Selective C(sp2)-H bond functionalization of olefins via visible-light-induced photoredox-quinuclidine dual catalysis

The site selective C(sp²)-H bond functionalization of olefins has been achieved through a visible-light-induced photoredox-quinuclidine dual catalysis upon merging the quinuclidinium radical cation addition to alkene strategy and the distal heteroaryl ipso-migration strategy. This synthetic protocol features a simple operation with readily available starting materials in good step-economy to access alkenylheteroaromatic products in moderate to good yields under mild conditions. A plausible cascade catalytic reaction mechanism is also proposed.

Electrochemical alkene azidocyanation via 1,4-nitrile migration

An electrochemical method for the azidocyanation of alkenes via 1,4-nitrile migration has been developed. This organic oxidant free method is applicable across various alkene containing cyanohydrins, and provides access to a broad range of synthetically useful 1,2-azidonitriles (28 examples). This methodology was extended to an electrochemical alkene sulfonylcyanation procedure, as well as to access a trifunctionalized hexanenitrile from a malononitrile starting material. The orthogonal derivatization of the products was also demonstrated through chemoselective transformations.

Radical Heteroarylation of Alkenes and Alkanes via Heteroaryl Migration

Heteroarenes are important units in organic chemistry and are ubiquitous in natural products, pharmaceuticals, and numerous artificial molecules. Despite great efforts devoted to accessing heteroarenes, the development of new methods to efficiently produce heteroarenes remains a long-term interest. Recently, the strategy of radical-mediated heteroaryl migration has supplied a robust toolkit for the synthesis of a diversity of heteroaryl-containing compounds. This Account summarizes our recent achievements in this field and provides insight into the incorporation of heteroarenes into organic skeletons.

Copper-catalyzed oxidative phosphonoheteroarylation of alkenes with phosphonates and N-heteroarenes via P–H/C–H functionalization

Copper-catalyzed oxidative phosphonoheteroarylation of alkenes with phosphonates and nucleophilic N-heteroarenes via P–H/C–H functionalization is depicted.

Multisubstituted Cyclohexene Construction through Telescoped Radical-Addition Induced Remote Functional Group Migration and Horner-Wadsworth-Emmons (HWE) Olefination

An efficient telescoped method for the rapid assembly of multisubstituted cyclohexenes is presented herein. The whole process nicely merges photoredox-promoted alkene difunctionalization via remote functional group migration with concomitant intramolecular Horner-Wadsworth-Emmons (HWE) olefination. The characteristic feature of this protocol resides in the fact that the follow-up requiring ketone functionality for ring-closing olefination is in situ unveiled from the otherwise inert tertiary alcohol by the preceding alkene difunctionalization.

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.

Visible-light-facilitated P-center radical addition to C[double bond, length as m-dash]X (X = C, N) bonds results in cyclizations

Visible-light-facilitated phosphorus radical reactions have been developed as a powerful and sustainable tool for the synthesis of various organophosphorus compounds. In general, these reactions require stoichiometric amounts of oxidants, and reductants, bases, and radical initiators, leading to uneconomical and complicated processes. Progress has been made over the past few years toward using reactions that proceed under eco-benign and mild reaction conditions. Furthermore, these reactions have broad functional group tolerance, with some facile and economical pathways. Herein, we summarize the discoveries and achievements pertaining to C-P bond formation through a visible light photocatalysis procedure with high atom economy, made by our group and other research groups. It was established that greener and more environmentally friendly approaches do not require an additional oxidant or base. Moreover, we have designed and synthesized a new type of P-radical precursor, which can take part in reactions without the requirement for any additional bases, oxidants, and additives. This breakthrough, pertaining to novel visible-light-induced transformations, will be discussed and a plausible mechanism is proposed, based on corresponding experiments and the literature.

Trifluoromethanesulfonyl azide as a bifunctional reagent for metal-free azidotrifluoromethylation of unactivated alkenes

Vicinal trifluoromethyl azides have widespread applications in organic synthesis and drug development. However, their preparation is generally limited to transition-metal-catalyzed three-component reactions. We report here a simple and metal-free method that rapidly provides these building blocks from abundant alkenes and trifluoromethanesulfonyl azide (N₃SO₂CF₃). This unprecedented two-component reaction employs readily available N₃SO₂CF₃ as a bifunctional reagent to concurrently incorporate both CF₃ and N₃ groups, which avoids the use of their expensive and low atom economic precursors. A wide range of functional groups, including bio-relevant heterocycles and amino acids, were tolerated. Application of this method was further demonstrated by scale-up synthesis (5 mmol), product derivatization to CF₃-containing medicinal chemistry motifs, as well as late-stage modification of natural product and drug derivatives.

A two-component and metal-free azidotrifluoromethylation of alkenes is realized using readily synthesized trifluoromethanesulfonyl azide (N₃SO₂CF₃) as a bifunctional reagent for both CF₃ and N₃ groups.

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.

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.

Difunctionalization of Alkenes and Alkynes via Intermolecular Radical and Nucleophilic Additions

Popular and readily available alkenes and alkynes are good substrates for the preparation of functionalized molecules through radical and/or ionic addition reactions. Difunctionalization is a topic of current interest due to its high efficiency, substrate versatility, and operational simplicity. Presented in this article are radical addition followed by oxidation and nucleophilic addition reactions for difunctionalization of alkenes or alkynes. The difunctionalization could be accomplished through 1,2-addition (vicinal) and 1,n-addition (distal or remote) if H-atom or group-transfer is involved in the reaction process. A wide range of moieties, such as alkyl (R), perfluoroalkyl (R_f), aryl (Ar), hydroxy (OH), alkoxy (OR), acetatic (O₂CR), halogenic (X), amino (NR₂), azido (N₃), cyano (CN), as well as sulfur- and phosphorous-containing groups can be incorporated through the difunctionalization reactions. Radicals generated from peroxides or single electron transfer (SET) agents, under photoredox or electrochemical reactions are employed for the reactions.

