Thiobenzoic Acid-Catalyzed Cα-H Cross Coupling of Benzyl Alcohols with α-Ketoacid Derivatives

The C-H alkylation of benzyl alcohols with α-ketoacid derivatives was achieved in the presence of thiobenzoic acid with or without Ru or Ir photoredox catalysts. The thiobenzoic acid serves as a photoexcited single-electron reducing reagent and a hydrogen atom transfer catalyst, while addition of the metal photoredox catalyst assists the electron transfer and improves the reaction efficiency. Various functional groups were tolerant of the reaction conditions, and sterically hindered diols were produced in good to high yield.

Porphyrin-based porous organic polymers synthesized using the Alder-Longo method: the most traditional synthetic strategy with exceptional capacity

Porphyrin is a typical tetrapyrrole chromophore-based pigment with a special electronic structure and functionalities, which is frequently introduced into various porous organic polymers (POPs). Porphyrin-based POPs are widely used in various fields ranging from environmental and energy to biomedicine-related fields. Currently, most porphyrin-based POPs are prepared via the copolymerization of specific-group-functionalized porphyrins with other building blocks, in which the tedious and inefficient synthesis procedure for the porphyrin greatly hinders the development of such materials. This review aimed to summarize information on porphyrin-based POPs synthesized using the Alder-Longo method, thereby skipping the complex synthesis of porphyrin-bearing monomers, in which the porphyrin macrocycles are formed directly via the cyclic tetramerization of pyrrole with monomers containing multiple aldehyde groups during the polymerization process. The representative applications of porphyrin-based POPs derived using the Alder-Longo method are finally introduced, which pinpoints a clear relationship between the structure and function from the aspect of the building blocks used and porous structures. This review is therefore valuable for the rational design of efficient porphyrin-based porous organic polymer systems that may be utilized in various fields from energy-related conversion/storage technologies to biomedical science.

Pd-catalyzed Aerobic Cross-Dehydrogenative Coupling of Catechols with 2-Oxindoles and Benzofuranones: Reactivity Difference Between Monomer and Dimer

Persistent radicals, which are generated from 2-oxindole or benzofuranone dimers, are useful tools for designing the radical-based cross-coupling reaction to provide molecules containing a quaternary carbon. The persistent radical is accessible from both the dimer and monomer; however, the reactivity difference between these substrates for the oxidative cross-coupling reaction is not fully understood, most likely because of the mechanistic complexity. Here, we present details of an aerobic cross-dehydrogenative coupling (CDC) reaction using various monomers and catechols. UV-Vis analysis and mechanistic control experiments showed that the monomer is less reactive than the dimer under aerobic conditions. Our Pd(II)-BINAP-μ-hydroxo complex significantly improved the reactivity of the monomers for the aerobic CDC reaction with catechols, yielding results comparable to those of the corresponding dimer. The procedure, which enables the generation of the persistent radical in situ, is particularly useful when employing the monomer that is not readily converted to the corresponding dimer.

NHC and visible light-mediated photoredox co-catalyzed 1,4-sulfonylacylation of 1,3-enynes for tetrasubstituted allenyl ketones

The modulation of selectivity of highly reactive carbon radical cross-coupling for the construction of C-C bonds represents a challenging task in organic chemistry. N-Heterocyclic carbene (NHC) catalyzed radical transformations have opened a new avenue for acyl radical cross-coupling chemistry. With this method, highly selective cross-coupling of an acyl radical with an alkyl radical for efficient construction of C-C bonds was successfully realized. However, the cross-coupling reaction of acyl radicals with vinyl radicals has been much less investigated. We herein describe NHC and visible light-mediated photoredox co-catalyzed radical 1,4-sulfonylacylation of 1,3-enynes, providing structurally diversified valuable tetrasubstituted allenyl ketones. Mechanistic studies indicated that ketyl radicals are formed from aroyl fluorides via the oxidative quenching of the photocatalyst excited state, allenyl radicals are generated from chemo-specific sulfonyl radical addition to the 1,3-enynes, and finally, the key allenyl and ketyl radical cross-coupling provides tetrasubstituted allenyl ketones.

