Photocatalytic difunctionalization of arylalkenes with quinoxalinones and dialkyl dithiophosphoric acids

Here, a photocatalytic three-component reaction between arylalkenes, quinoxalinones and dialkyl dithiophosphoric acids was developed. This protocol allows the simultaneous incorporation of heterocyclic and dithiophosphoryl groups into a single molecule structure efficiently. These functionalities are important precursors in medicinal chemistry.

Visible-light-induced tandem reaction of quinoxalin-2(1H)-ones, alkenes, and sulfonyl chlorides

A visible-light-induced tandem reaction involving quinoxalin-2(1H)-ones, alkenes, and sulfonyl chlorides, catalyzed by 4CzIPN, was developed. The utilization of easily accessible sulfonyl chlorides, metal-free conditions, and a wide substrate scope established this protocol as an efficient and alternative method for obtaining sulfonated quinoxalin-2(1H)-ones.

Generation and Application of Aryl Radicals Under Photoinduced Conditions

Photoinduced aryl radical generation is a powerful strategy in organic synthesis that facilitates the formation of diverse carbon-carbon and carbon-heteroatom bonds. The synthetic applications of photoinduced aryl radical formation in the synthesis of complex organic compounds, including natural products, physiologically significant molecules, and functional materials, have received immense attention. An overview of current developments in photoinduced aryl radical production methods and their uses in organic synthesis is given in this article. A generalized idea of how to choose the reagents and approach for the generation of aryl radicals is described, along with photoinduced techniques and associated mechanistic insights. Overall, this article offers a critical assessment of the mechanistic results as well as the selection of reaction parameters for specific reagents in the context of radical cascades, cross-coupling reactions, aryl radical functionalization, and selective C-H functionalization of aryl substrates.

Arylthianthrenium Salts as the Aryl Sources: Visible Light/Copper Catalysis-Enabled Intermolecular Azidosulfonylation of Alkenes

The difunctionalization of alkenes using aryl thianthrenium salts as the aryl sources has been reported sporadically. However, the four-component difunctionalization of alkenes on the basis of aryl thianthrenium salts has not been reported thus far and still remains a challenge. Herein, a visible light/copper catalysis-enabled four-component reaction of aryl thianthrenium salts, DABCO·(SO2)2, alkenes, and TMSN3 is presented, which affords a facile approach to β-azidosulfones in good yields with broad substrate scope and excellent functional group tolerance. This strategy indirectly realizes the method for the synthesis of β-azidosulfones through site-selective aryl C-H bond functionalization and alkene difunctionalization. This developed method is an important complement to thianthrenium salts chemistry.

Enantioselective Chemodivergent Three-Component Radical Tandem Reactions through Asymmetric Photoredox Catalysis

Chemodivergent synthesis has been achieved in asymmetric photocatalysis. Under a dual catalyst system consisting of a chiral phosphoric acid and DPZ as a photosensitizer, different inorganic bases enabled the formation of two sets of valuable products from the three-component radical tandem transformations of 2-bromo-1-arylenthan-1-ones, styrenes, and quinoxalin-2(1H)-ones. The key to success was the distinct pKa environment, in which the radicals that formed on the quinoxalin-2(1H)-one rings after two radical addition processes underwent either single-electron oxidation or single-electron reduction. In addition, this work represents the first use of quinoxalin-2(1H)-ones in asymmetric photoredox catalysis.

Metal-Free Photoredox Four-Component Strategy to 1,3-Functionalized BCP Derivatives

Trifluoromethyl bicyclo[1.1.1]pentanes (BCPs) have attracted significant attention from the scientific community and pharmaceutical industries due to their advantageous physicochemical properties as arene bioisosteres. Initial photoredox perfluoroalkylation of [1.1.1]propellane triggers the tandem reaction to the perfluoroalkyl BCP radical followed by Giese addition to an in situ generated electron-deficient alkene by Knoevenagel condensation in a four-component fashion to form 1,3-functionalized BCPs. This strategy provides easy access to various 1,3-functionalized perfluoroalkyl BCP derivatives with the added advantage of nitrile group as a functional handle to diversified transformations. This methodology offers scalability and late-stage derivatization of drug molecules with high chemoselectivity.

