report an integrated approach combining machine learning and large language models to streamline the exploration of electrochemical C-H oxidation reactions. Utilizing a batch rapid screening electrochemical platform, we evaluated a wide range of reactions, initially classifying substrates by their reactivity, while LLMs text-mined literature data to augment the training set. The resulting ML models for reactivity prediction achieved high accuracy (>90 %) and enabled virtual screening of a large set of commercially available molecules. To optimize reaction conditions for selected substrates, LLMs were prompted to generate code that iteratively improved yields. This human-AI collaboration proved effective, efficiently identifying high-yield conditions for 8 drug-like substances or intermediates. Notably, we benchmarked the accuracy and reliability of 12 different LLMs-including LLaMA series, Claude series, OpenAI o1, and GPT-4-on code generation and function calling related to ML based on natural language prompts given by chemists to showcase potentials for accelerating research across four diverse tasks. In addition, we collected an experimental benchmark dataset comprising 1071 reaction conditions and yields for electrochemical C-H oxidation reactions.

Transition Metal-Free Direct Electrochemical Carboxylation of Organic Halides Using a Sacrificial Magnesium Anode: Straightforward Synthesis of Carboxylic Acids

The direct electrochemical carboxylation of aryl, benzyl and alkyl halides by CO2 is described using a magnesium anode and a nickel foam cathode in an undivided cell. The process employs a sacrificial anode and does not require the additional use of a transition metal catalyst or demanding conditions, as the reactions are carried out under galvanostatic mode, at -10 °C and with commercial DMF. Under these operationally simple conditions, an important range of carboxylic acids are affordable. Mechanistic investigation account for the in situ generation of a carbanionic species that is not a simple organomagnesium halide.

Enantioselective reductive cross-couplings to forge C(sp2)-C(sp3) bonds by merging electrochemistry with nickel catalysis

Motivated by the inherent benefits of synergistically combining electrochemical methodologies with nickel catalysis, we present here a Ni-catalyzed enantioselective electroreductive cross-coupling of benzyl chlorides with aryl halides, yielding chiral 1,1-diaryl compounds with good to excellent enantioselectivity. This catalytic reaction can not only be applied to aryl chlorides/bromides, which are challenging to access by other means, but also to benzyl chlorides containing silicon groups. Additionally, the absence of a sacrificial anode lays a foundation for scalability. The combination of cyclic voltammetry analysis with electrode potential studies suggests that NiI species activate aryl halides via oxidative addition and alkyl chlorides via single electron transfer.

Cathodic tandem alkylation/dearomatization of heterocycles enabled by Al-facilitated carbonyl deoxygenation

Developing efficient strategies for the deoxygenative functionalization of carbonyl compounds is crucial for enhancing the effective utilization of biomass and the upgrading of chemical feedstocks. In this study, we present an elegant cathodic reduction strategy that enables a tandem alkylation/dearomatization reaction between quinoline derivatives and aryl aldehydes/ketones in a one-pot process. Our approach can be executed via two distinct paths: the aluminum (Al)-facilitated spin-center shift (SCS) path and the Al-facilitated direct deoxygenation path. Both paths are theoretically substantiated by DFT calculations. The crux of this protocol is the in-situ activation of the alcohol intermediates by Al salts, which substantially lowers the activation energy necessary for the formation of key transition states, thereby effectively facilitating the deoxygenation process. Control experiments have not only successfully identified the intermediates but also established that the hydrogen source for the reaction is derived from water and tetrabutylammonium salt. Notably, this method is transition metal-free and compatible with water and oxygen.

Pyrolytic Carbon: An Inexpensive, Robust, and Versatile Electrode for Synthetic Organic Electrochemistry

Synthetic organic electrochemistry is recognized as one of the most sustainable forms of redox chemistry that can enable a wide variety of useful transformations. In this study, readily prepared pyrolytic carbon electrodes are explored in several powerful rAP transformations as well as C-C and C-N bond forming reactions. Pyrolytic carbon provides an alternative to classic amorphous carbon-based materials that are either expensive or ill-suited to large-scale flow reactions.

