Electrochemical Cascade Reactions of 1,2,3-Benzotriazinones with Alkynes to Assemble 3,4-Dihydroisoquinolin-1(2H)-ones

An unexpected electrochemical cascade reaction of 1,2,3-benzotriazinones with alkynes to assemble 3,4-dihydroisoquinolin-1(2H)-ones has been developed, which avoids the use of pressurized H2, any metal catalysts, and stoichiometric redox agents. This route tolerates a wide range of functional groups in both reactants and can be performed under an air atmosphere. The process of continuous cathodic reduction was demonstrated by control experiments and cyclic voltammograms. Moreover, the gram-scale reaction confirmed the potential of this environmentally benign method for practical applications.

Electrochemical Reductive Bimolecular Cycloaddition of 2-Arylideneindane-1,3-diones for the Synthesis of Spirocyclopentanole Indane-1,3-diones

An electrochemical reductive bimolecular cycloaddition of 2-arylideneindane-1,3-diones has been reported for the synthesis of spirocyclopentanole indane-1,3-diones bearing five contiguous stereocenters with vicinal tetrasubstituted stereocenters, especially involving a quaternary carbon center, in moderate to good yields and excellent diastereoselectivities. The present protocol features mild reaction conditions, no external chemical redox reagents, excellent atom economy, and gram-scale synthesis. In addition, a mechanistic investigation indicates that the reactions proceed through a radical pathway.

Phosphinothio(seleno)ation of alkynes/olefins and application on the late-stage functionalization of natural products

Non-metallic catalysis has been known as a remarkable development strategy for hydrofunctionalization of unsaturated hydrocarbons. Herein, we report a unique chemically active method of BF3·OEt2 promoted multi-component, highly regioselective, and chemoselective hydrothio(seleo)phosphonylation of unsaturated hydrocarbons, which exhibits high yield and good substrate universality. The reaction mechanism was further elucidated to be Markovnikov addition by controlling experiments, 31P and 19F NMR spectra tracking experiments, X-ray diffraction analysis, and DFT calculations. Furthermore, the gram-scale attempt and the application of the reaction on the derivatization of natural products have been successfully conducted, leading to the discovery of 3as with potential anti-Parkinson's disease (PD) activities at 1 μM. This streamlined and efficient methodology has established a new platform for non-metallic Lewis acids-promoted hydrofunctionalization of unsaturated hydrocarbons and its application on new drug research.

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.

Electrochemical Nickel-Catalyzed Hydrogenation

Olefin hydrogenation is one of the most important transformations in organic synthesis. Electrochemical transition metal-catalyzed hydrogenation is an attractive approach to replace the dangerous hydrogen gas with electrons and protons. However, this reaction poses major challenges due to rapid hydrogen evolution reaction (HER) of metal-hydride species that outcompetes alkene hydrogenation step, and facile deposition of the metal catalyst at the electrode that stalls reaction. Here we report an economical and efficient strategy to achieve high selectivity for hydrogenation reactivity over the well-established HER. Using an inexpensive and bench-stable nickel salt as the catalyst, this mild reaction features outstanding substrate generality and functional group compatibility, and distinct chemoselectivity. In addition, hydrodebromination of alkyl and aryl bromides could be realized using the same reaction system with a different ligand, and high chemoselectivity between hydrogenation and hydrodebromination could be achieved through ligand selection. The practicability of our method has been demonstrated by the success of large-scale synthesis using catalytic amount of electrolyte and a minimal amount of solvent. Cyclic voltammetry and kinetic studies were performed, which support a NiII/0 catalytic cycle and the pre-coordination of the substrate to the nickel center.

Photo- and electro-chemical strategies for the activations of strong chemical bonds

The employment of light and/or electricity - alternatively to conventional thermal energy - unlocks new reactivity paradigms as tools for chemical substrate activations. This leads to the development of new synthetic reactions and a vast expansion of chemical spaces. This review summarizes recent developments in photo- and/or electrochemical activation strategies for the functionalization of strong bonds - particularly carbon-heteroatom (C-X) bonds - via: (1) direct photoexcitation by high energy UV light; (2) activation via photoredox catalysis under irradiation with relatively lower energy UVA or blue light; (3) electrochemical reduction; (4) combination of photocatalysis and electrochemistry. Based on the types of the targeted C-X bonds, various transformations ranging from hydrodefunctionalization to cross-coupling are covered with detailed discussions of their reaction mechanisms.

Electrochemical chemoselective hydrogenation of 1,4-enediones with HFIP as the hydrogen donor: scalable access to 1,4-diketones

A straightforward electrochemical protocol for efficient hydrogenation of unsaturated CC bonds has been reported in an undivided cell. A series of versatile 1,4-diketones are smoothly generated under metal-free and external-reductant-free electrolytic conditions. Moreover, the tolerance of various functional groups and decagram-scale experiments have shown the practicability and potential applications of this methodology. Moreover, a range of heterocyclic compounds were easily prepared through follow-up procedures of 1,4-diketones.

Electrochemically Mediated Oxidation of Sensitive Propargylic Benzylic Alcohols

The electrochemical oxidation of sensitive propargylic benzylic alcohols having varying substituents is reported. We describe the preparation and characterization of N-hydroxytetrafluorophthalimide (TFNHPI) and pseudo-high-throughput development of a green electrochemical oxidation protocol for sensitive propargylic benzylic alcohols that employs TFNHPI as a stable electrochemical mediator. The electrochemical oxidation of propargylic benzylic alcohols was leveraged to develop short synthetic pathways for preparing gram quantities of resveratrol natural products such as pauciflorols.

Electroreductive synthesis of polyfunctionalized pyridin-2-ones from acetoacetanilides and carbon disulfide with oxygen evolution

A chemical reductant or a sacrificial electron donor is required in any reduction reactions, generally resulting in undesired chemical waste. Herein, we report a reductant-free reductive [3 + 2 + 1] annulation of β-keto amides with CS₂ enabled by the synergy of electro/copper/base using water as an innocuous anodic sacrifice with O₂ as a sustainable by-product. This electrochemical protocol is mild and provides access to polyfunctionalized pyridin-2-ones from simple starting materials in a single step.

Hydrophosphorylation of Electron-Deficient Alkenes and Alkynes Mediated by Convergent Paired Electrolysis

A straightforward and practical strategy for hydrophosphorylation of electron-deficient alkenes and alkynes to access γ-ketophosphine oxides, enabled by a convergent paired electrolysis (CPE) in the absence of metal, base, and...