Copper-Mediated Oxidative Radical Addition/Cyclization Cascade: Synthesis of Trifluoromethylated and Sulfonated Quinoline-2,4(1H,3H)-diones

Visible-light-induced photocatalyst-free cascade cyclization of 3-(2-(ethynyl)phenyl)quinazolinones to sulfonated quinolino[2,1-b]quinazolinones

A visible-light-induced K2S2O8-promoted cascade sulfonation/cyclization reaction was established using 3-(2-(ethynyl)phenyl)quinazolinones as efficient substrates under mild conditions. A series of sulfonated quinolino[2,1-b]quinazolinones were successfully synthesized under transition-metal- and photocatalyst-free conditions. Notably, this strategy has the advantages of room temperature and simple operation, easy scale-up, and good functional group tolerance.

Visible-Light-Induced Cascade Cyclization of 1-Acryloyl-2-cyanoindole: Access of Difluoroalkylated Pyrrolo[1,2-a]indolediones

An effective method for accessing diverse difluoroalkylated pyrrolo[1,2-a]indolediones via visible-light-induced PhI(OAc)2-promoted cascade difluoroalkylation/cyclization reaction under mild conditions has been established. This method is noteworthy for its use of DMSO-H2O as a green medium at room temperature and avoidance of photocatalysts. The reactions are straightforward to execute and convenient to expand on, provide good to excellent yields, and have good functional group tolerance.

Visible-Light-Promoted Cascade Cyclization of 3-Ethynyl-[1,1'-biphenyl]-2-Carbonitriles with Unsaturated α-Bromocarbonyls

A visible-light-promoted cascade cyclization of 3-ethynyl-[1,1'-biphenyl]-2-carbonitriles with unsaturated α-bromocarbonyls for the synthesis of tetrahydrobenzo[mn]cyclopenta[b]acridines is described. Three C(sp3)-C(sp2) bonds, one C(sp2)-N bond, and three cycles can be formed in a single reaction through the addition of a C-centered radical to the carbon-carbon triple bond and three radical cyclizations. This reaction features mild conditions, wide substrate scope, and high bond-forming efficiency.

Cascade Cyclizations Triggered by Photochemically Generated Carbamoyl Radicals Derived from Alkyl Amines

We report on a visible light-mediated cascade carbamoylation/cyclization of acrylamides using dihydropyridyl carbamoyl donors derived from alkyl amines. Diversely selected acrylamides including 2-cyano-N-arylacrylamides, indolyl- and benzimidazolyl acrylamides, and 2-alkynyl-N-aryl acrylamides participate in this reaction, providing products in good yields. The highlights of this photochemical method include the application of alkyl amine-derived carbamoyl donors, peroxide-free reaction conditions, and a broad scope.

Divergent Construction of Azaheterocycles via Alkoxyl Radical-Triggered C-C Bond Cleavage/Cyclization of N-Functionalized Acrylamides

An array of redox-neutral alkylation/cyclization cascade reactions of N-functionalized acrylamides with cycloalkyl hydroperoxides were achieved via the alkoxyl radical-triggered C-C bond cleavage. Through adjusting the radical acceptors on the N atom, a variety of keto-alkylated chain-containing azaheterocycles, including indolo[2,1-a]isoquinolin-6(5H)-ones, quinoline-2,4-diones, and pyrido[4,3,2-gh]phenanthridines were constructed by a one-pot procedure with good yields and excellent functional group tolerance.

Visible-Light-Promoted Phosphorylation/Cyclization of 1-Acryloyl-2-cyanoindoles in Green Solvent

A visible-light-induced persulfate-promoted cascade phosphorylation/cyclization reaction to access various phosphorylated pyrrolo[1,2-a]indolediones under mild conditions was developed. Notably, the transformation was carried out with diethyl carbonate/H₂O as a green medium at room temperature. More impressively, traditional metal catalysts and photocatalysts could be effectively avoided. The reactions are simple to operate, easy to scale up, and have good functional group tolerance.

Cyclization/hydrolysis of 1,5-enenitriles initiated by sulfonyl radicals in the aqueous phase in the presence of the I2/TBHP system

A novel cyclization/hydrolysis of 1,5-enenitriles for the synthesis of valuable pyrrolidine-2,4-diones in the aqueous phase using I₂ as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant is reported. In the presence of the I₂/TBHP system, sulfonyl hydrazides produce sulfonyl radicals, which undergo radical addition, intramolecular cyclization, hydrogen abstraction, and hydrolysis to give the final products. The use of the inexpensive and environmentally friendly I₂/TBHP catalytic oxidation system in the aqueous phase makes it a benign and sustainable strategy.