Harnessing the Reactivity of Nitroarene Radical Anions to Create Quinoline N-Oxides by Electrochemical Reductive Cyclization

Electrochemical reduction of 2-allyl-substituted nitroarenes using a simple, undivided electrochemical cell with non-precious electrodes to generate nitroarene radical anions was developed. The nitroarene radical anion intermediates participate in 1,5-hydrogen atom transfer reactions to construct quinoline N-oxides bearing aryl-, heteroaryl-, alkenyl-, benzyl-, sulfonyl-, or carboxyl groups.

eEtherification: An Electrochemical Strategy toward the Synthesis of Sterically Hindered Dialkyl Ethers from Activated Alcohols

Traditional etherification methods, although staples in synthetic chemistry, often fall short in the efficient construction of sterically hindered dialkyl ethers, especially under mild and practical conditions. Recent advances have attempted to address these limitations, typically relying on transition metal catalysts, external reductants, or harsh reaction conditions. In this work, we disclose a novel electrochemical approach that enables the synthesis of sterically hindered ethers from economically relevant and readily accessible alcohols without the need for sacrificial oxidants. Our protocol exploits mild conditions to generate reactive carbocations, which are subsequently captured by alcohol nucleophiles to yield the desired ethers. This method is cost-effective, practical, and broad in scope, providing a valuable addition to chemists' synthetic toolkit for ether synthesis.

Ruthenaelectro-catalyzed C-H phosphorylation: ortho to para position-selectivity switch

The position-selective C-H bond activation of arenes has long been a challenging topic. Herein, we report an expedient ruthenium-electrocatalyzed site-selective ortho-C-H phosphorylation of arenes driven by electrochemical hydrogen evolution reaction (HER), avoiding stoichiometric amounts of chemical redox-waste products. This strategy paved the way to achieve unprecedented ruthenaelectro-catalyzed para-C-H phosphorylation with excellent levels of site-selectivity. This electrocatalytic approach was characterized by an ample substrate scope with a broad range of arenes containing N-heterocycles, as well as several aryl/alkylphosphine oxides were well tolerated. Moreover, late-stage C-H phosphorylation of medicinal relevant drugs could also be achieved. DFT mechanistic studies provided support for an unusual ruthenium(iii/iv/ii) regime for the ortho-C-H phosphorylation.

Electrochemical C-O and C-N Arylation using Alternating Polarity in flow for Compound Libraries

Etherification and amination of aryl halide scaffolds are commonly used reactions in parallel medicinal chemistry to rapidly scan structure-activity relationships with abundant building blocks. Electrochemical methods for aryl etherification and amination demonstrate broad functional group tolerance and extended nucleophile scope compared to traditional methods. Nevertheless, there is a need for robust and scale-transferable workflows for electrochemical compound library synthesis. Herein we describe a platform for automated electrochemical synthesis of C-X arylation (X=NH, OH) in flow to access compound libraries. A comprehensive Design of Experiment (DoE) study identifies an optimal protocol which generates high yields across>30 aryl halide scaffolds, diverse amines (including electron-deficient sulfonamides, sulfoximines, amides, and anilines) and alcohols (including serine residues within peptides). Reaction sequences are automated on commercially available equipment to generate libraries of anilines and aryl ethers. The unprecedented application of potentiostatic alternating polarity in flow is essential to avoid accumulating electrode passivation. Moreover, it enables reactions to be performed in air, without supporting electrolyte and with high reproducibility over consecutive runs. Our method represents a powerful means to rapidly generate nucleophile independent C-X arylation compound libraries using flow electrochemistry.

An Electrosynthesis of 1,3,4-Oxadiazoles from N-Acyl Hydrazones

The 1,3,4-oxadiazole is a widely encountered motif in the areas of pharmaceuticals, materials, and agrochemicals. This work has established a mediated electrochemical synthesis of 2,5-disubstituted 1,3,4-oxadiazoles from N-acyl hydrazones. Using DABCO as the optimal redox mediator has enabled a mild oxidative cyclisation, without recourse to stoichiometric oxidants. In contrast to previous methods, this indirect electrochemical oxidation has enabled a broad range of substrates to be accessed, with yields of up to 83 %, and on gram scale. The simplicity of the method has been further demonstrated by the development of a one-pot procedure, directly transforming readily available aldehydes and hydrazides into valuable heterocycles.

