Electrooxidative 1,2-Bromoesterification of Alkenes with Acids and N-Bromosuccinimide

Stabilized Carbon-Centered Radical-Mediated Carbosulfenylation of Styrenes: Modular Synthesis of Sulfur-Containing Glycine and Peptide Derivatives

Sulfur-containing amino acids and peptides play critical roles in organisms. Thiol-ene reactions between the thiol residues of L-cysteine and the alkenyl fragments in the designed coupling partners serve as primary tools for constructing C─S bonds in the synthesis of unnatural sulfur-containing amino acid derivatives. These reactions are favored due to the preference for hydrogen transfer from thiol to β-sulfanyl carbon radical intermediates. In this paper, the study proposes utilizing carbon-centered radicals stabilized by the capto-dative effect, generated under photocatalytic conditions from N-aryl glycine derivatives. The aim is to compete with the thiol hydrogen, enabling radical C─C bond formation with β-sulfanyl carbon radicals. This protocol is robust in the presence of air and water, offers significant potential as a modular and efficient platform for synthesizing sulfur-containing amino acids and modifying peptides, particularly with abundant disulfides and styrenes.

Electrochemical C-H Sulfonylation of Hydrazones

We have developed an electrochemical method for the direct C-H sulfonylation of aldehyde hydrazones using sodium sufinates as the sulfonylating agent under supporting electrolyte-free conditions. This straightforward sulfonylation strategy afforded a library of (E)-sufonylated hydrazones with high tolerance of various functional groups. The radical pathway of this reaction has been revealed by the mechanistic studies.

Ni-Catalyzed Reductive Fluoroalkylacylation of Alkynes for the Steroselective Synthesis of Fluoroalkylated Enones

A Ni-catalyzed three-component reductive fluoroalkylacylation of alkynes with fluoroalkyl halides and acyl chlorides is presented. This dicarbofunctionalization provides an efficient method for the synthesis of fluoroalkyl-incorporated enones under mild conditions with high yields and excellent regioselectivity and stereoselectivity.

Directed Copper-Catalyzed Tandem Radical Cyclization Reaction of Alkyl Bromides and Unactivated Olefins

The free radical cyclization reaction is a promising strategy for ring framework formation. Herein, we report a copper-catalyzed tandem radical cyclization strategy for preparing substituted lactam derivatives. This reaction proceeds through a radical coupling approach, which not only allows a wide range of alkenes but also is quite compatible with the primary, secondary, and tertiary radicals. In addition, density functional theory calculations were performed to gain insights into the reaction mechanism.

Multicomponent reactions and photo/electrochemistry join forces: atom economy meets energy efficiency

Visible-light photoredox catalysis has been regarded as an extremely powerful tool in organic chemistry, bringing the spotlight back to radical processes. The versatility of photocatalyzed reactions has already been demonstrated to be effective in providing alternative routes for cross-coupling as well as multicomponent reactions. The photocatalyst allows the generation of high-energy intermediates through light irradiation rather than using highly reactive reagents or harsh reaction conditions. In a similar vein, organic electrochemistry has experienced a fruitful renaissance as a tool for generating reactive intermediates without the need for any catalyst. Such milder approaches pose the basis toward higher selectivity and broader applicability. In photocatalyzed and electrochemical multicomponent reactions, the generation of the radical species acts as a starter of the cascade of events. This allows for diverse reactivity and the use of reagents is usually not covered by classical methods. Owing to the availability of cheaper and more standardized photo- and electrochemical reactors, as well as easily scalable flow-setups, it is not surprising that these two fields have become areas of increased research interest. Keeping these in view, this review is aimed at providing an overview of the synthetic approaches in the design of MCRs involving photoredox catalysis and/or electrochemical activation as a crucial step with particular focus on the choice of the difunctionalized reagent.

Electrochemical radical C(sp3)–H arylation of xanthenes with electron-rich arenes

An efficient electrochemical C(sp3)–H arylation of xanthenes using a carbon anode and platinum cathode as the electrodes is disclosed.

