Radical-mediated difunctionalization of unactivated alkenes through distal migration of functional groups

Radical-Mediated Trifunctionalization Reactions

Synthetic radicals have intrinsic power for cascading and multifunctional reactions to construct diverse molecular scaffolds. In the previous review series, we covered 1,2-difunctionalizations, remote 1,3-, 1,4-, 1,5-, 1,6-, and 1,7-difunctionalizations, addition followed by cyclization reactions, and cycloaddition-initiated difunctionalizations. Presented in this paper are radical addition-initiated trifunctionalization reactions of alkenes, alkynes, and their derivatives. After the initial radical addition, there are different pathways, such as group or hydrogen atom transfer, cyclization, and radical coupling, to complete the second and third functionalizations.

Decennary Update on Oxidative-Rearrangement Involving 1,2-Aryl C-C Migration Around Alkenes: Synthetic and Mechanistic Insights

In recent years, numerous methodologies on oxidative rearrangements of alkenes have been investigated, that produce multipurpose synthons and heterocyclic scaffolds of potential applications. The present review focused on recently established methodologies for oxidative transformation via 1,2-aryl migration in alkenes (2013-2023). Special emphasis has been placed on mechanistic pathways to understand the reactivity pattern of different substrates, challenges to enhance selectivity, the key role of different reagents, and effect of different substituents, and how they affect the rearrangement process. Moreover, synthetic limitations and future direction also have been discussed. We believe, this review offers new synthetic and mechanistic insight to develop elegant precursors and approaches to explore the utilization of alkene-based compounds for natural product synthesis and functional materials.

Silylation and (Hetero)aryl/alkenylation of Unactivated Alkenes via Radical-Mediated Distal 1,4-Migration with Hydrosilanes under Organophotocatalysis

We report a novel organic photoredox catalysis to achieve unprecedented γ-(hetero)aryl/alkenyl-δ-silyl aliphatic amines via silyl-mediated distal (hetero)aryl/alkenyl migration of aromatic/alkenyl amines bearing unactivated alkenes with hydrosilanes. This protocol features mild and metal-free reaction conditions, high atom economy, excellent selectivity, and functional group compatibility. Mechanistic studies suggest that silylation and (hetero)aryl/alkenylation involve photoredox hydrogen atom transfer catalysis and subsequent 1,4-migration of a remote (hetero)aryl/alkenyl group from nitrogen to carbon.

E-Selective Radical Difunctionalization of Unactivated Alkynes: Preparation of Functionalized Allyl Alcohols from Aliphatic Alkynes

Radical difunctionalization of aliphatic alkynes provides direct access to valuable multi-substituted alkenes, but achieving a high level of chemo- and stereo-control remains a formidable challenge. Herein a novel photoredox neutral alkyne di-functionalization is reported through functional group migration followed by a radical-polar crossover and energy transfer-enabled stereoconvergent isomerization of alkenes. In this sequence, a hydroxyalkyl and an aryl group are incorporated concomitantly into an alkyne, leading to diversely functionalized E-allyl alcohols. The scope of alkynes is noteworthy, and the reaction tolerates aliphatic alkynes containing hydrogen donating C─H bonds that are prone to intramolecular hydrogen atom transfer. The protocol features broad functional group compatibility, high product diversity, and exclusive chemo- and stereoselectivity, thus providing a practical strategy for the elusive radical di-functionalization of unactivated alkynes.

Modular access to alkylgermanes via reductive germylative alkylation of activated olefins under nickel catalysis

Carbon-introducing difunctionalization of C-C double bonds enabled by transition-metal catalysis is one of most straightforward and efficient strategies to construct C-C and C-X bonds concurrently from readily available feedstocks towards structurally diverse molecules in one step; however, analogous difunctionalization for introducing germanium group and other functionalities remains elusive. Herein, we describe a nickel-catalyzed germylative alkylation of activated olefins with easily accessible primary, secondary and tertiary alkyl bromides and chlorogermanes as the electrophiles to form C-Ge and C-Calkyl bonds simultaneously. This method provides a modular and facile approach for the synthesis of a broad range of alkylgermanes with good functional group compatibility, and can be further applied to the late-stage modification of natural products and pharmaceuticals, as well as ligation of drug fragments. More importantly, this platform enables the expedient synthesis of germanium substituted ospemifene-Ge-OH, which shows improved properties compared to ospemifene in the treatment of breast cancer cells, demonstrating high potential of our protocol in drug development.