The Future of Electro-organic Synthesis in Drug Discovery and Early Development

Electro-organic chemistry presents a promising frontier in drug discovery and early development, facilitating novel reactivity aligned with green chemistry principles. Despite this, electrochemistry is not widely used as a synthesis and manufacturing tool in drug discovery or development. This overview seeks to identify key areas that require additional research to make synthetic electrochemistry more accessible to chemists in drug discovery and early development and provide potential solutions. This includes expanding the reaction scope, simplifying rapid scale-up, developing electrode materials, and improving knowledge transfer to aid reproducibility and increase the awareness of electrochemistry. The integration of electro-organic synthesis into drug discovery and development holds the potential to enable efficient, sustainable routes toward future medicines faster than ever.

Anodic Commodity Polymer Recycling: The Merger of Iron-Electrocatalysis with Scalable Hydrogen Evolution Reaction

Plastics are omnipresent in our everyday life, and accumulation of post-consumer plastic waste in our environment represents a major societal challenge. Hence, methods for plastic waste recycling are in high demand for a future circular economy. Specifically, the degradation of post-consumer polymers towards value-added small molecules constitutes a sustainable strategy for a carbon circular economy. Despite of recent advances, chemical polymer degradation continues to be largely limited to chemical redox agents or low energy efficiency in photochemical processes. We herein report a powerful iron-catalyzed degradation of high molecular weight polystyrenes through electrochemistry to efficiently deliver monomeric benzoyl products. The robustness of the ferraelectrocatalysis was mirrored by the degradation of various real-life post-consumer plastics, also on gram scale. The cathodic half reaction was largely represented by the hydrogen evolution reaction (HER). The scalable electro-polymer degradation could be solely fueled by solar energy through a commercially available solar panel, indicating an outstanding potential for a decentralized green hydrogen economy.

Electrochemical Homo- and Crossannulation of Alkynes and Nitriles for the Regio- and Chemoselective Synthesis of 3,6-Diarylpyridines

We disclose a mediated electrochemical [2+2+2] annulation of alkynes with nitriles, forming substituted pyridines in a single step from low-cost, readily available starting materials. The combination of electrochemistry and a triarylamine redox mediator obviates the requirements of transition metals and additional oxidants. Besides the formation of diarylpyridine moieties via the homocoupling of two identical alkynes, the heterocoupling of two different alkynes depending on their electronic nature is possible, highlighting the unprecedented control of chemoselectivity in this catalytic [2+2+2] process. Mechanistic investigations like cyclic voltammetry and crossover experiments combined with DFT calculations indicate the initial oxidation of an alkyne as the key step leading to the formation of a vinyl radical cation intermediate. The utilization of continuous flow technology proved instrumental for an efficient process scale-up. The utility of the products is exemplified by the synthesis of π-extended molecules, being relevant for material or drug synthesis.

Electrochemical Deconstructive Methoxylation of Arylalcohols-A Synthetic and Mechanistic Investigation

Herein, we report a mechanistic investigation of a recently developed electrochemical method for the deconstructive methoxylation of arylalcohols. A combination of synthetic, electroanalytical, and computational experiments have been performed to gain a deeper understanding of the reaction mechanism and the structural requirements for fragmentation to occur. It was found that 2-arylalcohols undergo anodic oxidation to form the corresponding aromatic radical cations, which fragment to form oxocarbenium ions and benzylic radical intermediates via mesolytic cleavage, with further anodic oxidation and trapping of the benzylic carbocation with methanol to generate the observed methyl ether products. It was also found that the electrochemical fragmentation of 2-arylalkanols is promoted by structural features that stabilize the oxocarbenium ions and/or benzylic radical intermediates formed upon mesolytic cleavage of the aromatic radical cations. With an enhanced understanding of the reaction mechanism and the structural features that promote fragmentation, it is anticipated that alternative electrosynthetic transformations will be developed that utilize this powerful, yet underdeveloped, mode of substrate activation.