Free Radical Cascade Carbochloromethylations of Activated Alkenes

Free radical carbochloromethylations of ortho-cyanoarylacrylamides and N-(arylsulfonyl)acrylamides have been developed by employing simple alkyl chlorides as the chloromethyl source. The transformations are characterized by wide functional group compatibility and utilizing readily available reagents, thus providing efficient methods for constructing polychloromethyl-substituted quinoline-2,4-diones and α-aryl-β-polychloromethylated amides.

Complementary Copper-Catalyzed and Electrochemical Aminosulfonylation of O-Homoallyl Benzimidates and N-Alkenyl Amidines with Sodium Sulfinates

A complementary copper-catalyzed and electrochemical aminosulfonylation of O-homoallyl benzimidates and N-alkenyl amidines with sodium sulfinates was developed. The terminal alkene substrate produced sulfone-containing 1,3-oxazines and tetrahydropyrimidines in the presence of Cu(OAc)₂, Ag₂CO₃, and DPP, and under similar reaction conditions, sulfonylated tetrahydro-1,3-oxazepines were prepared from 1-aryl-substituted O-homoallyl benzimidates in moderate to good yields. For certain electron-rich 1,1-diaryl-substituted alkene substrates, the corresponding tetrahydro-1,3-oxazepines could also be obtained in similar or even higher yields via a green electrochemical technique.

Copper-catalyzed switchable cyclization of alkyne-tethered α-bromocarbonyls: selective access to quinolin-2-ones and quinoline-2,4-diones

Copper-catalyzed cyclization of alkynes has played a significant role in modern catalytic chemistry.

Copper-Catalyzed Aminosulfonylation of O-Homoallyl Benzimidates with Sodium Sulfinates to Access Sulfonylated 1,3-Oxazines

A facile copper-catalyzed aminosulfonylation of O-homoallyl benzimidates with sodium sulfinates in the presence of tert-butyl peroxybenzoate (TBPB) and XPhos ligand has been developed. By using this protocol, a variety of potentially bioactive 1,3-oxazines were directly synthesized. This method has the merits of a cheap catalyst, easily available and stable sulfone reagents, and simple operation.

Radical Annulation of 2-Cyanoaryl Acrylamides via C═C Double Bond Cleavage: Access to Amino-Substituted 2-Quinolones

A novel annulation of 2-cyanoaryl acrylamides via C═C double bond cleavage has been developed for facile and efficient access to a broad spectrum of functionalized 4-amino-2-quinolones, which are important N-heterocycles. In this transformation, the solvent THF is demonstrated to play a crucial role, and the addition of alkyl radicals to nitrile, 1,5-hydride shift, and cleavage of the C-C bond are involved in the mechanism.

Synthesis and applications of sodium sulfinates (RSO2Na): a powerful building block for the synthesis of organosulfur compounds

This review highlights the preparation of sodium sulfinates (RSO2Na) and their multifaceted synthetic applications. Substantial progress has been made over the last decade in the utilization of sodium sulfinates emerging as sulfonylating, sulfenylating or sulfinylating reagents, depending on reaction conditions. Sodium sulfinates act as versatile building blocks for preparing many valuable organosulfur compounds through S-S, N-S, and C-S bond-forming reactions. Remarkable advancement has been made in synthesizing thiosulfonates, sulfonamides, sulfides, and sulfones, including vinyl sulfones, allyl sulfones, and β-keto sulfones. The significant achievement of developing sulfonyl radical-triggered ring-closing sulfonylation and multicomponent reactions is also thoroughly discussed. Of note, the most promising site-selective C-H sulfonylation, photoredox catalytic transformations and electrochemical synthesis of sodium sulfinates are also demonstrated. Holistically, this review provides a unique and comprehensive overview of sodium sulfinates, which summarizes 355 core references up to March 2020. The chemistry of sodium sulfinate salts is divided into several sections based on the classes of sulfur-containing compounds with some critical mechanistic insights that are also disclosed.

The Three-Component Synthesis of 4-Sulfonyl-1,2,3-triazoles via a Sequential Aerobic Copper-Catalyzed Sulfonylation and Dimroth Cyclization

4-Sulfonyl-1,2,3-triazole scaffolds possess promising bioactivities and applications as anion binders. However, these structures remain relatively unexplored and efficient synthetic procedures for their synthesis remain desirable. A practical room-temperature, aerobic copper-catalyzed three-component reaction of aromatic ketones, sodium sulfinates, and azides is reported. This procedure allows for facile access to 4-sulfonyl-1,5-disubstituted-1,2,3-triazoles in yields ranging from 34 to 89%. The reaction proceeds via a sequential aerobic copper(II)chloride-catalyzed oxidative sulfonylation and the Dimroth azide–enolate cycloaddition.

