Electron Donor-acceptor Complexes Research Articles

Multicomponent Synthesis of Alkyl BCP-Heteroaryls via Electron Donor-Acceptor Complex Photoactivation under Mild Conditions.

In the vanguard of sustainable chemistry, the pursuit of efficient pathways for the synthesis of alkyl bicyclo[1.1.1]pentane-heteroaryls has captured the attention of the scientific vanguard. We herein report a groundbreaking and eco-conscious multicomponent coupling reaction that paves the way for the alkylation and heteroarylation of [1.1.1]propellane, a process uniquely enabled by the photochemical prowess of an electron donor-acceptor (EDA) complex. This method is distinguished by its minimalist yet powerful approach: devoid of transition metals, additives, and photosensitizers. Its universality is further exemplified by the seamless compatibility of a broad spectrum of alkyl halides and heteroarenes under standardized conditions, heralding a new era of synthetic versatility. The method's practicality is underscored by its capacity for late-stage modification of pharmaceuticals, offering a transformative tool for the enhancement of existing drug molecules. Moreover, the facile derivatization of the synthesized products underscores the method's adaptability and potential for diverse applications. Our mechanistic studies have elucidated the underlying radical-relay pathway, pinpointing the pivotal role of the EDA complex in initiating the transformation. This discovery not only enriches our fundamental understanding of the reaction but also opens avenues for strategic optimization.

Bis(dialkylaminethiocarbonyl)disulfides Act as Electron Acceptors for EDA Complexes for the Synthesis of Dithiocarbamate Derivatives under Visible Light.

This study proposes a green and efficient atom- and step-economical method for converting hazardous CS2 to dithiocarbamate derivatives under visible light irradiation and catalyst-free conditions. By the construction of novel C-S and C-N bonds, a series of β-dicarbonyl compounds and amines are incorporated into the products. Under light, CS2 and amine first form bis(dialkylaminethiocarbonyl)disulfides, which then react with K2CO3-activated β-dicarbonyl compounds to form electron donor-acceptor (EDA) complexes and subsequently generate the target products. This study confirms for the first time that bis(dialkylaminethiocarbonyl)disulfides can act as electron acceptors to form an EDA complex with β-dicarbonyl compounds, which are then coupled to form the target product under light.

Visible light-induced PPh3/MI-promoted δ-C(sp3)-H chlorination and cyclization with N-chloro-arylsulfonamides via EDA complexes.

Triphenylphosphine, iodide and N-chloro-arylsulfonamides could generate amidyl radicals via EDA (Electron Donor-Acceptor) complexes under visible light irradiation, and this strategy enables the synthesis of valuable δ-chloro-arylsulfonamide and N-arylsulfonylpyrrolidine motifs in moderate yields. This blue LED-induced method utilizes more readily available reagents, providing advantages in terms of cost efficiency, broad substrate scope, and functional-group compatibility.

Visible-light-promoted azidation/arylation of unactivated alkenes with Togni-N3via electron donor-acceptor complexes.

A visible-light-promoted azidation/arylation of unactivated alkenes with Togni-N3 has been achieved, leading to a series of azidated pyrrolo[1,2-a]indoles under photocatalyst-free conditions. Notably, an EDA complex derived from the electron-rich indole derivatives and Togni-N3 served as the key intermediate in this reaction.

Photoinduced Radical Relay Reaction of 2-Methylthiolated Phenylacetylenes/Alkynones Initiated by Electron Donor-Acceptor Complexes.

A method was found to construct sulfur-containing five- and six-membered heterocyclic alkyl sulfonyl compounds by using visible light and free radicals activated and/or generated by EDA complexes/homolytic cleavage as initiators to stimulate the relay reaction of alkynes/alkynones. This method puts forward a new strategy to initiate alkyl sulfonation of alkynes/alkynones with only a catalytic amount of the initiator. This strategy of generating the initiator by EDA complex activation/homolytic cleavage provides a new idea for the following substances that must be excited.