Electrochemical Oxidative Difunctionalization of Alkenes to Access α-Oxygenated Ketones

Dioxygenation of alkenes was developed by the combination of electrochemical synthesis and aerobic oxidation, leading to easy accessibility of α-oxygenated ketones in an eco-friendly fashion. Using air as the oxygen source and the absence of transition metals were the critical features of this protocol. A wide range of alkenes and N-hydroxyimides were found to be compatible and provided α-oxygenated ketones in moderate to high yields.

Mechanistic insights into 2,4-D photoelectrocatalytic removal from water with TiO2 nanotubes under dark and solar light irradiation

Removal of recalcitrant pollutants from water is a major challenge, to which the photoelectrocatalytic processes may be a solution. Applied potential plays a key role in the photocatalytic activity of the semiconductor. This paper investigated the effect of applied potential on the photoelectrocatalytic oxidation of 2,4-Dichlorophenoxyacetic acid (2,4-D) with TiO₂ nanotubular anodes under solar light irradiation. The process was investigated at constant potentials in different regions of the polarization curve: the ohmic region, the saturation region and in the region of the Schottky barrier breakdown. PEC tests were performed in aqueous solutions of 2,4-D, and in the presence of methanol or formic acid, as scavengers of OH^• radicals and holes. Results showed the main mechanism is oxidation by OH^• radicals from water oxidation, while runs with hole scavenger revealed a second mechanism of direct oxidation by holes photogenerated at the electrode surface, with high removal rates due to current doubling effect.

Linear Paired Electrolysis-Realising 200 % Current Efficiency for Stoichiometric Transformations-The Electrochemical Bromination of Alkenes

The generation of bromine by oxidation of bromide anions at the anode and reduction of molecular oxygen at the cathode to hydrogen peroxide resulted in the overall formation of two molecules of Br₂ (=four electron oxidation) by passing just two electrons through the solution. The bromine was used for the bromination of alkenes and thereby a linear paired electrolysis was attained which resulted in current efficencies of up to 200 %. Also, the diiodination of cyclohexene as well as the electrophilic aromatic bromination of an electron‐rich arene were realised both in 168 % current efficiencies.

Efficient copper(i)-catalyzed oxidative intermolecular 1,2-estersulfenylation of styrenes with peroxyesters and disulfides

A simple and practical method for the synthesis of thio-substituted esters through copper(i)-catalyzed intermolecular 1,2-estersulfenylation of styrenes with peroxyesters and disulfides was developed. In this transformation, two new C-S bond and C-O bond were constructed simultaneously under a copper catalyst system, and the transformation exhibits a broad substrate scope and good functional group compatibility. In addition, this method can also be applied to arylthiols. It should be noted that peroxyesters not only acted as nucleophilic reagents but also as oxidants.

Oxidative alkylation/alkynylation of terminal alkenes via alkylaldehyde decarbonylation and 1,2-alkynyl migration

A metal-free oxidative alkene alkylation/alkynylation of 1,4-enyn-3-ols with alkylaldehydes has been achieved, which offers a general access to the challenging quaternary carbon-containing but-3-yn-1-ones. The method features excellent functional group tolerance, broad substrate scope and exquisite selectivity, and provides a strategy for the difunctionalization of functional alkenes and utilization of alkylaldehydes as alkylating reagents through decarbonylation and 1,2-alkynyl migration.

Solvent and catalyst-free bromofunctionalization of olefins using a mechanochemical approach

Bromofunctionalizations of olefins are an important class of chemical transformations. N-Bromoimide reagents are commonly used in these reactions but catalysts and chlorinated solvents are often employed to achieve a reasonable reaction rate. In this report, we present a solvent and catalyst-free bromofunctionalization of olefins using mechanical force.

Efficient bromofunctionalization of olefins including bromolactonization, bromocycloetherification, and intermolecular bromoesterification were achieved under solvent and catalyst-free conditions using a mechanochemical approach.

