Search Results (64)

In this article, we present experimental and theoretical studies of pyridine derivatives (pyDs) inspired by natural systems to investigate the electron transfer processes occurring in aqueous media and elaborate a theoretical model that adequately predicts the behavior of new derivatives. Our results might be relevant to scientific and technological applications, including energy storage, redox-active scaffolds for organic synthesis, photoredox catalysis, and new materials. The synthesis of eight pyDs is reported. To improve water solubility, six new compounds are hexafluorophosphate alkylammonium salts. The pyDs exhibit irreversible redox processes, with electron-donating substituents decreasing the cathodic peak potential while electron-withdrawing groups increase it; when both substituents are present, the latter effect prevails. A computational study was performed to investigate the electrochemical behavior of the synthesized compounds and design new electroactive pyDs. DFT calculations provided the predominant species’ redox potentials and acidity constants to elaborate Pourbaix diagrams for each compound. The synthesized molecules exhibit a two-electron-one-proton dismutation process in the water pH window. Beyond this range, stabilized radical species undergo one-electron exchange processes. We correlated experimental and calculated parameters, screening 22 additional derivatives to evaluate their electrochemical behavior, identifying potential candidates capable of performing a one-electron transfer process in the pH window of water, revealing new applications for pyDs. Full article

Visible-light photoredox catalysis using biacetyl (BA) as a low-cost photosensitizer enables the efficient formation of triarylethylenes (TAEs) via a Mizoroki–Heck-type coupling. The reaction proceeds efficiently in acetonitrile upon blue LED irradiation under anaerobic conditions. Alternatively, supramolecular viscoelastic gels have also been explored as reaction media, allowing the possibility of working under aerobic atmosphere. Mechanistic investigations by means of transient absorption spectroscopy and quenching experiments support a charge-separated intermediate pathway. Reaction quantum yield measurements further validate the efficiency of BA, demonstrating its potential as an alternative to transition-metal catalysts. Overall, this work presents a sustainable and scalable strategy for TAEs synthesis, integrating photoredox catalysis with soft material engineering. These findings pave the way for broader applications in green chemistry and functional materials. Full article

Quinazolinones, a class of nitrogen-containing heterocyclic compounds, occupy a crucial position in medicinal chemistry and materials science due to their significant application potential. In recent years, the catalytic asymmetric synthesis of axially chiral quinazolinones has emerged as a prominent research area, driven by their prospective applications in the development of bioactive molecules, design of chiral ligands, and fabrication of functional materials. This review comprehensively summarizes recent advancements in the catalytic asymmetric synthesis of axially chiral quinazolinones, with a particular focus on the construction strategies for the three major structural types: the C–N axis, N–N axis, and C–C axis. Key synthetic methodologies, including atroposelective halogenation, kinetic resolution, condensation–oxidation, and photoredox deracemization, are discussed in detail. In addition, the review provides an in-depth analysis of the applications of various catalytic systems, such as peptide catalysis, enzymatic catalysis, metal catalysis, chiral phosphoric acid catalysis, and others. Despite the substantial progress made thus far, several challenges remain, including the expansion of the substrate scope, enhanced control over stereoselectivity, and further exploration of practical applications, such as drug discovery and asymmetric catalysis. These insights are expected to guide future research towards the development of novel synthetic strategies, the diversification of structural variants, and a comprehensive understanding of their biological activities and catalytic functions. Ultimately, this will foster the continued growth and evolution of this rapidly advancing field. Full article

This research employs 2-methylene-tetrahydronaphtalene-1-ones and N-cyclopropylanilines as starting materials, integrating photocatalysis and organic phosphoric acid catalysis to synthesize 2-amino-spiro[4.5]decane-6-ones via a [3 + 2] cycloaddition approach. This method boasts the advantage of mild reaction conditions that are photocatalyst-free and metal catalyst-free. It achieves 100% atom conversion of the substrates, aligning with the principles of green chemistry. Additionally, it attains a high diastereoselectivity result of up to 99:1, demonstrating good stereoselectivity. In the derivatives of 2-methylene-tetrahydronaphtalene-1-ones, substrates with alkane rings of different sizes or thiophene replacing the phenyl ring are also amenable to this method, enabling the synthesis of different [4.4], [4.5], and [4.6] spirocyclic compounds. In the derivatives of N-cyclopropylanilines, substrates with para-fluoro and meta-fluoro substitutions are also amenable to this method. Finally, a preliminary mechanistic investigation was conducted, proposing a plausible reaction mechanism pathway initiating from the intermediate N-cyclopropylanilines with chiral phosphoric acid. Full article

