Oxidant-free Conditions Research Articles

Electrochemical oxidative cyclization of alkenes, boronic acids, and dichalcogenides to access chalcogenated boronic esters and 1,3-diols

A sustainable, environmentally benign electrochemical oxidative three-component cyclization of allylic alcohols, boronic acids, and dichalcogenides under metal-free and oxidant-free conditions has been developed.

Electrochemical selective annulative amino-ketalization and amino-oxygenation of 1,6-enynes

A new electrochemical selective annulative amino-ketalization and amino-oxygenation of 1,6-enynes with disulfonimides and alcohols is reported, producing a series of functionalized benzofurans under catalyst- and oxidant-free conditions. The annulative aminoketalization proceeds with simple short-chain alcohols such as methanol, ethanol and n-propanol as O-nucleophilic reagents, while the reaction occurs in the annulative aminooxygenation direction in the presence of water and large steric sec-butyl alcohol (SBA).

An electrochemical method for deborylative selenylation of arylboronic acids under metal- and oxidant-free conditions

An electrochemical deborylative selenylation of arylboronic acids has been developed to produce aryl selenoethers in good yields, whose practicability has been highlighted through the synthesis of bioactive molecules and gram-scale preparation.

Borane-catalyzed cascade Friedel-Crafts alkylation/[1,5]-hydride transfer/Mannich cyclization to afford tetrahydroquinolines.

An unprecedented redox-neutral annulation reaction of tertiary anilines with electron-deficient alkynes was developed that proceeds through a cascade Friedel–Crafts alkylation/[1,5]-hydride transfer/Mannich cyclization sequence. Under B(C6F5)3 catalysis, a range of functionalized 1,2,3,4-tetrahydroquinolines were facilely constructed in moderate to good yields with exclusive 3,4-anti-stereochemistry. The commercial availability of the catalyst and the high atom and step economy of the procedure, together with metal-free and external oxidant-free conditions, make this an attractive method in organic synthesis.

Electrochemical selenium-π-acid promoted hydration of alkynyl phosphonates.

An unprecedented electrochemical selenium-π-acid promoted hydration of internal alkynes bearing a phosphonate auxiliary was described. Thus, valuable (hetero)aryl and alkyl ketones could be accessed under mild, metal- and external oxidant-free conditions. This protocol features high atom-economy, good chemo- and regio-selectivity, excellent functional group tolerance and easily transformable products. Control experiments demonstrate that phosphonate assistance is essential for this transformation.

Electrochemical-induced benzyl C–H amination towards the synthesis of isoindolinones via aroyloxy radical-mediated C–H activation

A novel electrochemical strategy for the synthesis of valuable isoindolinones has been developed with the use of simple o-alkylbenzoic acid and alkyl nitrile as starting materials under metal-catalyst and external oxidant-free conditions.

Ru(II)-Catalyzed Regioselective C-N Bond Formation on Benzothiazoles Employing Acyl Azide as an Amidating Agent.

A Ru(II)-catalyzed regioselective direct ortho-amidation of 2-aryl benzo[d]thiazoles employing acyl azides as a nitrogen source has been accomplished. This approach utilizes the efficiency of benzothiazole as a directing group and the role of acyl azide as an effective amidating agent toward C–N bond formation, thereby evading the general Curtius rearrangement. The protocol highlights significant functional group tolerance, single-step, and external oxidant-free conditions, with the release of only innocuous molecular nitrogen as the byproduct. The reaction mechanism and the intermediates associated with this selective Ru-catalyzed reaction have been investigated using ESI-MS. The protocol also aided in the construction of ortho-amidated β-carbolines, unveiling another class of fluorescent molecules.

Electrochemical Bromination of Glycals.

Herein, the convenient one-step electrochemical bromination of glycals using Bu4NBr as the brominating source under metal-catalyst-free and oxidant-free reaction conditions was described. A series of 2-bromoglycals bearing different electron-withdrawing or electron-donating protective groups were successfully synthesized in moderate to excellent yields. The coupling of tri-O-benzyl-2-bromogalactal with phenylacetylene, potassium phenyltrifluoroborate, or a 6-OH acceptor was achieved to afford 2C-branched carbohydrates and disaccharides via Sonogashira coupling, Suzuki coupling, and Ferrier rearrangement reactions with high efficiency. The radical trapping and cyclic voltammetry experiments indicated that bromine radicals may be involved in the reaction process.

Electrochemical Oxidative C[sbnd]H Phosphonylation of thiazole derivatives in ambient conditions

• Direct electrochemical C2 phosphonylation of thiazole derivatives under mild conditions. • The avoidance of external metal, additive and chemical-oxidant. • Facile access to various phosphorus compounds containing multi heteroatoms. • An atom economic system with simple operation and wide substrate scope. We herein report a direct electrochemical dehydrogenative C H phosphonylation of thiazoles derivatives with H 2 evolution. Employing electricity as the green and sole oxidant, cheap metal as electrode, the anodic oxidation together with cathodic hydrogen evolution process provides a green and efficient strategy for C H phosphonylation. A diverse range of phosphorus products were constructed under external metal and oxidant-free conditions at ambient temperature, featuring atom economy, simple operation and wide reaction scope.

A Metal-Free Visible-Light Photoredox Construction and Direct C-H Functionalization of Pyridines: Green Synthesis of Polysubstituted Picolinaldehydes.

The development of a novel environmental benign and sustainable synthetic method for highly efficient construction and direct C-H functionalization of N-heterocycles remains a pivotal central research topic for organic and medicinal chemistry. Herein, a novel visible-light-enabled biomimetic aza-6π electrocyclization for efficient assembly of diverse pyridines and further tandem Minisci-type reaction were developed. A broad spectrum of polysubstituted picolinaldehydes were readily constructed with high efficacy and good functional group tolerance under metal- and oxidant-free conditions.

