Heterocyclization Reagents for Rapid Assembly of N-Fused Heteroarenes from Alkenes

Light-Induced, Cs2CO3 Promoted C-S Cleavage of Heteroaryl Sulfones for Benzyl Heteroarylation of [1.1.1]Propellane

In this study, we developed a light-induced difunctionalization of [1.1.1]propellane with heteroaryl sulfones acting as difunctional reagents, allowing the introduction of alkyl and heteroaryl units across bicyclo[1.1.1]pentane frameworks. It features a broad substrate scope and can be used to functionalize structurally complex natural products. Mechanistic investigations indicate the Cs2CO3 promoted homolytic cleavage of heteroaryl sulfone C-S bonds by light. Moreover, the benzothiazolyl moiety in the products can serve as a formyl precursor, indicating the robust transformability of the products, owing to the ability of aldehydes to undergo a wide variety of organic transformations.

Silver-Promoted Three-Component Synthesis of Perfluoroalkenyl Pyrroles through Partial Defluorinative Functionalization of Perfluoroalkyl Halides

A silver-promoted three-component heterocyclization of alkynes, perfluoroalkyl halides, and 1,3-dinucleophiles was developed for the efficient synthesis of privileged (E)-perfluoroalkenyl pyrroles. The reaction proceeded through a rationally designed sequence of radical perfluoroalkylation and intramolecular defluorinative [3 + 2]-heterocyclization. The utility of perfluoroalkyl halide as a perfluoroalkenyl reagent, by selective and controllable functionalization of two inert C(sp3)-F bonds at vicinal carbon centers on the perfluoroalkyl chain, provides a new reaction mode for the synthesis of value-added organofluorides starting from the easily available and low-cost fluorinated feedstock.

Silver-Catalyzed Decarboxylative Remote Fluorination via a Zwitterion-Promoted 1,4-Heteroaryl Migration

A silver-catalyzed decarboxylative remote fluorination via a zwitterion-promoted 1,4-heteroaryl migration has been developed. A variety of heteroaryl-tethered benzyl fluorides have been readily synthesized with good regioselectivity under mild conditions. The zwitterion of the substrate is suggested to accelerate the 1,4-heteroaryl migration, which determines the regioselectivity of this transformation.

(3+2) Cycloaddition of Heteroaromatic N-Ylides with Sulfenes

A (3+2) cycloaddition of heteroaromatic N-ylides with sulfenes, which are generated in situ from sulfonyl chlorides, has been developed. A variety of ylides were transformed into the corresponding sulfone-embedded N-fused heterocycles in high yields. Hexafluoroisopropyl mesylate was demonstrated to be a suitable reactant for quinolinium ylides. Furthermore, this cycloaddition could be performed with an ylide prepared by a Cu-catalyzed ylide transfer reaction in a one-pot manner, extending the substrate scope to an unisolable ylide.

Overcoming Radical Stability Order via DABCO-Triggered Desulfurization: Visible-Light-Promoted 1,2,4-Trifunctionalization of Butenyl Benzothiazole Sulfone with Thiosulfonate

A radical 1,2,4-trifunctional reaction of thiosulfonate to unactivated olefin is achieved by a migration strategy under mild conditions. In this reaction, the more unstable primary free radicals are in situ generated after the migration of heteroaryl groups in the presence of DABCO. This trifunctionalization of unactivated olefins involves two C-S bond formations and one C-C bond formation.

Photoinduced Copper-Catalyzed Enantioconvergent Remote Alkynylation via 1,4-Heteroaryl Migration

A photoinduced copper-catalyzed enantioconvergent remote alkynylation of N-hydroxyphthalimide esters with terminal alkynes via 1,4-heteroaryl migration has been developed. A broad scope of heteroaryl-tethered chiral alkynes has been synthesized with good regio- and enantioselectivities. The chiral-ligand-coordinated copper species plays a dual role as both the photoredox and cross-coupling catalyst. This methodology provides a new platform for enantioconvergent remote alkynylations.

Multisite-Sequential Cyclization To Construct 1,2,4-Triazole-Based N-Fused Heterocyclics

A feasible protocol that uses atomic groups (KSCN, KSeCN, and NH₂CN), o-bromobenzoyl hydrazides, and formyls as reaction factors to synthesize N-fused 1,2,4-triazole with benzothiazides, benzoselenazinones, and quinazolinones was proposed. The method overcomes the lengthy multistep synthesis, narrow substrate scope, and toxicity challenge induced by the use or production of hazardous substances. It also enables the development of fused-heterocyclic selenium and quinazolinone derivatives. Their fluorescent performance further demonstrates the practicability of this methodology.

Titanium-Mediated aza-Nazarov Annulation for the Synthesis of N-Fused Tricycles: A General Method to Access Lamellarin Analogues

Fused heterocycles with nitrogen incorporation are of particular bioactive use and high importance in many research fields, especially isoquinoline-based [6/6/5] tricycles. Here, we report a unique strategy to access multifunctional N-fused tricycles from α,β-unsaturated isoquinoline ketone and sulfonamide under mild reaction conditions. The methodology features wide substrate tolerance, and a set of N-fused heteroarenes including quinoline, phthalazine, quinazoline, quinoxaline, and benzothiazole cores are furnished efficiently. Moreover, the protocol is easy to scale up to synthesize lamellarin analogues, and the amide group of the product is also easy to transfer to other functional groups.