In this study we report on the efficiency of a furane-indole-chromenone-based organic derivative (FIC) as a photocatalyst in the α-arylation of enol acetate upon LED irradiation at 405 nm, and as a photoinitiator/photocatalyst in the free radical polymerization of an acrylate group in the presence of bis-(4-tert-butylphenyl)iodonium hexafluorophosphate (Iod) as an additive, or in the presence of both Iod and ethyl-4-(dimethyl amino) benzoate (EDB) under LED irradiation at 365 nm. The photochemical properties of this new light-sensitive compound are described, and the wide redox window (3.27 eV) and the high excited-state potentials FIC*/FIC^●− (+2.64 V vs. SCE) and FIC^●+/FIC* (−2.41 V vs. SCE) offered by this photocatalyst are revealed. The chemical mechanisms that govern the radical chemistry are discussed by means of different techniques, including fluorescence-quenching experiments, UV-visible absorption and fluorescence spectroscopy, and cyclic voltammetry analysis. Full article

Photoredox-catalyzed phosphonylation of bromo-substituted 1,10-phenanthrolines under visible light irradiation was studied. The reaction was shown to proceed under mild conditions with Eosin Y as a photocatalyst in DMSO under blue light irradiation. It is transition-metal-free and affords the target phosphonate-substituted 1,10-phenanthrolines in moderate yields (26–51%) in 22 to 40 h. The rate and selectivity of the reaction depend largely on the position of the bromine atom, as well as on the nature and position of other substituents in the 1,10-phenanthroline core. Full article

Porphyrins were identified some years ago as a promising, easily accessible, and tunable class of organic photoredox catalysts, but a systematic study on the effect of the electronic nature and of the position of the substituents on both the ground-state and the excited-state redox potentials of these compounds is still lacking. We prepared a set of known functionalized porphyrin derivatives containing different substituents either in one of the meso positions or at a β-pyrrole carbon, and we determined their ground- and (singlet) excited-state redox potentials. We found that while the estimated singlet excited-state energies are essentially unaffected by the introduction of substituents, the redox potentials (both in the ground- and in the singlet excited-state) depend on the electron-withdrawing or electron-donating nature of the substituents. Thus, the presence of groups with electron-withdrawing resonance effects results in an enhancement of the reduction facility of the photocatalyst, both in the ground and in the excited state. We next prepared a second set of four previously unknown meso-substituted porphyrins, having a benzoyl group at different positions. The reduction facility of the porphyrin increases with the proximity of the substituent to the porphine core, reaching a maximum when the benzoyl substituent is introduced at a meso position. Full article

A new cooperative photoredox catalytic system, [Ru^II(trpy)(bpy)(H₂O)][3,3′-Co(8,9,12-Cl₃-1,2-C₂B₉H₈)₂]₂, 5, has been synthesized and fully characterized for the first time. In this system, the photoredox catalyst [3,3′-Co(8,9,12-Cl₃-1,2-C₂B₉H₈)₂]⁻ [Cl₆-1]⁻, a metallacarborane, and the oxidation catalyst [Ru^II(trpy)(bpy)(H₂O)]²⁺, 2 are linked by non-covalent interactions. This compound, along with the one previously synthesized by us, [Ru^II(trpy)(bpy)(H₂O)][(3,3′-Co(1,2-C₂B₉H₁₁)₂]₂, 4, are the only examples of cooperative molecular photocatalysts in which the catalyst and photosensitizer are not linked by covalent bonds. Both cooperative systems have proven to be efficient photocatalysts for the oxidation of alkenes in water through Proton Coupled Electron Transfer processes (PCETs). Using 0.05 mol% of catalyst 4, total conversion values were achieved after 15 min with moderate selectivity for the corresponding epoxides, which decreases with reaction time, along with the TON values. However, with 0.005 mol% of catalyst, the conversion values are lower, but the selectivity and TON values are higher. This occurs simultaneously with an increase in the amount of the corresponding diol for most of the substrates studied. Photocatalyst 4 acts as a photocatalyst in both the epoxidation of alkenes and their hydroxylation in aqueous medium. The hybrid system 5 shows generally higher conversion values at low loads compared to those obtained with 4 for most of the substrates studied. However, the selectivity values for the corresponding epoxides are lower even after 15 min of reaction. This is likely due to the enhanced oxidizing capacity of Co^IV in catalyst 5, resulting from the presence of more electron-withdrawing substituents on the metallacarborane platform. Full article

A novel and efficient method for functionalizing organosulfones has been established, utilizing a visible-light-driven intermolecular radical cascade cyclization of α-allyl-β-ketosulfones. This process employs fac-Ir(ppy)₃ as the photoredox catalyst and α-carbonyl alkyl bromide as the oxidizing agent. Via this approach, the substrates experience intermolecular addition of α-carbonyl alkyl radicals to the alkene bonds, initiating a sequence of C-C bond formations that culminate in the production of organosulfone derivatives. Notably, this technique features gentle reaction conditions and an exceptional compatibility with a wide array of functional groups, making it a versatile and valuable addition to the field of organic synthesis. Full article