Synthesis of N-heterocyclic amides from imidazoheterocycles through convergent paired electrolysis

An efficient ring opening of imidazoheterocycles induced by a direct C-H azidation resulting in an unusual formation of N-heterocyclic amides has been successfully developed through convergent paired electrolysis. A broad scope of pyridylbenzamides could be obtained in moderate to excellent yields under exogenous-oxidant, electrolyte- and metal-free electrochemical conditions. The methodology was transferred to continuous flow conditions resulting in notable improvements particularly in terms of cost-efficiency over traditional batch versions.

Correspondence on "Organo-Mediator Enabled Electrochemical Deuteration of Styrenes"

The recently reported electrochemical, organo-mediator enabled deuteration of styrenes, a reaction referred to as "electrochemical deuterium atom transfer", differs mechanistically from reported direct electrochemical hydrogenations/deuterations only by a mediated, homogeneous SET to the substrates. By comparing direct vs. mediated processes in general and for styrene reduction, we display that Qiu's work does not change the concept of this chemistry. Experiments with mediators and the direct reduction of examples from the reported scope show that even electron-rich substrates can be reduced when our direct protocol, published six months before Qiu's work, is applied.

Electrochemically Driven α,β-Dehydrogenation of Flavanones, Azaflavanones, and Thioflavanones

α,β-Dehydrogenation of flavanones represents an ideal strategy to synthesize various flavones but remains challenging because of the requirements for rigorous conditions. Herein, a straightforward and efficient route for the synthesis of flavones via electrocatalysis is disclosed. This electro-oxidative approach shows a broad substrate scope, including azaflavanones and thioflavanones, which could be performed in an undivided cell without the removal of air or water and in the absence of metal catalysts, ligands, or external oxidants. Moreover, the combination of cyclic voltammetry, square wave voltammetry experiments, and density functional theory (DFT) calculations revealed the plausible mechanism.

Enhancing electrochemical reactions in organic synthesis: the impact of flow chemistry

Utilizing electrons directly offers significant potential for advancing organic synthesis by facilitating novel reactivity and enhancing selectivity under mild conditions. As a result, an increasing number of organic chemists are exploring electrosynthesis. However, the efficacy of electrochemical transformations depends critically on the design of the electrochemical cell. Batch cells often suffer from limitations such as large inter-electrode distances and poor mass transfer, making flow cells a promising alternative. Implementing flow cells, however, requires a foundational understanding of microreactor technology. In this review, we briefly outline the applications of flow electrosynthesis before providing a comprehensive examination of existing flow reactor technologies. Our goal is to equip organic chemists with the insights needed to tailor their electrochemical flow cells to meet specific reactivity requirements effectively. We also highlight the application of reactor designs in scaling up electrochemical processes and integrating high-throughput experimentation and automation. These advancements not only enhance the potential of flow electrosynthesis for the synthetic community but also hold promise for both academia and industry.

Electrochemical Synthesis of C(sp3)-Rich Heterocycles via Mesolytic Cleavage of Anodically Generated Aromatic Radical Cations

Herein we report an electrochemical deconstructive functionalization approach for the synthesis of C(sp3)-rich heterocycles. The reaction proceeds via the mesolytic cleavage of anodically generated aromatic radical cations and the trapping of formed carbocation intermediates with internal nucleophiles. The method has been demonstrated across various arylalcohol substrates to access a diverse range of C(sp3)-rich heterocycles including tetrahydrofuran, tetrahydropyran, and pyrrolidine scaffolds (26 examples). The electrochemical method was demonstrated on a 5 mmol scale via single pass continuous flow, which utilized lower supporting electrolyte concentration and exhibited increased productivity in relation to the batch process.

Electrochemical stereoselective borylation of Morita-Baylis-Hillman adducts to functionalized allylic boronates

Herein, we disclose a highly efficient and facile electrochemical borylation of Morita-Baylis-Hillman adducts without using any metal catalyst. This methodology demonstrates excellent regio- and stereo-selectivity, leading to a wide range of functionalized E-allylic boronates, including derivatives of ibuprofen and menthol. Under mild and straightforward conditions, this redox-neutral reaction, combined with the scalability and synthetic applications of the allylic boronate esters, underscores its potential for a wide range of applications in organic synthesis.