Electrohalogenation of organic compounds

In this review we target sp, sp² and sp³ carbon fluorination, chlorination, bromination and iodination reactions using electrolysis as a redox medium. Mechanistic insights and substrate reactivity are also discussed.

Electrochemical tandem trifluoromethylation of allylamines/formal (3 + 2)-cycloaddition for the rapid access to CF3-containing imidazolines and oxazolidines

A straightforward and environmentally friendly synthesis of CF₃-containing imidazolines and oxazolidines has been developed through an electrochemical three-component reaction among allylamines, the Langlois reagent, and nitrile or carbonyl compounds.

Radical-mediated alkoxypolyhaloalkylation of styrenes with polyhaloalkanes and alcohols via C(sp3)–H bond cleavage

A radical-mediated alkoxypolyhaloalkylation of styrenes with polychloroalkanes and alcohols for the facile synthesis of complex polyhaloalkanes with excellent functional-group compatibility and a broad substrate scope.

Recent progress on electrochemical synthesis involving carboxylic acids

Carboxylic acids are not only essential sections of medicinal molecules, natural products and agrochemicals but also basic building blocks for organic synthesis. However, high temperature, expensive catalysts and excess oxidants are normally required for carboxylic acid group transformations. Therefore, more eco-friendly and efficient methods are urgently needed. Organic electrochemistry, as an environmentally friendly and sustainable synthetic method, can potentially avoid the above problems and is favored by more and more organic chemists. This review summarized the recent progress on the electrochemical synthesis of carboxylic acids to construct more complex compounds, emphasizing the development of electrosynthesis methodologies and mechanisms in order to attract more chemists to recognize the importance and applications of electrochemical synthesis.

Zwitterion-Catalyzed Intermolecular Bromoesterifications

Intermolecular haloesterification is an important class of transformations. The resulting products are valuable building blocks. However, it is often necessary to use super-stoichiometric amount of acid in order to compensate the low reactivity. Herein, we report a zwitterion-catalyzed intermolecular bromoesterification using acid and olefin in an equimolar ratio. Mechanistic study revealed that the charge pair in the zwitterion works synergistically in activating both NBS and carboxylic acid.

Photocatalytic dual decarboxylative alkenylation mediated by triphenylphosphine and sodium iodide

An efficient photocatalytic dual decarboxylative alkenylation of α,β-unsaturated carboxylic acids and alkyl N-hydroxyphthalimide (NHP) esters mediated by triphenylphosphine and sodium iodide has been developed. This protocol proceeds under 456-nanometer irradiation by visible blue light in the absence of transition metals or organic dye based photoredox catalysts. The reaction is successfully applied to a wide range of redox-active esters derived from aliphatic carboxylic acids (1°, 2° and 3°) and α-amino acids, enabling transformations of diverse α,β-unsaturated carboxylic acids to α,β-alkylated styrenes with high efficiency and excellent selectivity under mild conditions.

Copper(i)-catalyzed intermolecular cyanoarylation of alkenes: convenient access to α-alkylated arylacetonitriles

A novel Cu(i)-catalyzed intermolecular cyanoarylation of alkenes with diaryliodonium salts as a radical arylating reagent and tetra-butylammonium cyanide as an electrophilic cyanating reagent was established. A broad range of α-alkylated arylacetonitriles were efficiently constructed in good to excellent yields under base- and oxidant-free and mild conditions.

Electrochemically enabled functionalization of indoles or anilines for the synthesis of hexafluoroisopropoxy indole and aniline derivatives

An environmentally benign electrochemically enabled site-selective functionalization of indole or aniline derivatives with hexafluoroisopropanol in the presence of tetrabutyl ammonium hexafluorophosphate as the redox catalyst and electrolyte was demonstrated in this work. Under mild electro-oxidation conditions, a series of hexafluoroisopropoxy indole and aniline derivatives with pharmacological activity were obtained. This conversion does not need transition metals and oxidants, and has good functional group tolerance. The in vitro cytotoxicity of all compounds was evaluated by the MTT assay against four human cancer cell lines. The results revealed that hexafluoroisopropoxy indoles have good antitumor activity and compound 2i increased the intracellular levels of ROS and inhibited apoptosis in HeLa cells.

