Electron Donor-acceptor Research Articles

Photoactivated Formal [3 + 2]/[4+2] Cycloaddition of N‐Aryl Cyclopropyl and Cyclobutylamines

AbstractOrganic transformations initiated by photochemical activation have been at the forefront of reaction discovery. In this study, we present a formal photochemical [3+2] and [4+2] cycloaddition using N‐aryl cyclopropylamines and N‐aryl cyclobutylamines in conjunction with α,β‐unsaturated carbonyl systems, unveiling two distinct mechanistic pathways. The [3+2] cycloaddition is elucidated as being guided by the photochemical activity of an electron donor‐acceptor (EDA) complex. Simultaneously, intermolecular [4+2] annulation of cyclobutylanilines is achieved by visible‐light photoredox catalysis. These simple methodologies have wide applicability, facilitating the synthesis of N‐arylaminocycloalkyl compounds in yields ranging from good to excellent.

Electron-Donor-Mediated Divergent Transformation of Br-RF via EDA Complex for the Synthesis of Fluorine-Containing Oxindoles and Amides.

We have developed an unprecedented electron-donor-controlled divergent reaction between N-alkylsulfonylated acrylamides and Br-RF, facilitated by an electron donor-acceptor (EDA) complex, for the synthesis of fluorine-containing oxindoles and amides. Key to this divergent transformation is the EDA complex generation by altering electron donors. This approach has several advantages, such as broad substrate scope, being metal-catalyst- and photocatalyst-free, and having good functional group tolerance.

Solvent Dictated Organic Transformations.

Solvent plays an important role in many chemical reactions. The C-H activation has been one of the most powerful tools in organic synthesis. These reactions are often assisted by solvents which not only provide a medium for the chemical reactions but also facilitate reaching to the product stage. The solvent helps the reaction profile both chemically and energetically to reach the targeted product. Organic transformations via C-H activation from the solvent assistance perspective has been discussed in this review. Various solvents such as tetrahydrofuran (THF), MeCN, dichloromethane (DCM), dimethoxyethane (DME), 1,2-dichloroethane (1,2-DCE), dimethylformamide (DMF), dimethylsulfoxide (DMSO), isopropyl nitrile (iPrCN), 1,4-dioxane, AcOH, trifluoroacetic acid (TFA), Ac2O, PhCF3, chloroform (CHCl3), H2O, N-methylpyrrolidone (NMP), acetone, methyl tert-butyl ether (MTBE), toluene, p-xylene, alcohols, MeOH, 1,1,1-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), tert-amyl alcohol and their roles are discussed. The exclusive role of the solvent in various transformations has been deliberated by highlighting the substrate scope, along with the proposed mechanisms. For easy classification, the review has been divided into three parts: (i) solvent-switched divergent C-H activation; (ii) C-H bond activation with solvent as the coupling reagent, and (iii) C-H activation with solvent caging and solvent-assisted electron donor acceptor (EDA) complex formation and autocatalysis.

Visible-light-induced hydrosulfonylation of alkynes driven by electron-donor–acceptor (EDA) complexes

Visible-light-induced hydrosulfonylation of alkynes driven by electron-donor–acceptor (EDA) complexes

Discovery of EDA‐Complex Photochemical Reactions Using Computational Vision

Herein, we report a multidimensional screening strategy to discover Electron Donor‐Acceptor (EDA) complex photochemical reactions using only simple photographic devices, such as webcams or cellphones, combined with TLC analysis. An algorithm was designed to automatically identify EDA‐complex reactive mixtures in solution by processing digital images from a 96‐well microplate, alongside TLC results. The code detects the absorption region of the mixture in the visible spectrum and quantifies color changes through grayscale values. Integrated automatic TLC analysis further classifies mixtures as colorimetric reactions, non‐reactive, or potentially reactive EDA complexes. Leveraging this screening platform, we have developed a new EDA‐mediated approach to synthesize iminophosphoranes in yields up to 90%.

Divergent Synthesis of Benzo[4,5]imidazo[2,1-b][1,3]thiazines and α-Trifluoromethyl-β-arylthio Tertiary Alcohols from 2-Mercaptobenzimidazoles and α-CF3 Alkenes.