Three-Component Photochemical 1,2,5-Trifunctionalizations of Alkenes toward Densely Functionalized Lynchpins

Radical remote 1,n-difunctionalization reactions (n > 2) of alkenes are powerful tools to efficiently introduce functional groups with selected distances into target molecules. Among these reactions, 1,5-difunctionalizations are an important subclass, leading to sought-after scaffolds, but typically suffer from tailored starting materials and strict limitations for the formed functional group in 2-position. Seeking to address these issues and to make radical 1,5-difunctionalizations of alkenes more applicable, we report a novel three-component 1,2,5-trifunctionalization reaction between imine-based bifunctional reagents and two distinct alkenes, driven by visible light energy transfer-catalysis. Key to achieving this selective one-step installation of three different functional groups via the choreographed formation of four bonds was the utilization of a 1,2-boron shift and the rigorous capitalization of radical polarities and stabilities. Thorough mechanistic studies were carried out, and the synthetic utility of the obtained products was demonstrated by various downstream modifications. Notably, in addition to the functionalization of individual functional groups, their interplay gave rise to a unique array of cyclic products.

Free Radicals in the Queue: Selective Successive Addition of Azide and N-Oxyl Radicals to Alkenes

The selective successive addition of azide (•N3) and N-oxyl radicals to alkenes is demonstrated, despite each of the two radicals being known to attack C═C bonds and the mixture of radical adducts possibly being expected. The proposed radical mechanism was supported by density functional theory calculations, electron paramagnetic resonance, and radical trapping experiments. The reaction proceeds at room temperature with the available reagents: NaN3, N-hydroxy compounds, and PhI(OAc)2 as the oxidant. The method can be applied for N-hydroxyimides, N-hydroxyamides, N-hydroxybenzotriazole, and oximes as N-oxyl radical precursors. Vinylarenes, aliphatic alkenes, and even electron-deficient methyl methacrylate were successfully functionalized.

Chemo-divergent Cyano Group Migration: Involving Elimination and Substitution of the Key α-Thianthrenium Cyano Species

Herein, we report a light-driven, radical-type cyano migration in the absence of a photocatalyst, enabling a chemo-divergent synthesis of (Z)-alkenyl nitriles and ketones. Trifluoromethyl thianthrenium salt (TT-CF3+OTf-) plays multiple roles: (a) absorbing light to generate trifluoromethyl radicals to initiate the reaction and (b) forming α-thianthrenium cyano species by in situ capture of TT• +. (Z)-Alkenyl nitriles were formed through the elimination of thianthrenium salts, and aryl ketones were obtained via the nucleophilic substitution of thianthrenium salts.

Merging Fluorine Incorporation and Functional Group Migration

Fluorine incorporation by concomitant fluoroalkyl radical addition to alkene or alkyne and functional group migration (FGM) represents an ingenious and robust strategy for the synthesis of structurally diverse fluorinated compounds. This account gives an overview of related studies in our group, in which three main reaction modes are discussed: 1) radical fluoroalkylative difunctionalization of unactivated alkenes via intramolecular FGM; 2) alkene difunctionalization by docking-migration process using fluoroalkyl-containing bifunctional reagents; 3) incorporation of fluoroalkyl group into C(sp3 )-H bond via consecutive hydrogen atom transfer (HAT) and FGM. Relying on these methods, a variety of trifluoromethylation and di-/mono-fluoroalkylation reactions along with the migration of cyano, heteroaryl, oximino, formyl, alkynyl, and alkenyl groups have been accomplished under mild conditions.

gem-Bromonitroalkane Involved Radical 1,2-Aryl Migration of α,α-Diaryl Allyl Alcohol TMS Ether via Visible-Light Photoredox Catalysis

A mild and efficient coupling method concerning the reactions of gem-bromonitroalkanes with α,α-diaryl allyl alcohol trimethylsilyl ethers was reported. A cascade consisting of visible-light-induced generation of an α-nitroalkyl radical and a subsequent neophyl-type rearrangement was key to realize the coupling reactions. Structurally diverse α-aryl-γ-nitro ketones, especially those bearing a nitrocyclobutyl structure, were prepared in moderate to high yields, which could be converted into spirocyclic nitrones and imines.

Highly Selective Radical Relay 1,4-Oxyimination of Two Electronically Differentiated Olefins

Radical addition reactions of olefins have emerged as an attractive tool for the rapid assembly of complex structures, and have plentiful applications in organic synthesis, however, such reactions are often limited to polymerization or 1,2-difunctionalization. Herein, we disclose an unprecedented radical relay 1,4-oxyimination of two electronically differentiated olefins with a class of bifunctional oxime carbonate reagents via an energy transfer strategy. The protocol is highly chemo- and regioselective, and three different chemical bonds (C-O, C-C, and C-N bonds) were formed in a single operation in an orchestrated manner. Notably, this reaction provides rapid access to a large variety of structurally diverse 1,4-oxyimination products, and the obtained products could be easily converted into valuable biologically relevant δ-hydroxyl-α-amino acids. With a combination of experimental and theoretical methods, the mechanism for this 1,4-oxyimination reaction has been investigated. Theoretical calculations reveal that a radical chain mechanism might operate in the reaction.