Electrocatalytic Activity of Polyaniline in Magnesium-Sulfur Batteries

Rechargeable magnesium-sulfur (Mg-S) batteries offer the potential for inexpensive energy storage alternatives to other metal-ion batteries for the grid scale and household applications. Despite all economic and resource advantages, Mg-S battery chemistry suffers from a complicated reaction mechanism and extremely slow reaction kinetics. To improve the kinetics, we improvise a new electrode architecture where a conductive polymer is used along with a carbon network. This report will bring an important insight of electrocatalytic activity of polyaniline, on the basis of free-radical coupling and is a completely new concept in Mg-S battery chemistry. By the combined electron spin resonance spectroscopy, X-ray photoelectron spectroscopy, and fluorescence lifetime measurements, we perceived that the polyaniline anchors the S₃^•- species from the electrolyte/catholyte through a free-radical-coupling process and thus promotes the reduction to end-discharged products, via a chemical adduct. The concept of free-radical catalysis in Mg/S batteries will open a new knowledge to enhance the active material utilization in the Mg-S batteries.

Construction of sterically congested oxindole derivatives via visible-light-induced radical-coupling

The oxindole scaffold represents an important structural feature in many natural products and pharmaceutically relevant molecules. Herein, we report a visible-light-induced modular methodology for the synthesis of complex 3,3'-disubstituted oxindole derivatives. A library of valuable fluoroalkyl-containing highly sterically congested oxindole derivatives can be synthesized by a catalytic three-component radical coupling reaction under mild conditions (metal & photocatalyst free, >80 examples). This strategy shows high functional group tolerance and broad substrate compatibility (including a wide variety of terminal or non-terminal alkenes, conjugated dienes and enynes, and a broad array of polyfluoroalkyl iodide and oxindoles), which enables modular modification of complex drug-like compounds in one chemical step. The success of solar-driven transformation, large-scale synthesis, and the late-stage functionalization of bioactive molecules, as well as promising tumor-suppressing biological activities, highlights the potential for practical applications of this strategy. Mechanistic investigations, including a series of control experiments, UV-vis spectroscopy and DFT calculations, suggest that the reaction underwent a sequential two-step radical-coupling process and the photosensitive perfluoroalkyl benzyl iodides are key intermediates in the transformation.

Metal-Free Hydropyridylation of Thioester-Activated Alkenes via Electroreductive Radical Coupling

An electrochemical hydropyridylation of thioester-activated alkenes with 4-cyanopyridines has been developed. The reactions experience a tandem electroreduction of both substrates on the cathode surface, protonation, and radical cross-coupling process, resulting in a variety of valuable pyridine variants, which contain a tertiary and even a quaternary carbon at the α-position of pyridines, in high yields. The employment of thioesters to the conjugated alkenes enables no requirement of catalyst and high temperature, representing a highly sustainable synthetic method.

Tandem Photoredox-Chiral Phosphoric Acid Catalyzed Radical-Radical Cross-Coupling for Enantioselective Synthesis of 3-Hydroxyoxindoles

A photochemical protocol that couples diarylamines and α-ketoesters to afford the chiral 3-hydroxyoxindoles through tandem photoredox and chiral phosphoric acid catalysis is developed. The reaction involves an enantioselective photochemical radical-radical cross-coupling process. The chiral phosphoric acid is discovered to play crucial roles by decreasing the reductive potentials of α-ketoesters and stereocontrolling the downstream asymmetric radical-radical cross-coupling via the formation of pentacoordinate complex.

Oxidation Potential-Guided Electrochemical Radical-Radical Cross-Coupling Approaches to 3-Sulfonylated Imidazopyridines and Indolizines

Oxidation potential-guided electrochemical radical-radical cross-coupling reactions between N-heteroarenes and sodium sulfinates have been established. Thus, simple cyclic voltammetry measurement of substrates predicts the likelihood of successful radical-radical coupling reactions, allowing the simple and direct synthetic access to 3-sulfonylated imidazopyridines and indolizines. The developed electrochemical radical-radical cross-coupling reactions to sulfonylated N-heteroarenes boast the green synthetic nature of the reactions that are oxidant- and metal-free.