Total Synthesis of (±)-Anigorootin

An 11-step synthesis of the octacyclic-fused dimeric phenylphenalenone anigorootin (phytoalexin in banana plants) is reported. The synthetic strategy uses an electrochemical dimerization as the key step, which stereospecifically installs the four asymmetric centers. Mechanistic aspects of the dimerization process are discussed.

Electrochemical Postpolymerization Modification and Deconstruction of Macromolecules

Electrolysis is an emerging approach to polymer postpolymerization modification, deconstruction, and depolymerization. Electrochemical reactions are particularly appealing for macromolecular transformations because of their high selectivity, ability to be externally monitored, and intrinsic scalability. Despite these desirable features and the recent resurgent use of small-molecule electrochemical reactions, the development of macromolecular electrolysis has been limited. Herein, we highlight recent examples of polymer transformations driven by heterogeneous redox chemistry. Throughout our exploration of macromolecular electrolysis, we provide our perspective on opportunities for continued investigation in this nascent field. Specifically, we highlight how targeted reaction development through deeper mechanistic insight will expand the scope of materials that can be (de)constructed with electrochemical methods. As this insight is developed, we expect macromolecular electrolysis to emerge as a high-functioning and complementary tool for macromolecular functionalization and deconstruction.

Automated electrosynthesis reaction mining with multimodal large language models (MLLMs)

Leveraging the chemical data available in legacy formats such as publications and patents is a significant challenge for the community. Automated reaction mining offers a promising solution to unleash this knowledge into a learnable digital form and therefore help expedite materials and reaction discovery. However, existing reaction mining toolkits are limited to single input modalities (text or images) and cannot effectively integrate heterogeneous data that is scattered across text, tables, and figures. In this work, we go beyond single input modalities and explore multimodal large language models (MLLMs) for the analysis of diverse data inputs for automated electrosynthesis reaction mining. We compiled a test dataset of 65 articles (MERMES-T24 set) and employed it to benchmark five prominent MLLMs against two critical tasks: (i) reaction diagram parsing and (ii) resolving cross-modality data interdependencies. The frontrunner MLLM achieved ≥96% accuracy in both tasks, with the strategic integration of single-shot visual prompts and image pre-processing techniques. We integrate this capability into a toolkit named MERMES (multimodal reaction mining pipeline for electrosynthesis). Our toolkit functions as an end-to-end MLLM-powered pipeline that integrates article retrieval, information extraction and multimodal analysis for streamlining and automating knowledge extraction. This work lays the groundwork for the increased utilization of MLLMs to accelerate the digitization of chemistry knowledge for data-driven research.

Electrochemical deconstruction of alkyl substituted boron clusters to produce alkyl boronate esters

Closo-Hexaborate (closo-B6H62-) can engage in nucleophilic substitution reactions with a wide variety of alkyl electrophiles. The resulting functionalized boron clusters undergo oxidative electrochemical deconstruction, selectively cleaving B-B bonds while preserving B-C bonds in these species. This approach allows the conversion of multinuclear boron clusters into single boron site organoboranes. Trapped boron-based fragments were isolated from the electrochemical cluster deconstruction process, providing further mechanistic insights into the developed reaction.

Mn-Catalyzed Electrooxidative Radical Cascade Cyclization for the Synthesis of 6-Phosphorylated Quinoxalino[2,1-b]quinazolin-12-ones

Due to their important potential medicinal value, chemists are pursuing mild and efficient methods to synthesize structurally diverse quinazolinone derivatives. In this paper, a series of isocyano-tethered N-aryl quinazolinones were designed and synthesized to conduct electrocatalytic radical cascade cyclization reactions with phosphine oxides by utilizing inexpensive MnII salt as the catalyst. The desired 6-phosphorylated quinoxalino[2,1-b]quinazolin-12-ones were obtained in moderate to good yields.