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

Iodine-Promoted Sulfoximidation of Cinnamic Acids via Oxidative C═C Bond Cleavage

An iodine-promoted C═C bond cleavage with concomitant decarboxylation and cross-coupling between cinnamic acids and NH-sulfoximines has been developed. This reaction proceeds via selective C═C bond cleavage, followed by decarboxylation and oxidative sulfoximidation. This metal- and base-free protocol involves dioxygen as the source of oxygen, which is facilitated by tert-butyl hydroperoxide (TBHP) as the oxidant affording N-aroylated sulfoximines with good functional group tolerance and good yields.

Demethylenative cyclization of 1,7-enynes using α-amino radicals as a traceless initiator enabled by Cu(I)-photosensitizers

A rare type of demethylenative intramolecular cyclization of 1,7-enynes to access quinoline-2-(1H)-ones has been successfully developed under the catalysis of P/N-heteroleptic Cu(I)-photosensitizers. Preliminary mechanistic experiments revealed that the key to the success of this protocol lay in the α-amino radical addition-triggered tandem process of intramolecular radical cyclization/1,5-HAT/β-fragmentation. This protocol provides a new avenue for the deconstructive cyclization of alkene derivatives.

Selective Reduction of Triple Bond via Proton-Coupled Electron Transfer for the Synthesis of α,β-Unsaturated γ-Lactams

Described herein is the development of a visible-light-induced photoredox 1,6-enyne reductive cyclization via selective reduction of a triple bond instead of an activated double bond. The selective 1,6-enyne radical cyclization/carbon═carbon double bond cleavage provided a straightforward route to structurally valuable α,β-unsaturated γ-lactams. TEMPO-trap experiments, control experiments, and DFT calculations have offered evidence supporting the possible catalytic cycle.

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.

Visible-Light-Promoted Cyanoalkylation/Cyclization Cascade Reaction to Assemble Polyheterocycles in Continuous Flow

This study describes a visible-light-induced cascade reaction for preparing cyanoalkyl-containing polyheterocycles initiated by the photoinduced radical cascade addition of N-arylacrylamide derivatives using cyclic oxime esters as radical sources followed by cyanoalkyl-mediated cyclization. This protocol features outstanding functional group compatibility, providing a variety of desired phenanthridine derivatives in moderate to good yields. Moreover, the application of a microflow technique enhanced these reactions compared with the equivalent batch reaction, significantly reducing reaction times to 10 min.

Metal- and Base-Free Radical Cascade Cyclization/Hydrolysis of CN-Containing 1,6-Enynes with Ethers to Access Polyheterocycles

A convenient and straightforward approach for the radical cascade cyclization/hydrolysis of CN-containing 1,6-enynes with simple ethers under metal- and base-free conditions is described. This strategy provides a variety of valuable ethers-substituted polyheterocycles via the construction of three C-C bonds, one C=O bond, and two new six-membered rings within a single procedure. The resulting products can smoothly undergo follow-up conversions to various useful scaffolds. The methodology shows excellent functional group tolerance, high step- and atom- economy, and mild reaction conditions, which can be further scaled up to gram quantity in a satisfactory yield.

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.

Iodine-Mediated C═C Double Bond Cleavage toward Pyrido[2,1-b]quinazolinones

A transition-metal-free C═C double bond cleavage reaction employing molecular iodine is described. In the presence of K₂CO₃ as the base, I₂-mediated C═C bond cleavage followed by intramolecular annulation of N-(2-vinylaryl)pyridin-2-amine substrates produces pyrido[2,1-b]quinazolinones and related heterocyclic compounds. This reaction can be completed on a gram scale and has been successfully applied to the synthesis of compounds with important biological properties, including efflux pump inhibitory and antiallergic activities.

Silver-catalyzed decarboxylative radical relay difluoroalkylation–carbocyclization: convenient access to CF2-containing quinolinones

A practical Ag-catalyzed formal decarboxylation and radical difluoroalkylation–carbocyclization–hydrolysis route is established to construct a series of structurally diverse CF2-containing N-heterocycles.