An efficient and metal-free approach for the divergent synthesis of 2-fluoro-3-aryl-4H-benzo[4,5]imidazo[2,1-b][1,3]thiazines and α-trifluoromethyl-β-arylthio tertiary alcohols from 2-mercaptoimidazoles and α-CF3 alkenes has been developed. The chemoselectivity was well controlled by base or light; a series of 2-fluoro-3-aryl-4H-benzo[4,5]imidazo[2,1-b][1,3]thiazines were afforded via base-mediated sequential SN2'- and SNV-type reactions. Meanwhile, α-trifluoromethyl-β-arylthio tertiary alcohols could be selectively achieved through visible-light-driven and electron donor-acceptor (EDA) complex-initiated radical cascade thiolation/hydroxylation in the absence of base, transition metal, and external photocatalyst.

Precise Single-Atom Modification of Hybrid Lead Chlorides for Electron Donor-Acceptor Effect and Enhanced Photocatalytic Aerobic Oxidation.

Hybrid lead halides show significant potential in photocatalysis due to their excellent photophysical properties, but the atomically precise modification of their organic component to achieve synergistic interactions with the lead halide units remains a great challenge. Herein, for the first time, we have employed the crystal engineering strategy to construct a class of single-atom-substituted hybrid lead halides with electron donor-acceptor (D-A) effect. The lead halide frameworks consist of 1D linear [PbCl]+ chains as inorganic building units and benzoxadiazole/benzothiadiazole/ benzoselenadiazole-funtionalized dicarboxylates as linkers. The covalent bonding between the organic ligands with electron-withdrawing groups and the electron-rich lead halide units not only facilitate the charge separation, but also enhance structural robustness that is critical for photocatalysis. The D-A structured lead halides serve as highly efficient heterogeneous photooxidation catalysts, including aerobic oxidation of C(sp3)-H bonds, oxidative coupling of primary amines, oxidation of phenylboronic acids and selective oxidation of sulfides that are demonstrated in 30 examples. Importantly, these photooxidation reactions are able to be driven by natural sunlight and ambient air to afford quantitative yields. Moreover, our lead halide photocatalysts are successful to fix into a photocatalytic flow system, which enables the flow-type synthesis of high value-added photooxidation products on a gram scale.

Electron donor-acceptor complex enabled photocascade strategy for the synthesis of trans-dihydrofuro[3,2-c]chromen-4-one scaffolds via radical conjugate addition of pyridinium ylide.

A visible-light-induced photocascade strategy is disclosed for the synthesis of trans-dihydrofuro[3,2-c]chromen-4-one scaffolds. The photocascade consists of electron donor-acceptor (EDA) complex enabled formation of arylidene coumarinone, followed by 1,4-radical conjugate addition (1,4-RCA) of an in situ generated pyridinium ylide radical (PyYR) towards diastereoselective formation of the trans-dihydrofuro[3,2-c]chromen-4-one scaffold in good to excellent yield. Thorough mechanistic investigations comprising photophysical, spectroscopic, electrochemical and DFT studies provide further insights into the reaction mechanism.

Visible-light-promoted direct desulfurization of glycosyl thiols to access C-glycosides

C-Glycosides are essential for the study of biological processes and the development of carbohydrate-based drugs. Despite the tremendous hurdles, glycochemists have often fantasized about the efficient, highly stereoselective synthesis of C-glycosides with the shortest steps under mild conditions. Herein, we report a desulfurative radical protocol to synthesize C-alkyl glycosides and coumarin C-glycosides under visible-light induced conditions without the need of an extra photocatalyst, in which stable and readily available glycosyl thiols that could be readily obtained from native sugars are activated in situ by pentafluoropyridine. The benefits of this procedure include high stereoselectivity, broad substrate scope, and easy handling. Mechanistic studies indicate that the in situ produced tetrafluoropyridyl S-glycosides form key electron donor–acceptor (EDA) complexes with Hantzsch ester (for C-alkyl glycosides) or Et3N (for coumarin C-glycosides), which, upon irradiation with visible light, trigger a cascade of glycosyl radical processes to access C-glycosides smoothly.

Near-Infrared Unimolecular Chemiluminescence Probes for Deep-Tissue Imaging.