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.

Photoredox Hydroxy-arylation of the Terminal Double Bond of N-Substituted 3-Methyleneisoindolin-1-ones in Visible Light

Mild and efficient ruthenium-catalyzed hydroxy-arylation of the terminal double bond of N-substituted 3-methyleneisoindolin-1-ones is described. The reaction takes place with aryl diazonium salt as the arylating reagent and water as the hydroxyl source in visible light at ambient temperature. The strategy entails vicinal difunctionalization of alkene and enables construction of 3-benzyl-3-hydroxyisoindolin-1-one heterocyclic scaffolds in moderate to good yields. C-C and C-O bonds are formed in one pot without any external additive and oxidant through an in situ generation of a carbocation intermediate in green light.

Photocatalytic difluoromethylarylation of unactivated alkenes via a (hetero)aryl neophyl-like radical migration

Photoredox-catalyzed addition of the difluoromethylradical to unactivated alkenes has been found to trigger neophyl-like aryl and heteroaryl migrations which allowed the construction of a diverse series of difluoromethyl ketones. The reaction featured mild reaction conditions and broad substrate scope.

Modular Difunctionalization of Unactivated Alkenes through Bio-Inspired Radical Ligand Transfer Catalysis

Development of visible light-mediated atom transfer radical addition of haloalkanes onto unsaturated hydrocarbons has seen rapid growth in recent years. However, due to its radical chain propagation mechanism, diverse functionality other than the pre-existing (pseudo-)halide on the alkyl halide source cannot be incorporated into target molecules in a one-step, economic fashion. Inspired by the prominent reactivities shown by cytochrome P450 hydroxylase and non-heme iron-dependent oxygenases, we herein report the first modular, dual catalytic difunctionalization of unactivated alkenes via manganese-catalyzed radical ligand transfer (RLT). This RLT elementary step involves a coordinated nucleophile rebounding to a carbon-centered radical to form a new C-X bond in analogy to the radical rebound step in metalloenzymes. The protocol leverages the synergetic cooperation of both a photocatalyst and earth-abundant manganese complex to deliver two radical species in succession to minimally functionalized alkenes, enabling modular diversification of the radical intermediate by a high-valent manganese species capable of delivering various external nucleophiles. A broad scope (97 examples, including drugs/natural product motifs), mild conditions, and excellent chemoselectivity were shown for a variety of substrates and fluoroalkyl fragments. Mechanistic and kinetics studies provide insights into the radical nature of the dual catalytic transformation and support radical ligand transfer (RLT) as a new strategy to deliver diverse functionality selectively to carbon-centered radicals.

Discovery of Natural Rosin Derivatives Containing Oxime Ester Moieties as Potential Antifungal Agents to Control Tomato Gray Mold Caused by Botrytis cinerea

Inspired by the application of natural products against pathogenic fungi, two series of dehydroabietyl oxime ester derivatives were synthesized using rosin as a raw material. Based on the evaluation and screening of in vitro antifungal activities against Botrytis cinerea (B. cinerea), Sclerotinia sclerotiorum, Valsa mali, Rhizoctonia solani, Fusarium oxysporum, and Alternaria alternata, compound 4f exhibited the best antifungal activity against B. cinerea, and its EC₅₀ was 0.798 mg/L, which was lower than that of the positive control trifloxystrobin (1.112 mg/L). The in vivo antifungal activity results showed that 4f had satisfactory protective and curative effects on tomato. Physiological and biochemical studies showed that the action mechanism of compound 4f against B. cinerea is to change the morphology and the ultrastructure of the mycelium, increase the permeability of the cell membrane, and cause nucleus and mitochondrial dysfunction, thus leading to apoptosis. In addition, qualitative and quantitative structure-activity relationship studies showed that the inductive and conjugative interactions between compound 4f and the target receptor form an electron transfer process, thereby achieving an antifungal effect. These results indicated that compound 4f, which was derived from the natural product rosin, is a novel potential fungicidal candidate against B. cinerea.