1,4-Aryl migration in ketene-derived enolates by a polar-radical-crossover cascade

The arylation of carboxylic acid derivatives via Smiles rearrangement has gained great interest in recent years. Both radical and ionic approaches, as well as radical-polar crossover concepts, have been developed. In contrast, a reversed polar-radical crossover approach remains underexplored. Here we report a simple, efficient and scalable method for the preparation of sterically hindered and valuable α-quaternary amides via a polar-radical crossover-enolate oxidation-aryl migration pathway. A variety of easily accessible N-alkyl and N-arylsulfonamides are reacted with disubstituted ketenes to give the corresponding amide enolates, which undergo upon single electron transfer oxidation, a 1,4-aryl migration, desulfonylation, hydrogen atom transfer cascade to provide α-quaternary amides in good to excellent yields. Various mono- and di-substituted heteroatom-containing and polycyclic arenes engage in the aryl migration reaction. Functional group tolerance is excellent and substrates as well as reagents are readily available rendering the method broadly applicable.

The α-arylation of amides via aryl migration has attracted considerable interest in recent years. Here, the authors report a method for the preparation of bulky α-quaternary amides via a polar-radical crossover enolate oxidation-aryl migration cascade.

Base-promoted [4 + 2] annulation of pyrrole-2-carbaldehyde derivatives with β,γ-unsaturated α-ketoesters: syntheses of 5,6-dihydroindolizines

A base-promoted [4 + 2] annulation of pyrrole-2-carbaldehyde derivatives with β,γ-unsaturated α-ketoesters for the syntheses of multisubstituted 5,6-dihydroindolizines was developed.

Radical trifunctionalization of hexenenitrile via remote cyano migration

A novel radical-mediated trifunctionalization of hexenenitriles via the strategy of remote functional group migration is disclosed. A portfolio of functionalized hexenenitriles are employed as substrates. After difunctionalization of the unactivated alkenyl part via remote cyano migration, the in situ formed radical intermediate is captured by an azido radical, thus enabling the trifunctionalization. The reaction features mild conditions and broad functional group compatibility, leading to valuable products bearing multiple useful groups. This protocol further extends the scope of remote functional group migration.

Recent advances in the synthesis of indolizine and its derivatives by radical cyclization/cross-coupling

Indolizine is a nitrogen-containing heterocycle that has a variety of potential biological activities, and some indolizine derivatives with excellent fluorescence properties can even be used as organic fluorescent molecules for biological and material applications. Thus, many approaches for their synthesis have been developed. Among them, radical-induced synthetic approaches are receiving increasing attention owing to their unique advantages, such as efficient heterocycle construction, efficient C-C or C-X bond construction, and high atom- and step-economy. This review systematically examines the current and latest synthetic strategies using radical species or radical intermediates for synthesizing indolizines and their derivatives. This review is classified into two parts based on the type of building blocks used for indolizine ring construction and the type of radical trigger for indolizine derivative construction. We anticipate that this review will provide a deep understanding of this topic, and ultimately help researchers to develop novel approaches for the synthesis of indolizine and its derivatives.

Visible-Light-Triggered Sulfonylation/Aryl Migration/Desulfonylation and C-S/Se Bond Formation Reaction: 1,2,4-Trifunctionalization of Butenyl Benzothiazole Sulfone with Thiosulfonate/Selenosulfonates

A visible-light-triggered radical cascade sulfonylation/aryl migration/desulfonylation and C-S/Se bond formation reaction of butenyl benzothiazole sulfone with thiosulfonates or selenosulfonates is developed. This study affords the 1,2,4-trifunctionalization of butenyl benzothiazole sulfone derivatives under mild conditions.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Radical-mediated rearrangements: past, present, and future

Rearrangement reactions, one of the most significant transformations in organic chemistry, play an irreplaceable role in improving synthetic efficiency and molecular complexity. Concomitant cleavage and reconstruction of chemical bonds can display the great artistry and the glamour of synthetic chemistry. Over the past century, ionic rearrangement reactions, in particular those involving cationic pathways, have represented most of the research. Alongside the renaissance of radical chemistry, radical-mediated rearrangements have recently seen a rapid increase of attention from the chemical community. Many new radical rearrangements that extensively reveal the migratory behaviour of functional groups have been unveiled in the last decade. This Review provides a comprehensive perspective on the area from the past to present achievements, and brings up the prospects that may inspire colleagues to develop more useful synthetic tools based on radical rearrangements.

Copper-catalyzed [3 + 2]/[3 + 2] carboannulation of dienynes and arylsulfonyl chlorides enabled by Smiles rearrangement: access to cyclopenta[a]indene-fused quinolinones

A radical Smiles rearrangement strategy for allowing an unprecedented [3 + 2]/[3 + 2] carboannulation of dienynes with arylsulfonyl chlorides using cheap copper catalysis is described.

Radical heteroarylation of unactivated remote C(sp3)–H bonds via intramolecular heteroaryl migration

Described herein is the radical-mediated heteroarylation of unactivated remote C(sp3)–H bonds via intramolecular heteroaryl migration.