Chemiluminescence (CL) imaging has emerged as a promising optical imaging technique due to minimal background autofluorescence and being excitation-free. However, the emission of most chemiluminescent probes was concentrated in the visible light region, which limited the tissue penetration. Although some NIR chemiluminescence probes have been reported based on the chemiluminescence resonance energy transfer (CRET) strategy, the energy loss was inevitable. Thus, it is crucial to develop near-infrared (NIR) unimolecular probes with direct chemiluminescence. Herein, we propose a strategy of increasing conjugation for designing and synthesizing novel NIR chemiluminescence unimolecular probes that consist of luminol, electron acceptor, π-bridge, and electron donor. Luminol was conjugated to the unimolecular backbone to produce direct NIR chemiluminescence. Notably, the direct CL mechanism of probes was investigated. Compared with CRET-based chemiluminescence, this direct CL was more advantageous to immediately convert the chemical energy into chemiluminescence, avoiding energy degradation. Furthermore, the corresponding nanoparticles with great biosafety were prepared by self-assembly with amphiphilic DSPE-PEG. Especially, TTBL@PEG-NPs with NIR-I emission were successfully used in the sensitive in vivo chemiluminescence imaging of various inflammation models, such as peritonitis, ear swelling, and colitis. This study paves the way for the design of NIR unimolecular chemiluminescence probes and deep-tissue imaging.

Unique Electron Donor–Acceptor Complex Conformation Ensures Both the Efficiency and Enantioselectivity of Photoinduced Radical Cyclization in a Non-natural Photoenzyme

Unique Electron Donor–Acceptor Complex Conformation Ensures Both the Efficiency and Enantioselectivity of Photoinduced Radical Cyclization in a Non-natural Photoenzyme

INCLUSION OF AZULENE STRUCTURAL UNITS IN THE BASIS OF CONJUGATED POLYMERS: IMPROVEMENT OF PROTON SENSITIVITY AND FLUORESCENCE

The growing interest in aromatic polymer compounds with an extended π-electron coupling system is explained by their importance as functional materials for organic optoelectronics. At present, much attention is paid to arylated, as well as substituted by electron acceptor and/or electron donor groups, aromatic and heteroaromatic compounds. One of the advantages of such conjugated aromatic systems is that they can fine-tune the electronic structure of materials in order to optimize their performance and morphology. In this regard, the structural isomer of naphthalene - azulene is of considerable interest. The nonalternant aromatic hydrocarbon azulene has unique electronic and spectral properties, including a polarized structure with a dipole moment of the order of 1,08 D and abnormal Anti-Kasha fluorescence S2→S0. The article discusses the synthesis of two fluorene-azulene π-conjugated copolymers using the modern methodology of organic synthesis as the Suzuki − Miyaura -cross−coupling reaction. It was shown that the interaction of 1,3-dibromazulene, as well as 2,7-Bis(3-bromoazulen-1-yl)-9,9-dioctyl-fluorene with 2,2'-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(1,3,2-dioxaborinane) under Suzuki − Miyaura cross-coupling conditions, azulene conjugate copolymers were synthesized: poly[2,7-(9,9-dioctylfluorenyl)-alt-(1ꞌ,3ꞌ - azulenyl)] and poly[1,3-bis(9ꞌ,9ꞌ-dioctylfluoren-2ꞌ-yl)azulenyl]-alt-[1ꞌꞌ,3ꞌꞌ - azulenyl]. It is revealed that neutral solutions of the obtained copolymers are nonfluorescent, but they become luminescent upon addition of trifluoroacetic acid. The «launching» of fluorescence occurs as a result of the formation of a 6 π-electron azulenyl cation, which rearranges the general electronic character of polymers, in particular, HOMO-LUMO levels and band gap. The obtained results demonstrate that the introduction of azulene units into a conjugated polymer framework has great potential for application as new protic functional materials.

Long organic persistent luminescence triggered by photo-induced charge-separation for water-resistant information encryption.

The long persistent luminescence (LPL) phenomenon in the water environment presents us with a broad blueprint to struggle for a new generation of optical materials. However, the realization of water-resistant LPL remains a formidable challenge due to severe quenching of triplet excitons inflowing media. Here, an electron donor-acceptor system is designed based on a B2O3 host and carbon dot (CD) guest, which exhibits deep-blue LPL with a lasting time of about 21 s to the naked eye. The average LPL lifetime is over 2 s, and the LPL quantum yield is 10.78%. This host-guest system possesses charge-separated states and charge-transferred states triggered by an optical source, which is the foundation for LPL. Importantly, in water environments (HCl, NaOH, electrolyte NaCl, and H2O), the LPL of as-obtained CDs@B2O3 can still remain due to high environmental stability of B2O3. Based on the excellent LPL with ultra-long lifetime and water-resistant feature, the CDs@B2O3 successfully applies in water-resistant information encryption.

C(sp2)-Arylsulfones Directly from Arylsulfonyl Chlorides with Boronic Acids by Photoactivation of Boosted EDA Complexes.

