Two Types of Cross-Coupling Reactions between Electron-Rich and Electron-Deficient Alkenes Assisted by Nucleophilic Addition Using an Organic Photoredox Catalyst

Engineered Polymeric Carbon Nitride for Photocatalytic Diverse Functionalization of Electronic-Rich Alkenes

Engineered polymeric carbon nitride represents a promising class of metal-free semiconductor photocatalysts for organic synthesis. Herein, we utilized engineered polymeric carbon nitride nanosheets, which exhibit an increased specific surface area and band gap due to enhanced quantum confinement from vacancy enrichment. These nanosheets serve as a heterogeneous organic semiconductor photocatalyst to facilitate diverse functionalizations of electron-rich alkenes, including arylsulfonylation, aminodifluoroalkylation, and oxytrifluoromethylation. This catalytic system operates under mild conditions, offering excellent functional group compatibility and high yields. Additionally, the catalyst demonstrates outstanding recyclability and efficiency in flow reactors, highlighting its significant potential for industrial applications.

Double difunctionalization of vinyl ether tethered nucleophile with electron-deficient alkene in two-molecule photoredox system

Double difunctionalization of a vinyl ether tethered hydroxy or carbamoyl group with electron-deficient alkenes such as acrylonitrile or acrylic esters was achieved by visible-light irradiation in a two-molecule photoredox system. Use of anhydrous acetonitrile solution as a solvent promoted both dimerization of the radical cation of electron-rich alkene with electron-rich alkene and intramolecular nucleophilic addition to generate an electron-rich radical that was added to electron-deficient alkene to furnish the double difunctionalized product. A variety of electronically differentiated rich and deficient alkenes were used in the photoreaction; a simple construction of a complex carbon framework containing acetal from simple alkenes was successful under mild conditions.

Transition metal-free decarboxylative olefination of carboxylic acid salts

The cost-effective and efficient synthesis of alkenes is highly significant due to their extensive applications in both synthetic and polymer industries. A transition metal-free approach has been devised for the chemoselective olefination of carboxylic acid salts. This modular approach provides direct access to valuable electron-deficient styrenes in moderate to good yields. Detailed mechanistic studies suggest anionic decarboxylation is followed by halogen ion transfer. This halogen transfer leads to an umpolung of reactant electronics, allowing for a rate-limiting rebound elimination.

Organic Photoredox Reactions in Two-Molecule Photoredox System

Using our recent relevant results, this account shows the featured reactivities of two-molecule photoredox systems compared to one-molecule photoredox systems. The low efficiency of electron transfer processes, such as photoinduced and back-electron transfer, in the two-molecule photoredox system, furnishes unique products through different pathways. The facile replacement of photoredox catalysts with appropriate oxidation/reduction potentials in this system provides valuable insights into photoredox reactions.

Electron-Transfer Protocol for the Hydroxyalkenylation of Alkenes Using 1,2-Bis(phenylsulfonyl)ethylene

We report a protocol for alkene hydroxyalkenylation. Using a persulfate anion as a one-electron-oxidation reagent and 1,2-bis(phenylsulfonyl)ethylene as a radical acceptor in the presence of water, alkenes were converted into the corresponding 1-phenylsulfonyl-4-hydroxyalkenes in good to high yields. The hydroxyalkenylation process involves the nucleophilic hydroxylation of alkene radical cations to give β-hydroxyalkyl radicals, which, after a radical addition/β-elimination sequence, provide the products. We also report a photocatalytic protocol for alkoxyalkenylation.

Electro-/photocatalytic alkene-derived radical cation chemistry: recent advances in synthetic applications

Alkene-derived radical cations are versatile reactive intermediates and have been widely applied in the construction of complex functionalized molecules and cyclic systems for chemical synthesis. Therefore, the synthetic application of these alkene-derived radical cations represents a powerful and green tool that can be used to achieve the functionalization of alkenes partially because the necessity of stoichiometric external chemical oxidants and/or hazardous reaction conditions is eliminated. This review summarizes the recent advances in the synthetic applications of the electro-/photochemical alkene-derived radical cations, emphasizing the key single-electron oxidation steps of the alkenes, the scope and limitations of the substrates, and the related reaction mechanisms. Using electrocatalysis and/or photocatalysis, single electron transfer (SET) oxidation of the CC bonds in the alkenes occurs, generating the alkene-derived radical cations, which sequentially enables the functionalization of translocated radical cations to occur in two ways: the first involves direct reaction with a nucleophile/radical or two molecules of nucleophiles to realize hydrofunctionalization, difunctionalization and cyclization; and the second involves the transformation of the alkene-derived radical cations into carbon-centered radicals using a base followed by radical coupling or oxidative nucleophilic coupling.

Branching out: redox strategies towards the synthesis of acyclic α-tertiary ethers

Acyclic α-tertiary ethers represent a highly prevalent functionality, common to high-value bioactive molecules, such as pharmaceuticals and natural products, and feature as crucial synthetic handles in their construction. As such their synthesis has become an ever-more important goal in synthetic chemistry as the drawbacks of traditional strong base- and acid-mediated etherifications have become more limiting. In recent years, the generation of highly reactive intermediates via redox approaches has facilitated the synthesis of highly sterically-encumbered ethers and accordingly these strategies have been widely applied in α-tertiary ether synthesis. This review summarises and appraises the state-of-the-art in the application of redox strategies enabling acyclic α-tertiary ether synthesis.

9-Cyano-10-methoxycarbonylanthracene as a Visible Organic Photoredox Catalyst in the Two-Molecule Photoredox System

Visible-light-induced decarboxylative and deboronative reactions using two-molecule organic photoredox catalysts, namely, phenanthrene (Phen) and biphenyl (BP), as electron donors and 9-cyano-10-methoxycarbonylanthracene 1a as an electron acceptor were achieved. The high solubility of 1a significantly improved the reaction efficiency and product yield. In addition, the facile tuning of the oxidation potential of the electron-donor molecule via the replacement of Phen with BP enabled the application of the two-molecule photoredox system to a wide range of substrates.

Photoinduced Electron Transfer-Promoted Reactions Using Exciplex-Type Organic Photoredox Catalyst Directly Linking Donor and Acceptor Arenes

Directly linked donor and acceptor arenes, such as phenanthrene/naphthalene/biphenyl and 1,3-dicyanobenzene were found to work as photoredox catalysts in the photoreactions of indene, 2,3-dimethyl-2-butene, and 4-methoxyphenylacetic acid. The new stable organic photocatalyst forms an intramolecular exciplex (excited complex) when irradiated in a polar solvent and shows redox catalyst activity, even at low concentrations. To the best of our knowledge, this is the first example of an intramolecular exciplex working as a redox catalyst.