Electrocatalytic Oxidative Transformation of Organic Acids for Carbon-Heteroatom and Sulfur-Heteroatom Bond Formation

The electrolysis of organic acids has garnered increasing attention in recent years. In addition to the famous electrochemical decarboxylation known as Kolbe electrolysis, a number of other electrochemical processes have been recently established that allow for the construction of carbon-heteroatom and sulfur-heteroatom bonds from organic acids. Herein, recent advances in electrochemical C-X and S-X (X=N, O, S, Se) bond-forming reactions from five classes of organic acids and their conjugate bases, namely, carboxylic, thiocarboxylic, phosphonic, sulfinic, and sulfonic acids, are surveyed.

Metal-free decarboxylative annulation of N-arylacrylamides with vinyl acids to synthesize benzo[b]azepin-2-ones

An efficient oxidative decarbonylative (3 + 2)/(5 + 2) annulation of N-arylacrylamides with vinyl acids for the synthesis of diverse seven-membered N-heterocycles under metal-free conditions has been developed.

Electrochemical dehydrogenative cross-coupling of xanthenes with ketones

An oxidant-free electrochemical dehydrogenative cross-coupling of xanthenes and ketones for the preparation of functionalized 9-alkyl-9H-xanthenes was developed.

Transition-metal-free synthesis of CMe2CF3-containing chroman-4-ones via decarboxylative trifluoroalkylation

(NH₄)₂S₂O₈-mediated decarboxylative trifluoroalkylation of alkenes with 3,3,3-trifluoro-2,2-dimethylpropanoic acid under metal-free conditions has been described.

Recent advances in photoelectrochemical cells (PECs) for organic synthesis

The application of PECs in organic synthesis reactions and their reaction mechanisms are highlighted.

Copper-catalyzed C–H [3 + 2] annulation of N-substituted anilines with α-carbonyl alkyl bromides via C(sp3)–Br/C(sp2)–H functionalization

A copper-catalyzed C–H [3 + 2] annulation of N-substituted anilines with α-carbonyl alkyl bromides for the synthesis of 3,3′-disubstituted oxindoles is developed.

The photoredox alkylarylation of styrenes with alkyl N-hydroxyphthalimide esters and arenes involving C-H functionalization

The In(OTf)₃-promoted three-component photoredox alkylarylation of styrenes with alkyl NHP esters and arenes to access alkylated arene derivatives through C-C bond cleavage and C-H functionalization is reported. By utilizing visible-light photoredox catalysis, alkyl N-hydroxyphthalimide esters serving as alkyl carbon-centered radicals and a wide range of arenes (e.g., indoles, pyrrole, and electron-rich arenes) as nucleophiles were used to enable the introduction of various alkyl groups and aryl groups across the C[double bond, length as m-dash]C bonds with excellent selectivity and functional group tolerance.

Synthesis of Isoxazolines and Oxazines by Electrochemical Intermolecular [2 + 1 + n] Annulation: Diazo Compounds Act as Radical Acceptors

Reported herein is an unprecedented synthesis of isoxazolines and oxazines through electrochemical intermolecular annulation of alkenes with tert-butyl nitrite, in which diazo compounds serve as radical acceptors. Notably, [2 + 1 + 2] and [2 + 1 + 3] annulations occur when styrenes and allylbenzenes are used as substrates, respectively. The latter reaction undergoes group migration to form more stable radical, manifesting radical route instead of conventional 1,3-dipolar cycloaddition occurs. Moreover, scale-up experiments suggest the potential application value of these transformations in industry.