Nitriles as radical acceptors in radical cascade reactions

The application of the cyano group as a radical acceptor in the cascade reactions for the construction of various important heterocycles and carbocycles was summarized.

Visible light induced radical cascade cyclization of ortho-cyanoarylacrylamides with phosphine oxides for the preparation of phosphorylated quinoline-2,4(1H,3H)-dione

Visible light induced cascade cyclization of ortho-cyanoarylacrylamides with phosphine oxides for the preparation of phosphorylated quinoline-2,4(1H,3H)-dione was presented. Products with moderate to good yields were efficiently isolated.

Radical Transformations towards the Synthesis of Quinoline: A Review

Quinoline is considered one of the most ubiquitous heterocycles due to its engaging biological activities and synthetic utility over organic transformations. Over the past few decades, numerous reports have been documented in the synthesis of quinolines. The classical methods including, Skraup, Friedlander, Doebner-von-Miller, Conrad-Limpach, Pfitzinger quinoline synthesis, and so forth, these are the well-known methods to construct principal quinoline scaffold with several advantages and limitations. Recently, radical insertion or catalyzed reactions have emerged as a powerful and efficient tool to construct heterocycles with high atom efficiency and step economy. In this concern, this minireview mainly focused on the developments of Quinoline synthesis via radical reactions. In addition, a brief description of the preparation procedure, reactivity, and mechanisms is also included, where as possible. Respectively, the synthesis of quinolines is classified and summarized based on its reactivity, so it will help the researchers to grab the information in this exploration area, as Quinolines are promising pharmacophores.

Oxidative cascade cyclization of 2-cyano-3-arylaniline derived acrylamides with toluenes, ethers, aliphatic alcohols or simple alkanes

Oxidative radical cascade cyclization of 2-cyano-3-arylaniline derived acrylamides with a variety of hydrocarbons including toluenes, ethers, aliphatic alcohols and alkanes has been developed to construct alkyl substituted pyridophenanthridines.

Synthesis of Sulfonylated Lactams by Copper-Mediated Aminosulfonylation of 2-Vinylbenzamides with Sodium Sulfinates

Treatment of 2-vinylbenzamide derivatives with sulfinate sodium in the presence of Cu(NO₃)₂·3H₂O led to an intra/intermolecular aminosulfonylation reaction to produce sulfonylated lactams in moderate to good yields. The developed method features the easily available and stable sulfone reagents, ease of operation, and a broad functional group tolerance.

Metal-Free Radical [2 + 2 + 1] Cyclization of ortho-Cyanoarylacrylamides with Alkyl Nitriles: Synthesis of Pyrrolo[3,2- c]quinolines

A novel radical [2 + 2 + 1] cyclization of ortho-cyanoarylacrylamides with dual α-C-H bonds in alkyl nitriles has been developed. The reaction provides new facile and straightforward access to cyano-substituted pyrrolo[3,2- c]quinolines, which are important nitrogen-containing polyheterocycles. A possible mechanism for the transformation is proposed.

Synthesis of difluoromethylated 2-oxindoles and quinoline-2,4-diones via visible light-induced tandem radical cyclization of N-arylacrylamides

Visible light-induced difluoromethylation of N-arylacrylamides to afford difluoromethylated 2-oxindoles and quinoline-2,4-diones with difluoromethyl 2-pyridyl sulfones as radical precursors has been disclosed.

Copper(i) reagent-promoted hydroxytrifluoromethylation of enamides: flexible synthesis of substituted-3-hydroxy-2-aryl-3-(2,2,2-trifluoro-1-arylethyl)isoindolin-1-one

A novel CuBr-catalyzed hydroxytrifluoromethylation reaction was investigated. Substituted 3-benzylidene-2-arylisoindolin-1-ones was reacted with sodium trifluoromethanesulfinate to afford substituted-3-hydroxy-2-aryl-3-(2,2,2-trifluoro-1-arylethyl)isoindolin-1-one. The reaction proceeded at 25 °C in air atmosphere in the absence of base and ligands. Our results indicate that trifluoromethyl free radical tends to attack a double bond rather than aryl in this reaction.