Directly with arylsulfonyl chlorides, a green and efficient deborylativesulfonylation of aryl(alkenyl)boronic acids has been developed to access both diarylsulfones and vinylarylsulfones in moderate to excellent yields at room temperature under visible-light irradiation. This protocol features broad C(sp2)-arylsulfone applicability, simple operation, accessibility of raw materials and ease of scale-up. The key to the success of this photoredox transformation is introducing catalytic amounts of additives, naphthalen-2-ols, thus boosting the formed electron donor-acceptor (EDA) complexes, which can dramatically improve not only the reaction efficiency but also the selectivity. This strategywas inspired and derived from specific substrates, representing a rare paradigm of how to exploit a more general reaction system. Moreover, extensive control experiments provide insights into the proposed mechanism.

Visible-light-promoted [3 + 2] cycloaddition for the synthesis of spirooxindoles under external photocatalyst-free conditions

A visible-light-promoted [3 + 2] cycloaddition of 3-alkenylindole-2-ones with 2-mercaptoimidazoles for the construction of diverse imidazo[2,1-b]thiazole fused 3,3′-spirooxindoles has been developed. Mechanism studies have shown that this transformation is initiated through visible-light excitation of 3-alkenylindole-2-ones, rather than an electron donor-acceptor (EDA) complexes-promoted process. In summary, we have successfully developed a method for simultaneously constructing C−N and C−S bonds under visible-light conditions, and synthesized over 40 examples of new nitrogen- and sulfur-containing fused heterocyclic compounds with potential biological activity with a yield of up to 99 %. This method exhibits simple operation, mild reaction conditions, high atom economy, good functional group tolerance and does not require the use of any transition metals and external photocatalysts. Gram-scale reaction further demonstrates the practicality of this protocol.

Dissolved organic matter-mediated adsorption behavior of benzophenones on functionalized covalent triazine frameworks

Adsorption is a highly efficacious technique for the remediation of organic micropollutants (OMPs). However, the presence of dissolved organic matter (DOM) frequently impedes adsorbent process, with insufficient attention given to this influence. This study systematically evaluates the adsorption performance of covalent triazine frameworks (CTFs) functionalized with electron-donating or electron-withdrawing groups for benzophenones (BPs). The adsorption capacities of SO3H-CTF, OH-CTF, and NH2-CTF for BPs were 512.11 μmol/g, 1356.27 μmol/g, and 1421.85 μmol/g, respectively. The adsorption mechanism is predominantly governed by π-π electron donor–acceptor (EDA) interactions, supplemented by hydrogen bonding, particularly in hydroxyl-containing BPs, with electrostatic interactions being relatively negligible. Functionalization with − OH and − NH2 groups increased the electron density in π-conjugated regions, enhancing BPs adsorption capacity, whereas − SO3H modification, due to its electron-withdrawing nature, acted as a π electron acceptor. Importantly, the mediating role of humic acid (HA) in the adsorption process was investigated. The CTF-BPs-HA ternary system can either inhibit/enhance π-π EDA interactions between π-electron donor/acceptor and BPs by adsorbing onto the CTF materials. The HA-mediated system primarily affects the film diffusion stage, with minimal impact on pore diffusion and inner surface adsorption. The oxygenated functional groups in HA slightly enhanced hydrogen bonding within the adsorption system, with negligible influence on electrostatic interactions. In the presence of HA, the overall adsorption capacity of SO3H-CTF decreased by 67.0 %, while that of OH-CTF and NH2-CTF increased by 120.9 % and 55.3 %, respectively. This study elucidates the electronic behavior modifications of functionalized CTFs during BPs adsorption and underscores the significant role of HA in interaction mechanisms, providing theoretical guidance for the design of advanced adsorbents to enhance pollutant removal efficiency.

Construction of Covalent Triazine Frameworks with Electronic Donor-Acceptor System for Efficient Photocatalytic C-H Hydroxylation of Imidazole[1,2-α]Pyridine Derivatives.

Covalent triazine frameworks (CTFs) are promising heterogeneous photocatalyst candidates owing to their excellent stability, conjugacy, and tunability. In this study, a series of CTFs decorated with different substituents (H, MeO, and F) were synthesised and utilised as photocatalysts for C-H activation reactions. The corresponding optoelectronic properties could be precisely regulated by the electronic effects of different substituents in the nanopore channels of the CTFs; these CTFs were effective photocatalysts for C-H activation in organic synthesis due to their unique structures and optoelectronic properties. Methoxy-substituted CTF (MeO-CTF) exhibited extraordinary catalytic performance and reusability in C-H functionalization by constructing an electronic donor-acceptor system, achieving the highest yield in the photocatalytic C3-H hydroxylation of 2-phenylimidazole[1,2-α]pyridine. This strategy provides a new scaffold for the rational design of CTFs as efficient photocatalysts for organic synthesis.