Radical-Mediated Remote Functional Group Migration

Alkenes are ubiquitous in natural products and are extensively used as synthetic feedstocks in multiple fields including organic synthesis, medicinal chemistry, and materials science. Radical-mediated difunctionalization of alkenes provides a powerful tactic for alkene utilization. Despite the considerable progress made in the past several decades, state-of-the-art methods are highly dependent upon activated alkenes in which a proximal group with a π-electron system (e.g., aryl, carbonyl, and heteroatom) is requisite to stabilize the nascent alkyl radical intermediate via p-π conjugation or p orbitals of the heteroatom. In contrast, the transformation of unactivated alkenes, such as aliphatic alkenes, remains challenging.To overcome this obstacle, we have recently disclosed the strategy of intramolecular distal functional group migration (FGM), which has been efficiently applied in radical difunctionalization of unactivated alkenes. A portfolio of functional groups, such as cyano, heteroaryl, oximino, formyl, and alkynyl groups, showcase the excellent migratory aptitude. Mechanistically, after the addition of an extrinsic radical to the alkene, the newly formed active alkyl radical is rapidly captured by the intramolecular migratory group to generate a cyclic intermediate. Subsequent cleavage of the cyclic C-C bond of the intermediate leads to the functionalized product through the FGM process. Based on the strategy of FGM, a set of elusive difunctionalizations of unactivated alkenes have been accomplished (Part A).Alongside this research, an upgraded highly efficient synthetic strategy, "dock-migration," is created for intermolecular difunctionalization of alkenes. A diversity of sulfone-based dual-function reagents are developed. The intermolecular transformation is initiated by docking the dual-function reagent to the alkene, followed by intramolecular migration of the functional group. Compared to the original FGM protocol, the scope of alkenes is significantly extended from the strategically placed tertiary alcohol-substituted alkenes to general alkenes. Both activated and unactivated alkenes are well tolerated. By this approach, radical-mediated fluoroalkylheteroarylation, fluoroalkylalkynylation, and alkylation of alkenes have been achieved (Part B).Direct elaboration of C-H bonds into the targeted functional groups represents one of the most ideal and straightforward methods for molecular functionalization. The FGM strategy proves to be an ingenious tool for radical-mediated functionalization of remote unactivated C(sp³)-H bonds. Based on the FGM process, we have accomplished: (a) remote C(sp³)-H heteroarylation and cyanation of unprotected alcohols via the cascade of alkoxy radical-enabled hydrogen atom transfer (HAT) and intramolecular functional group (e.g., heteroaryl, cyano) migration, and (b) distal C(sp³)-H vinylation of propargylic alcohols through consecutive alkenyl radical-promoted HAT process and subsequent alkenyl migration (Part C).

C- to N-Center Remote Heteroaryl Migration via Electrochemical Initiation of N Radical by Organic Catalyst

Herein an exogenous oxidant- and metal-free electrochemical heteroaryl migration triggered by N radicals to construct new N-C bonds was developed. This methodology features a high atom economy and utilization rate of energy, and it is insensitive to water and air. Moreover, a user-friendly undivided cell was employed. The use of an organic catalyst makes it more efficient, green, and practical.

Iron-catalyzed acylation-functionalization of unactivated alkenes with aldehydes

Herein, an iron-catalyzed acylation-functionalization of unactivated alkenes with aldehydes via distal group ipso-migration is reported.

Aromatization-driven deconstruction/refunctionalization of unstrained rings

Aromatization-driven ring-opening/functionalization of common unstrained rings has been developed with the in situ generation of pre-aromatic fused spiro heterocycles as the key step.

Visible-light-promoted N-centered radical generation for remote heteroaryl migration

An efficient visible-light-mediated organocatalyzed N–H heteroarylation was accomplished via remote heteroaryl ipso-migration.

Proton-Coupled Electron Transfer Enables Tandem Radical Relay for Asymmetric Copper-Catalyzed Phosphinoylcyanation of Styrenes

A tandem radical relay strategy was realized for the first Cu(I)-catalyzed enantioselective phosphinocyanation of styrenes. In this reaction, ^tBuOOSiMe₃ generated in situ from ^tBuOOH serves as a radical initiator to trigger t-butoxy radical production upon oxidization of L*Cu(I) species via proton-coupled-electron transfer (PCET) pathway, which leads to sequential phosphinoyl radical and benzyl radical formations. The resultant β-cyanodiarylphosphine oxides could be easily converted to a series of chiral γ-amino phosphine ligands.

Cleavage of carbon–carbon bonds by radical reactions

This review provides insights into the in situ generated radicals triggered carbon–carbon bond cleavage reactions.

Intramolecular nitration–aminocarbonylation of unactivated olefins: metal-free synthesis of γ-lactams

A novel, metal-free synthesis of valuable γ-lactams through the radical-mediated nitration–aminocarbonylation of unactivated olefins is reported.

Iron(iii)-catalyzed radical α,β-aminophosphinoylation of styrenes with diphenylphosphine oxides and anilines

A Fe-catalyzed highly regioselective α,β-difunctionalization of vinylarenes with diphenylphosphine oxides and anilines is disclosed, in which α,β-aminophosphinoylation is efficiently and conveniently constructed with good functional compatibility and a broad substrate scope.