Copper-Catalyzed Decarboxylative Disulfonylation of Alkynyl Carboxylic Acids with Sulfinic Acids

A copper-catalyzed decarboxylative disulfonylation of alkynyl carboxylic acids with sulfinic acids in aqueous solution has been developed. The reaction provides a straightforward and practical access to (E)-1,2-disulfonylethenes, which are important building blocks in synthetic organic chemistry, and exhibits a good functional group tolerance and excellent stereoselectivity. A possible mechanism for the transformation is proposed.

Oxidative radical cascade cyclization involving C(sp3)–C(sp3), C(sp3)–C(sp2) and C(sp2)–N bonds formation: direct construction of cyano and methyl substituted polyheterocycles

Oxidative radical cascade cyclizations of 2-cyano-3-arylaniline derived acrylamides with acetonitrile and tert-butyl peroxybenzoate have been developed to construct cyano and methyl substituted pyrido[4,3,2-gh]phenanthridines.

An access to 1,3-azasiline-fused quinolinonesviaoxidative heteroannulation involving silyl C(sp3)–H functionalization

A Mn-promoted intermolecular oxidative heteroannulation ofN-(2-cyanoaryl)-acrylamides with tertiary silanes toward 1,3-azasiline-fused quinolinones is presented.

Visible-light-induced oxidant and metal-free dehydrogenative cascade trifluoromethylation and oxidation of 1,6-enynes with water

Generally, oxy-trifluoromethylation in olefins is achieved using oxidants and transition metal catalysts. However, labile olefins remain unexplored due to their incompatibility with harsh reaction conditions. Here, unprecedented light-induced oxidant and metal-free tandem radical cyclization-trifluoromethylation and dehydrogenative oxygenation of 1,6-enynes have been achieved using a photoredox catalyst, CF3SO2Na, and phenanthrene-9,10-dione (PQ), Langlois' reagent (CF3SO2Na) and water as the oxygen source. This benign protocol allows for access to various CF3-containing C3-aryloyl/acylated benzofurans, benzothiophenes, and indoles. Moreover, the oxidized undesired products, which are inherently formed by the cleavage of the vinylic carbon and heteroatom bond, have been circumvented under oxidant free conditions. The mechanistic investigations by UV-visible and ESR spectroscopy, electrochemical studies, isotope labelling and density functional theory (DFT) suggest that light induced PQ produced a CF3 radical from CF3SO2Na. The generated CF3 radical adds to the alkene, followed by cyclization, to provide a vinylic radical that transfers an electron to PQ and generates a vinylic cation. Alternatively, electron transfer may occur from the CF3-added alkene moiety, forming a carbocation, which would undergo cationic cyclization to generate a vinylic carbocation. The subsequent addition of water to the vinylic cation, followed by the elimination of hydrogen gas, led to the formation of trifluoromethylated C3-aryloyl/acylated heterocycles.

Photoredox Catalysis: Construction of Polyheterocycles via Alkoxycarbonylation/Addition/Cyclization Sequence

A novel visible-light-induced cascade reaction for the preparation of ester-functionalized polyheterocycles was developed under metal-free conditions, which was initiated by an intermolecular radical addition to a carbon-carbon double bond of N-arylacrylamide derivatives using alkyl carbazate as the ester source followed by cyano-mediated cyclization. The desired phenanthridine derivative products were isolated in moderate to high yields with broad substrate scope.

Palladium-catalyzed tandem cyclization/sulfonylation of homoallenyl amides with sodium sulfinates

A palladium-catalyzed cyclizative sulfonylation of homoallenyl amides has been developed using sodium sulfinates as the sulfonylation reagent and PhI(O₂CCF₃)₂ as the oxidant, providing a facile access to 2-amino-5-sulfonylmethylfurans in good to excellent yields.

Copper-catalyzed oxidative dehydrogenative coupling of carboxylic acids with H-phosphonates: an efficient and practical approach to acyl phosphate esters

A practical method through a copper-catalyzed dehydrogenative coupling of carboxylic acids with H-phosphonates to construct acyl phosphate esters has been developed.

Metal-free sequential decarbonylative annulation of N-cyanamides for the construction of 2,3-dihydropyrrolo[2,1-b]quinazolin-9(1H)-ones

A convenient metal-free sequential decarbonylative annulation of unactivated alkenes for the construction of quinazolinones and dihydroisoquinolinones has been developed.

Silver-mediated radical 5-exo-dig cyclization of 2-alkynylbenzonitriles: synthesis of phosphinylated 1-indenones

A new silver-mediated 5-exo-dig cyclization of 2-alkynylbenzonitriles with disubstituted phosphine oxide and H₂O has been developed.