A visible-light-mediated cascade reaction of quinoxalin-2(1H)-ones, alkenes, and sulfinic acids

A photocatalytic three-component cascade reaction of quinoxalin-2(1H)-ones, alkenes, and sulfinic acids under metal-, strong oxidant-, and external photocatalyst-free conditions was developed. The reaction was performed at room temperature using air as a green oxidant. Various sulfonated quinoxalin-2(1H)-ones were obtained in satisfactory yields with good functional group compatibility. The preliminary study showed that the current transformation was enabled by the formation of an electron donor-acceptor (EDA) complex between quinoxalin-2(1H)-ones and sulfinic acids.

Recent Developments in Direct C–H Functionalization of Quinoxalin-2(1H)-Ones via Multi-Component Tandem Reactions

The direct C–H multifunctionalization of quinoxalin-2(1H)-ones via multicomponent reactions has attracted considerable interest due to their diverse biological activities and chemical profile. This review will focus on recent achievements. It mainly covers reaction methods for the simultaneous introduction of C–C bonds and C–RF/C/O/N/Cl/S/D bonds into quinoxalin-2(1H)-ones and their reaction mechanisms. Meanwhile, future developments of multi-component reactions of quinoxalin-2(1H)-ones are envisaged, such as the simultaneous construction of C–C and C–B/SI/P/F/I/SE bonds through multi-component reactions; the construction of fused ring and macrocyclic compounds; asymmetric synthesis; green chemistry; bionic structures and other fields. The aim is to enrich the methods for the reaction of quinoxalin-2(1H)-ones at the C3 position, which have rich applications in materials chemistry and pharmaceutical pharmacology.

Radical Fluorosulfonyl Heteroarylation of Unactivated Alkenes with Quinoxalin-2(1H)-ones and Related N-Heterocycles

The incorporation of sulfonyl fluoride groups into molecules has been proved effective to enhance their biological activities or introduce new functions. Herein, we report a transition-metal-free and visible-light-mediated radical 1-fluorosulfonyl-2-heteroarylation of alkenes, which could allow access to a series of SO₂F-containing quinoxalin-2(1H)-ones, which are a critical structural motif widely present in a number of biologically active molecules. Further application of the method to the modification of other heterocycles and drug molecules as well as ligation chemistry via SuFEx click reactions is also demonstrated.

Visible/solar-light-driven thiyl-radical-triggered synthesis of multi-substituted pyridines

A light-triggered synthesis of thio-functionalized pyridines is demonstrated using γ-ketodinitriles, thiols, and eosin Y as the photocatalyst. The reaction proceeds via the selective attack on one of the cyano groups by an in situ generated thiyl radical. The reaction also proceeds with nearly equal efficiency using direct sunlight. Large-scale synthesis and a few useful synthetic transformations of the substituted pyridines are also performed.

Nickel-Catalyzed Three-Component Tandem Radical Cyclization 1,5-Difunctionalization of 1,3-Enynes and Alkyl Bromide

A nickel-catalyzed three-component tandem radical cyclization reaction of aryl bromides with 1,3-enynes and aryl boric acids to construct γ-lactam-substituted allene derivatives has been described. This protocol provides lactam alkyl radicals through the free radical cyclization process, which can be effectively used to participate in the subsequent multicomponent coupling reaction so that 1,3-enynes could directly convert into corresponding poly-substituted allene compounds. In addition, this efficient method enjoys a broad substrate scope and provides a series of 1,5-difunctionalized allenes in a one-pot reaction.

Phototriggered Self-Catalyzed Three-Component Minisci Reaction: A Route to β-C(sp3) Heteroarylated Alcohols/Ethers

Herein, a visible-light-triggered photocatalyst-free radical cascade Minisci reaction of heteroarenes, alkenes, and water/alcohols to obtain diverse β-C(sp³) heteroarylated alcohols/ethers has been developed. Achieved under mild and simple conditions, this protocol is scalable and features broad substrate scope and functional group tolerance. Mechanistic studies demonstrate that the heteroarene can be served as a photocatalyst to engage single-electron transfer with persulfate.