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.

Nickel-Catalyzed Asymmetric Synthesis of β- or β,γ-Substituted GABA Derivatives Enabled by Photoactive Ternary Electron Donor–Acceptor Complex

Nickel-Catalyzed Asymmetric Synthesis of β- or β,γ-Substituted GABA Derivatives Enabled by Photoactive Ternary Electron Donor–Acceptor Complex

Organophotocatalytic Reduction of Benzenes to Cyclohexenes.

The reduction of abundant benzene rings to scarce C(sp3)-rich motifs is invaluable for drug design, as C(sp3) content is known to correlate with clinical success. Cyclohexenes are attractive targets, as they can be rapidly elaborated into large product libraries and are stable against rearomatization. However, partial reduction reactions of benzenes to cyclohexenes are rare and have a very narrow scope. Herein we report a broadly applicable method that converts electron-poor benzenes to cyclohexenes and tolerates Lewis-basic functional groups such as triazoles and thioethers as well as reducible groups such as cyanides, alkynes, and sulfones. The reaction utilizes an organic donor that induces mild arene reduction by preassociation to a photoexcitable electron donor-acceptor (EDA) complex and mild isomerization of redox-inert 1,4-cyclohexadienes to reducible 1,3-cyclohexadienes without a strong base in its oxidized thioquinone methide form.

Visible-Light-Induced Divergent Oxygenation of Methylbenzene Utilizing Aryl Halides.

The selective oxidation of methylbenzene to value-added products is of indisputable importance in organic synthesis. Although photocatalytic oxidation reactions of toluene have achieved great success for the preparation of its oxidative products, such as carboxylic acids, benzaldehyde, and benzoate, there remains a lack of a unified photocatalytic system for the selective preparation of these oxidation products. Herein, we report a metal- and additive-free photocatalytic protocol enabled by aryl halides using O2 as a green oxidant for the selective synthesis of the above-mentioned three oxidation products by adjusting the reaction solvent. This strategy features many advantages, including environmentally friendly and mild reaction conditions, broad substrate applicability and functional group tolerance, and potential practical application for the synthesis of aromatic carboxylic drugs and polymer materials and degradation of polystyrene waste. The continuous-flow system was utilized for the oxidation of toluene, which resulted in a reduced reaction time and increased production efficiency. Detailed mechanistic investigation revealed that the hydrogen atom transfer process was facilitated by the bromine radical from aryl halides for further oxidation, and an electron donor-acceptor complex of methylbenzene and aryl halides may exist.

Electron Donor-Acceptor Complex-Driven Divergent Routes to α-Amino Bicyclopentyl Iodides and Methylene Cyclobutanols.

Amines are essential due to their structural diversity and biological significance. Introducing the valuable bicyclopentane (BCP) moiety at the α-position of amines offers a promising strategy for developing novel bioactive compounds. This study outlines a divergent synthesis approach to generate α-amino-functionalized bicyclopentyl iodides and methylene cyclobutanols under mild and environmentally sustainable conditions. By employing an electron donor-acceptor (EDA) complex between amine and the inexpensive and readily available inorganic base Cs2CO3, this method circumvents the need for strongly reducing, metal-based photocatalysts typically required for aryl radical generation. This approach enables the α-functionalization of various aliphatic and alicyclic amines via a 1,5-hydrogen atom transfer mechanism.

Photoredox-Catalyzed C-H Methylation of N-Heteroarenes Enabled by N,N-Dimethylethanolamine.

A visible-light-driven radical C-H methylation of N-heteroarenes that is efficient and additive- and catalyst-free and employs readily available N,N-dimethylethanolamine as the methyl source has been developed. The transformation offers the benefits of broad substrate scope, mild reaction conditions, and operational simplicity. A photoactive electron donor-acceptor (EDA) complex between N-heteroarenes and N,N-dimethylethanolamine is essential for this transformation, as revealed by mechanistic investigations.