Electrochemical Selenylative Carbannulation of Biaryl Ynones to Seleno-Dibenzocycloheptenones/Spiro[5.5]Trienones.

Electrooxidative-induced synthesis of structurally diverse seleno-dibenzocyclohepten-5-ones and seleno-spiro[5.5]trienones by selenylative carbannulation of biaryl ynones with diaryl diselenide has been developed. The switchable reactivity, intramolecular ortho-annulation or dearomative ipso-annulation, is directed by the substituent present on the ortho-aryl group of aryl-ynone. The prominent features of this method include metal-free, external chemical oxidant-free conditions, and readily accessible substrates.

Generation of Iminoxyl Radicals by Photoredox Catalysis Enables Oxidant-Free Hydroxygenation of β,γ-Unsaturated Oximes

AbstractA visible-light photocatalytic generation of iminoxyl radicals has been accomplished under oxidant-free conditions. This approach offers a mild, atom-economical, and redox-neutral synthesis of 5-methylisoxazolines through radical hydroxygenation of β,γ-unsaturated oximes in the absence of an additional hydrogen source.

Electrochemical Generation of a Nonstabilized Azomethine Ylide: Access to Substituted N-Heterocycles.

Azomethine ylides are fascinating 1,3-dipoles for [3 + 2] cycloaddition reactions toward the construction of N-heterocycles. Herein, an efficient and environmentally benign electrochemical approach for the generation of a nonstabilized azomethine ylide has been established under metal-free and external oxidant-free conditions. The resulting 1,3-dipole undergoes a [3 + 2] cycloaddition reaction with olefins. This electrosynthetic methodology indulges a straightforward and facile approach for the construction of substituted pyrrolidines.

Electro‐Oxidative Coupling of Azoles with 2‐ and 3‐Haloindoles/Thiophenes Providing Access to 2/3‐Halo(Azol‐1‐Yl)Indoles/Thiophenes

AbstractThis report discloses an electrochemical oxidative C−H/N−H cross coupling method for the synthesis of C‐2/C‐3 azolated halo‐indoles/thiophenes under metal catalyst‐free and external chemical oxidant free condition. Hydrogen gas was the only byproduct of this C−H/N−H cross‐coupling reaction. The synthetic utility of this electrochemical approach is highlighted by its easy scalabity and compatibility with highly functional indoles and azoles. The retention of halogen on the heterocycles could serve as a useful functional group for future late‐stage modifications.magnified image

Highly efficient photocatalytic dehydrogenative coupling of amines with supported platinum catalyst under the oxidant-free conditions

A highly efficient photocatalytic dehydrogenative coupling (PDC) of amines to prepare value-added imines has been developed under the mild conditions. A complete conversion of benzylamine with a 99% selectivity of N-benzylidenebenzylamine could be obtained using the 2%Pt@g-C3N4 as photocatalyst in the absence of hydrogen acceptor at room temperature. Moreover, the relationship between the physical properties of different photocatalysts and their activities has been discussed according to the characterization results of the XRD, BET, SEM, TEM, and XPS techniques. Next, the PDC of different amines have been further investigated, where ca. 70.2%–99.0% yields of corresponding imines were attained. Finally, based on the experimental results and heterogeneous catalytic principle, a possible reaction mechanism for the PDC of benzylamine is proposed.

Electrochemically mediated trifluoromethylation of 2H-indazole derivatives using CF3SO2Na

An environmentally friendly method of electrochemical mediated regioselective C-3 trifluoromethylation of 2H-indazole by employing CF3SO2Na as the CF3 source was described. This reaction tolerated various functional groups and provided CH trifluoromethylated products in moderate to good yields under transition metal-free and oxidant-free reaction conditions. Mechanism experiments showed that a radical process might be involved in this transformation.

Green synthesis of 4-organylselanyl-1H-pyrazoles through electrochemical cross-dehydrogenative coupling of 1H-pyrazoles and diorganyl diselenides

An atom-economical and efficient method for synthesizing 4-organylselanyl-1H-pyrazoles through electrochemical cross-dehydrogenation coupling of N-unsubstituted pyrazoles with diorganyl diselenides under chemical oxidant-free and mild conditions was developed. This reaction not only shows good functional-group tolerance but also has high scalability.

Catalyst-free, direct electrochemical trifluoromethylation/cyclization of N-arylacrylamides using TfNHNHBoc as a CF3 source

A new electrochemical strategy for trifluoromethylation/cyclization using TfNHNHBoc as a CF3 source was established. This approach was realized by the direct electrolysis of TfNHNHBoc under external oxidant-free and catalyst-free conditions, and afforded various trifluoromethylated oxindoles with good functional group compatibility and broad substrate scope. Preliminary mechanistic studies show that the reaction proceeds by a radical process.

Electro-oxidative Intermolecular Allylic C(sp3)-H Aminations.

The oxidative intermolecular nitrogenation of C(sp3)-H bonds represents one of the most straightforward strategies to construct nitrogen-containing molecules. However, a sacrificial chemical oxidant is generally required. Herein, we describe electrochemical oxidative intermolecular allylic C(sp3)-H aminations in an undivided cell by electric current. The cross-dehydrogenative amination proceeded efficiently with ample scope under metal- and chemical oxidant-free reaction conditions, giving molecular H2 as the only byproduct.

Electrochemical Aziridination of Tetrasubstituted Alkenes with Ammonia

Ammonia (NH3) is an ideal nitrogen source in terms of availability, reactivity, safety, atom economy, environmental compatibility, and ease of isolation. However, its utility for amine synthesis is...