Efficient Indirect Electrochemical Synthesis of 2-Substituted Benzoxazoles using Sodium Iodide as Mediator

NaI-Mediated Electrochemical Cyclization-Desulfurization for the Synthesis of N-Substituted 2-Aminobenzimidazoles

An electrochemical method for the synthesis of N-substituted 2-aminobenzimidazoles through a NaI-mediated desulfurization-cyclization process is reported. This electrosynthesis method utilizes cost-effective NaI as both a mediator and an electrolyte in a catalytic amount (0.2 equiv), replacing traditional oxidizing reagents. N-Substituted o-phenylenediamines and isothiocyanates undergo a thiourea formation/cyclization/desulfurization process to provide N-substituted 2-aminobenzimidazoles (55 examples, up to 98% yield) in a single reaction vessel. Importantly, this electrochemical methodology is applicable to gram-scale synthesis, maintaining reaction efficiency.

Electrochemical NaI-mediated one-pot synthesis of guanidines from isothiocyanates via tandem addition-guanylation

In this study, we present an electrochemical approach for the synthesis of guanidines from isothiocyanates and amines in a single reaction vessel. This one-pot operation takes place in aqueous media, utilizing an undivided cell setup with NaI serving as both the electrolyte and mediator. The process involves the in situ generation of thiourea, followed by electrolytic guanylation with amines. Under ambient temperature conditions, we successfully demonstrated the formation of 30 different guanidine compounds, achieving yields ranging from fair to excellent. Furthermore, the synthesis method could be carried out on a gram scale with a good yield. This protocol stands out for its cost-effectiveness, step-economical design, high tolerance towards various functional groups, and environmentally friendly reaction conditions.

Electrochemically Enabled Total Syntheses of Natural Products

Electrochemical techniques have helped to enable the total synthesis of natural products since the pioneering work of Kolbe in the mid 1800's. The electrochemical toolset grows every day and these new possibilities change the way chemists look at and think about natural products. This review provides a perspective on total syntheses wherein electrochemical techniques enabled the carbon─carbon bond formations in the skeletal assembly of important natural products, discussion of mechanistic details, and representative examples of the bond formations enabled over the last several decades. These bond formations are often distinctly different from those possible with conventional chemistries and allow assemblies complementary to other techniques.

Electrochemical Regioselective C(sp2)-H Selenylation and Sulfenylation of Substituted 2-Amino-1,4-naphthoquinones

A straightforward and efficient electrochemical method for regioselective C(sp²)-H selenylation and sulfenylation of substituted 2-amino-1,4-naphthoquinones has been unearthed. This oxidative cross-coupling reaction avoids using transition metal catalysts, oxidants, and high temperatures. The other notable advantages of this protocol are the tolerance of diverse functional groups, mild reaction conditions at ambient temperature, energy efficiency, good to excellent yields, short reaction times (in minutes), gram-scale applicability, and eco-friendliness.

Electrosynthesis of 2-Substituted Benzoxazoles via Intramolecular Shono-Type Oxidative Coupling of Glycine Derivatives

Herein, an atom-economical and eco-friendly electrochemical oxidation/cyclization of glycine derivatives through intramolecular Shono-type oxidative coupling is disclosed, leading to a variety of 2-substituted benzoxazoles in 51-85% yields. This oxidative cyclization proceeded in transition metal- and oxidant-free conditions and generated H₂ as only a byproduct. Additionally, gram-scale reactions and a broad substrate scope demonstrated the synthetic usefulness of this protocol.

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.

Synthetic Photoelectrochemistry

Photoredox catalysis (PRC) and synthetic organic electrochemistry (SOE) are often considered competing technologies in organic synthesis. Their fusion has been largely overlooked. We review state-of-the-art synthetic organic photoelectrochemistry, grouping examples into three categories: 1) electrochemically mediated photoredox catalysis (e-PRC), 2) decoupled photoelectrochemistry (dPEC), and 3) interfacial photoelectrochemistry (iPEC). Such synergies prove beneficial not only for synthetic "greenness" and chemical selectivity, but also in the accumulation of energy for accessing super-oxidizing or -reducing single electron transfer (SET) agents. Opportunities and challenges in this emerging and exciting field are discussed.

Electrochemical Cross-Dehydrogenative Coupling between Phenols and β-Dicarbonyl Compounds: Facile Construction of Benzofurans

Preparative electrochemical synthesis is an ideal method for establishing green, sustainable processes. The major benefits of an electro-organic strategy over that of conventional chemical synthesis are the avoidance of reagent waste and mild reaction conditions. Here, an intermolecular cross-dehydrogenative coupling between phenols and β-dicarbonyl compounds has been developed to build various benzofurans under undivided electrolytic conditions. Neither transition metals nor external chemical oxidants are required to facilitate the dehydrogenation and dehydration processes. The key factor in success was the use of nBu₄ NBF₄ as the electrolyte and hexafluoroisopropanol as the solvent, which play key roles in the cyclocondensation step. This electrolysis is scalable and can be used as a key step in drug synthesis. On the basis of several experimental results, the mechanism, particularly of the remarkable anodic oxidation and cyclization process, was illustrated.