Carbon dioxide is ideal for carboxylation reactions as a renewable and sustainable C1 feedstock and has significant recognition owing to its low cost, non-toxicity, and high abundance. To depreciate the environmental concentration of CO₂, which causes the greenhouse gas effect, developing new catalytic protocols for organic synthesis in CO₂ utilization is of great importance. This review focuses on carboxylation reactions using CO₂ as a C1 feedstock to synthesize value-added functionalized carboxylic acids and their corresponding derivatives via catalytically generated allyl metal intermediates, photoredox catalysis, and electrocatalysis with a focus on recent developments and opportunities in catalyst design for carboxylation reactions. In this article, we describe recent developments in the carboxylation of C–H bonds, alkenes, and alkynes using CO₂ as the C1 source for various reactions under different conditions, as well as the potential direction for the further development of CO₂ utilization in organic synthesis. Full article

Both sulfonyl and phosphorothioate are important privileged structural motifs which are widely presented in pharmaceuticals and agrochemicals. Herein, we describe an efficient approach to synthesizing sulfonyl-containing phosphorothioates by merging photoredox and copper catalysis at room temperature. This protocol is compatible with a wide range of substrates and can be applied to the late-stage modification of complex molecules. Control experiments are conducted to demonstrate the generation of the sulfonyl radical in the transformation. Full article

TiO₂ is one of the most promising heterogeneous photoredox catalysts employed in oxidative pollutant destruction, CO₂ reduction, water splitting, disinfection, solar cell design and organic synthesis. Due to the wide bandgap of TiO₂, visible light energy is not sufficient for its activation, and electron/hole pairs generated upon UV irradiation demonstrate limited selectivity for application in organic synthesis. Thus, the development of TiO₂-based catalytic systems activated by visible light is highly attractive. In the present work we demonstrate the generation of t-BuOO• radicals from tert-butylhydroperoxide catalyzed using commercially available unmodified TiO₂ under visible light. This finding was used for the highly selective CH-peroxidation of barbituric acids, which contrasts with the behavior of the known TiO₂/H₂O₂/UV photocatalytic system used for deep oxidation of organic pollutants. Full article

The functionalisation of C–H bonds has been an enormous achievement in synthetic methodology, enabling new retrosynthetic disconnections and affording simple synthetic equivalents for synthons. Hydrogen atom transfer (HAT) is a key method for forming alkyl radicals from C–H substrates. Classic reactions, including the Barton nitrite ester reaction and Hofmann–Löffler–Freytag reaction, among others, provided early examples of HAT. However, recent developments in photoredox catalysis and electrochemistry have made HAT a powerful synthetic tool capable of introducing a wide range of functional groups into C–H bonds. Moreover, greater mechanistic insights into HAT have stimulated the development of increasingly site-selective protocols. Site-selectivity can be achieved through the tuning of electron density at certain C–H bonds using additives, a judicious choice of HAT reagent, and a solvent system. Herein, we describe the latest methods for functionalizing C–H/Si–H/Ge–H bonds using indirect HAT between 2018–2023, as well as a critical discussion of new HAT reagents, mechanistic aspects, substrate scopes, and background contexts of the protocols. Full article

Triplet-triplet annihilation upconversion (TTA-UC) has considerable potential for emerging applications in bioimaging, optogenetics, photoredox catalysis, solar energy harvesting, etc. Fluoroboron dipyrrole (Bodipy) dyes are an essential type of annihilator in TTA-UC. However, conventional Bodipy dyes generally have large molar extinction coefficients and small Stokes shifts (<20 nm), subjecting them to severe internal filtration effects at high concentrations, and resulting in low upconversion quantum efficiency of TTA-UC systems using Bodipy dyes as annihilators. In this study, a Bodipy dimer (B-2) with large Stokes shifts was synthesized using the strategy of dimerization of an already reported Bodipy annihilator (B-1). Photophysical characterization and theoretical chemical analysis showed that both B-1 and B-2 can couple with the red light-activated photosensitizer PdTPBP to fulfill TTA-UC; however, the higher fluorescence quantum yield of B-2 resulted in a higher upconversion efficiency (η_UC) for PdTPBP/B-2 (10.7%) than for PdTPBP/B-1 (4.0%). This study proposes a new strategy to expand Bodipy Stokes shifts and improve TTA-UC performance, which can facilitate the application of TTA-UC in photonics and biophotonics. Full article