Visible-Light-Mediated Three-Component Cascade Sulfonylative Annulation

Visible-light-promoted cascade radical cyclization for the synthesis of sulfonylated benzimidazo/indolo[2,1-a]iso-quinolin-6(5H)-ones has been reported. The reaction provides transition-metal-free and expeditious access to sulfonylated polyaromatics. The use of sodium metabisulfite as a SO₂ surrogate and the rapid generation of molecular complexity using a three-component photochemical protocol are the salient features of this reaction manifold.

Three-component synthesis of arylsulfonyl-substituted indolo[2,1-a]isoquinolinones and benzimidazo-[2,1-a]isoquinolin-6(5H)-ones by SO2 insertion and radical cascade cyclization

An efficient arylsulfonylation/cyclization of 2-aryl-N-methacryloyl indoles with potassium metabisulfite and aryldiazonium tetrafluoroborates was developed. A series of variously substituted arylsulfonyl indolo[2,1-a]isoquinolin-6(5H)-ones were formed in moderate to good yields via utilization of the nature abundant inorganic salt potassium metabisulfite as a SO₂ surrogate. Additionally, this three-component protocol can also be employed for the synthesis of arylsulfonyl-substituted benzimidazo-[2,1-a]isoquinolin-6(5H)-ones.

Phenanthrenequinone (PQ) catalyzed cross-dehydrogenative coupling of alkanes with quinoxalin-2(1H)-ones and simple N-heteroarenes under visible light irradiation

A direct and convenient strategy to 3-alkylquinoxalin-2(1H)-ones and other alkyl N-heteroarenes via a photocatalyzed alkylation of quinoxalin-2(1H)-ones and other N-heterocycles with commercially available, low-cost alkanes under ambient conditions using phenanthrenequinone (PQ) as a photocatalyst was developed. This transformation has advantages of environment-friendly protocol, mild conditions, good functional-group tolerance, and high yields of products.

Multicomponent reactions and photo/electrochemistry join forces: atom economy meets energy efficiency

Visible-light photoredox catalysis has been regarded as an extremely powerful tool in organic chemistry, bringing the spotlight back to radical processes. The versatility of photocatalyzed reactions has already been demonstrated to be effective in providing alternative routes for cross-coupling as well as multicomponent reactions. The photocatalyst allows the generation of high-energy intermediates through light irradiation rather than using highly reactive reagents or harsh reaction conditions. In a similar vein, organic electrochemistry has experienced a fruitful renaissance as a tool for generating reactive intermediates without the need for any catalyst. Such milder approaches pose the basis toward higher selectivity and broader applicability. In photocatalyzed and electrochemical multicomponent reactions, the generation of the radical species acts as a starter of the cascade of events. This allows for diverse reactivity and the use of reagents is usually not covered by classical methods. Owing to the availability of cheaper and more standardized photo- and electrochemical reactors, as well as easily scalable flow-setups, it is not surprising that these two fields have become areas of increased research interest. Keeping these in view, this review is aimed at providing an overview of the synthetic approaches in the design of MCRs involving photoredox catalysis and/or electrochemical activation as a crucial step with particular focus on the choice of the difunctionalized reagent.

Construction of sulfonated spiro[5,5]trienones from sulfur dioxide via iron-catalyzed dearomative spirocyclization of biaryls

An iron-catalyzed dearomative spirocyclization of biaryl ynones with sodium metabisulfite and cycloketone oxime esters is developed. By using sodium metabisulfite as the source of sulfur dioxide, this approach enables the...

Metal-free three-component cyanoalkylation of quinoxalin-2(1H)-ones with vinylarenes and azobis(alkylcarbonitrile)s

A K2S2O8-mediated C3 cyanoalkylation of quinoxalin-2(1H)-ones via a three-component radical cascade reaction with vinylarenes and azobis(alkylcarbonitrile)s has been achieved.

Construction of 6H-benzo[c]thiochromenes via a tandem reaction of arynes with thionoesters

A mild and transition-metal free method has been proposed for the synthesis of 6H-benzo[c]thiochromenes via the tandem reactions of arynes with thionoesters.