Electrochemically driven P–H oxidation and functionalization: synthesis of carbamoylphosphonates from phosphoramides and alcohols

Electrochemical synthesis of carbamoylphosphonates via P–H phosphorylation and oxygenation of phosphinecarboxamides with alcohols by using n-Bu₄NI (10 mol%) as an iodine source.

Electrochemical study of fast blue BB. A green strategy for sulfination of fast blue BB

This research has led to the development of an environmentally friendly method for the synthesis of some new sulfone derivatives with high yields and without using any toxic reagents and solvents.

Electrochemical strategies for C-H functionalization and C-N bond formation

Conventional methods for carrying out carbon-hydrogen functionalization and carbon-nitrogen bond formation are typically conducted at elevated temperatures, and rely on expensive catalysts as well as the use of stoichiometric, and perhaps toxic, oxidants. In this regard, electrochemical synthesis has recently been recognized as a sustainable and scalable strategy for the construction of challenging carbon-carbon and carbon-heteroatom bonds. Here, electrosynthesis has proven to be an environmentally benign, highly effective and versatile platform for achieving a wide range of nonclassical bond disconnections via generation of radical intermediates under mild reaction conditions. This review provides an overview on the use of anodic electrochemical methods for expediting the development of carbon-hydrogen functionalization and carbon-nitrogen bond formation strategies. Emphasis is placed on methodology development and mechanistic insight and aims to provide inspiration for future synthetic applications in the field of electrosynthesis.

Electrifying Organic Synthesis

The direct synthetic organic use of electricity is currently experiencing a renaissance. More synthetically oriented laboratories working in this area are exploiting both novel and more traditional concepts, paving the way to broader applications of this niche technology. As only electrons serve as reagents, the generation of reagent waste is efficiently avoided. Moreover, stoichiometric reagents can be regenerated and allow a transformation to be conducted in an electrocatalytic fashion. However, the application of electroorganic transformations is more than minimizing the waste footprint, it rather gives rise to inherently safe processes, reduces the number of steps of many syntheses, allows for milder reaction conditions, provides alternative means to access desired structural entities, and creates intellectual property (IP) space. When the electricity originates from renewable resources, this surplus might be directly employed as a terminal oxidizing or reducing agent, providing an ultra-sustainable and therefore highly attractive technique. This Review surveys recent developments in electrochemical synthesis that will influence the future of this area.

Functionalization of N-arylglycine esters: electrocatalytic access to C-C bonds mediated by n-Bu4NI

An efficient electrocatalytic functionalization of N-arylglycine esters is reported. The protocol proceeds in an undivided cell under constant current conditions employing the simple, cheap and readily available n-Bu₄NI as the mediator. In addition, it is demonstrated that the mediated process is superior to the direct electrochemical functionalization.

Oxidant-Free C(sp2)-H Functionalization/C-O Bond Formation: A Kolbe Oxidative Cyclization Process

An anodic oxidation/cyclization of 2-arylbenzoic acids for the synthesis of dibenzopyranones has been developed. The reaction proceeds at room temperature with no oxidant or electrolyte required and exhibits a high atom economy with H₂ being the only byproduct. A series of dibenzopyranones was obtained in good to excellent yields. Urolithins A, B, and C are formally synthesized by adopting this method as a key step to demonstrate its synthetic utility.

Synthesis of 2-methylbenzoxazoles directly from N-phenylacetamides catalyzed by palladium acetate

A method to synthesize 2-methylbenzoxazoles directly from N-phenylacetamides catalyzed by Pd(OAc)₂ in moderate to excellent yields has been achieved.

Recent advances in iodine mediated electrochemical oxidative cross-coupling

This review article gives an overview of the recent development of iodine mediated electrochemical oxidative coupling reactions.

Improvement in aluminum complexes bearing a Schiff base in ring-opening polymerization of ε-caprolactone: the synergy of the N,S-Schiff base in a five-membered ring aluminum system

A series of five-membered ring aluminum complexes bearing thiol-Schiff base ligands were synthesized, and their application in the ring-opening polymerization of ε-caprolactone (CL) was investigated.

Synthetic Organic Electrochemical Methods Since 2000: On the Verge of a Renaissance

Electrochemistry represents one of the most intimate ways of interacting with molecules. This review discusses advances in synthetic organic electrochemistry since 2000. Enabling methods and synthetic applications are analyzed alongside innate advantages as well as future challenges of electroorganic chemistry.

Use of Electrochemistry in the Synthesis of Heterocyclic Structures

The preparation and transformation of heterocyclic structures have always been of great interest in organic chemistry. Electrochemical technique provides a versatile and powerful approach to the assembly of various heterocyclic structures. In this review, we examine the advance in relation to the electrochemical construction of heterocyclic compounds published since 2000 via intra- and intermolecular cyclization reactions.

Electrochemical synthesis of benzoxazoles from anilides – a new approach to employ amidyl radical intermediates

The electroorganic synthesis of a variety of benzoxazoles starting from easy accessible anilides is reported.

Electrocatalytic intramolecular oxidative annulation of N-aryl enamines into substituted indoles mediated by iodides

An electrocatalytic reaction protocol is developed for achieving intramolecular dehydrogenative annulation ofN-aryl enamines.