Traceless Nucleophile Strategy for C5-Selective C-H Sulfonylation of Pyridines.

The functionalization of pyridines is crucial for the rapid construction and derivatization of agrochemicals, pharmaceuticals, and materials. Conventional functionalization approaches have primarily focused on the ortho- and para-positions, while achieving precise meta-selective functionalization, particularly at the C5 position in substituted pyridines, remains a formidable challenge due to the intrinsic electronic properties of pyridines. Herein, we present a new strategy for meta- and C5-selective C-H sulfonylation of N-amidopyridinium salts, which employs a transient enamine-type intermediate generated through a nucleophilic addition to N-amidopyridinium salts. This process harnesses the power of electron donor-acceptor complexes, enabling high selectivity and broad applicability, including the construction of complex pyridines bearing valuable sulfonyl functionalities under mild conditions without the need for an external photocatalyst. The remarkable C5 selectivity, combined with the broad applicability to late-stage functionalization, significantly expands the toolbox for pyridine functionalization, unlocking access to previously unattainable meta-sulfonylated pyridines.

Competitive adsorption of oxytetracycline and sulfamethoxazole by nanosized activated carbon in aquatic environments: Experimental analysis and DFT calculations

Nanosized activated carbon (NAC) is an emerging carbonaceous nanomaterial for water treatment, while oxytetracycline (OTC) and sulfamethoxazole (SMX) coexisting in aquatic environments may undergo competitive adsorption to influence its removal efficiency. This study investigated the competitive adsorption of OTC and SMX onto NAC under different interaction sequence, pH, electrolyte, and water matrix conditions, using experimental analysis and density function theory (DFT) calculations. Adsorption kinetics show that increasing concentration of one antibiotic inhibited the adsorption of another. Faster equilibrium was attained in binary systems than single systems due to competitive adsorption, with pseudo-second-order model providing the best fit in both systems. Adsorption isotherms suggest that NAC exhibited stronger affinity towards OTC (395.26 mg/g) than SMX (232.02 mg/g), with Langmuir model showing satisfactory fitting in both single and binary systems. Sequential adsorption of [NAC + OTC] + SMX was more favored than binary adsorption, aligning with the optimum configuration of SMX--[NAC-OTC±] with binding energy of −57.25 kcal/mol from DFT calculations. Competitive adsorption was preferred within pH 3.2–5.6, where electrostatic attraction existed between NAC and cationic antibiotics. Salting-out, charge screening, and complexation effects from Na+ and Ca2+ influenced competitive adsorption. Optimal removal of OTC and SMX by NAC was achieved in wastewater effluent among four water matrices in both single and binary systems. Hydrogen bonding, π − π electron donor–acceptor interactions, electrostatic interactions, and hydrophobic interactions contributed to adsorption. Sequential change in functional groups of NAC followed − OH → C − H → C − O → C = C and C = C → C − O → C − H → − OH in single and binary systems, respectively. The findings provide valuable insights into the competitive adsorption mechanisms of antibiotics on NAC, highlighting its potential for remediating mixtures of antibiotics in complex aquatic environments.

Insight into C4 Selectivity in the Light-Driven C-H Fluoroalkylation of Pyridines and Quinolines.

Given the prevalence of pyridine motifs in FDA-approved drugs, selective fluoroalkylation of pyridines and quinolines is essential for preparing diverse bioisosteres. However, challenges are often faced with conventional Minisci reactions in achieving precise regioselectivity owing to competing reaction sites of pyridine and the limited availability of fluoroalkyl radical sources. Herein, we present a light-driven, C4-selective fluoroalkylation of azines utilizing N-aminopyridinium salts and readily available sulfinates. Our approach employs electron donor-acceptor complexes, achieving highly C4-selective fluoroalkylation under mild conditions without an external photocatalyst. This practical method not only enables the installation of CF2H groups but also allows for the incorporation of CF2-alkyl groups with diverse functional entities, surpassing the limitations of previous methods. The versatility of the radical pathway is further demonstrated through straightforward three-component reactions involving alkenes and [1.1.1]propellane. Detailed experimental and computational studies have elucidated the origins of regioselectivity, providing profound insights into the mechanistic aspects.