Photoinduced EDA Complex-Initiated Synthesis of Fluoroalkylated Isoquinolinonediones.

A visible-light-induced radical tandem difluoroalkylation/cyclization to construct CF2-containing isoquinolinonedione skeletons with methacryloyl benzamides is developed. Broad substrate scopes are compatible with metal-, oxidant- and photocatalyst-free conditions under room temperature in good-to-excellent yields. Mechanistic analysis revealed that the transformation is initiated by photoinduced electron donor-acceptor (EDA) complexes formation.

Visible light induced reactions of quinones

AbstractThis review covers the visible light induced reactions of quinones such as benzoquinone, naphthoquinone, and anthraquinone. These quinones are distinguished by their fully conjugated structures, which feature minimal energy gaps, and nonbonding electron pairs on the oxygen atoms. Such structural attributes facilitate np → π* transition, allowing for easy access to excited states and rendering quinones highly reactive under visible‐light irradiation. We describe three primary types of reactions facilitated by these electronic characteristics: Paternò–Büchi (PB) reactions, which entail [2 + 2] photocycloaddition between the carbonyl groups of quinones and alkenes or alkynes; CH activation processes, which showcase quinones' versatility in functionalizing hydrocarbons; and the formation of electron donor–acceptor complexes, demonstrating quinones' capability to engage in charge transfer interactions. Through this review, we highlight the critical role quinones play in photochemistry, their unique electronic properties, and their broad applicability in synthetic organic chemistry.

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

The method toward the vinyl sulfones has been realized by visible-light-induced hydrosulfonylation of alkynes via an EDA process. DIPEA was used as both electron donor for EDA complex and hydrogen donor for hydrogen atom transfer.

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.

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.

Electron Donor-Acceptor Complex-Assisted Photochemical Conversion of O-2-Nitrobenzyl Protected Hydroxamates to Amides.

The hydroxamic acid functionality is present in various medicinal agents and has attracted special interest for synthetic transformations in both organic and medicinal chemistry. The N-O bond cleavage of hydroxamic acid derivatives provides an interesting transformation for the generation of various products. We demonstrate, herein, that O-benzyl-type protected hydroxamic acids may undergo photochemical N-O bond cleavage, in the presence or absence of a catalyst, leading to amides. Although some O-benzyl protected aromatic hydroxamates may be photochemically converted to amides in the presence of a base and anthracene as the catalyst, employing O-2-nitrobenzyl group allowed the smooth conversion of both aliphatic and aromatic hydroxamates to primary or secondary amides in good to excellent yields in the presence of an amine, bypassing the need of a catalyst. DFT and UV-Vis studies supported the effective generation of an electron donor-acceptor (EDA) complex between O-2-nitrobenzyl hydroxamates and amines, which enabled the successful product formation under these photochemical conditions. An extensive substrate scope was demonstrated, showcasing that both aliphatic and aromatic hydroxamates are compatible with this protocol, affording a wide variety of primary and secondary amides.

Electron Donor-Acceptor Complex-Enabled Autoinductive Conversion of Acylnitromethanes to Acylnitrile Oxides in a Photochemical Machetti-De Sarlo Reaction: Synthesis of 5-Substituted 3-Acylisoxazoles.

A photochemical Machetti-De Sarlo reaction has been developed for preparing 5-substituted 3-acylisoxazoles from acylnitromethanes and terminal alkynes. This photochemical protocol utilizes an innovative electron donor-acceptor complex, generated in situ from acylnitromethanes, catalytic LiOtBu, and 1,1,1,3,3,3-hexafluoro-2-propanol, as a photosensitizer to promote rapid conversion with a broad substrate scope in up to 80% efficiency. A sigmoidal autoinductive kinetic profile is revealed, demonstrating the novel and unique dual catalysis in the first photochemical approach of this reaction.

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%.

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