Radical-Mediated Functionalization of Internal Alkenes: Synthesis of Multisubstituted Allylic and Homoallylic Azides

Radical-mediated functionalization of alkenes provides a powerful tool for transformation of simple alkenes into numerous value-added products. The precedent radical functionalization of alkenes is mainly restricted to terminal alkenes, while the conversion of internal alkenes generally remains challenging, as the increased steric congestion on alkenes significantly conflicts with the intermolecular addition of radicals. Herein, we describe an efficient photoredox catalytic functionalization of internal trisubstituted alkenes, leading to a plethora of valuable multifunctionalized allylic and homoallylic azides, which are otherwise difficult to obtain. The azide products serve as versatile feedstock for construction of useful heterocycles. Allylic or homoallylic azides are selectively generated in the transformation, regulated by the regioselective deprotonation process. This method also features mild reaction conditions and high product diversity.

Visible-Light-Induced Alkylarylation of Unactivated Alkenes via Radical Addition/Truce-Smiles Rearrangement Cascade

We disclosed a visible-light-induced alkylarylation reaction of unactivated alkenes via a metal-free radical addition/aryl translocation cascade sequence. Distal olefinic sulfonate was designed as a unique molecular scaffold allowing for a domino process to synthesize valuable alkylarylated alcohols in good yields with excellent diastereoselectivity, featuring mild reaction conditions, broad substrate scope, and excellent functional group tolerance. The mechanism investigation suggests that a visible-light-induced radical chain process dominates the cascade transformation.

Organic photoredox catalytic amino-heteroarylation of unactivated olefins to access distal amino ketones

Here we describe a metal-free amino-heteroarylation of unactivated olefins via organic photoredox catalysis, providing a concise and efficient approach for the rapid synthesis of various δ (β, ε)-amino ketones under mild conditions. This protocol demonstrates that the new photocatalyst Cz-NI developed by our group has an excellent photoredox catalytic performance. Finally, a series of mechanistic experiments and DFT calculations indicate that this transformation undergoes a photoredox catalytic sequential radical addition/functional group migration process.

2-Pyridinylmethyl borrowing: base-promoted C-alkylation of (pyridin-2-yl)-methyl alcohols with ketones via cleavage of unstrained C(sp3)–C(sp3) bonds

2-Pyridinylmethyl Borrowing: Transition-metal-free 2-pyridinylmethyl borrowing C-alkylation of alcohols access to ketones is developed. This unstrained C(sp3)–C(sp3) bonds cleavage of unactivated alcohols avoids the use of transition metals.

1,2-Difunctionalizations of alkynes entailing concomitant C–C and C–N bond-forming carboamination reactions

Vicinal carboamination of alkynes is a highly reliable and efficient practical strategy for the quick preparation of valuable and diverse amine derivatives starting from simple synthons. The last decade has witnessed numerous practical methods employing transition-metal-based/metal-free carboamination approaches using alkynes for the synthesis of these N-bearing entities. Driven by the renaissance of transition metal catalysis, intermolecular and intramolecular carboamination of alkynes comprising concomitant C–N and C–C bond formation has been studied extensively. In contrast to metal catalysis, though analogous metal-free approaches have been relatively less explored in the literature, they serve as alternatives to these expensive approaches. Despite this significant progress, reviews documenting such examples are sporadic; as a result, most reports of this type remained scattered throughout the literature, thereby hampering further developments in this escalating field. In this review, different conceptual approaches will be discussed and examples from the literature will be presented. Further, the reader will get insight into the mechanisms of different transformations.

The 1,2-difunctionalization of alkynes happening through concomitant C–C and C–N bond formation strategies have provide an unified access to diversely functionalized N-bearing heterocycles.

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.

Intermolecular 1,2-Difunctionalization of Alkenes Enabled by Fluoroamide-Directed Remote Benzyl C(sp3)-H Functionalization

A copper-catalyzed remote benzylic C-H functionalization strategy enabling 1,2-difunctionalization of alkenes with 2-methylbenzeneamides and nucleophiles, including alcohols, indoles, pyrroles, and the intrinsic amino groups, is reported, which is characterized by its redox-neutral conditions, exquisite site-selectivity, broad substrate scope, and wide utilizations of late-stage modifying bioactive molecules. This reaction proceeds through nitrogen-centered radical generation, hydrogen atom transfer, benzylic radical addition across the alkenes, single-electron oxidation, and carbocation electrophilic course cascades. While using external nucleophiles manipulates three-component alkene alkylalkoxylation and alkyl-heteroarylation with 2-methylbenzeneamides to access dialkyl ethers, 3-alkylindoles, and 3-alkylpyrroles, omitting the external nucleophiles results in two-component alkylamidation ([5+2] annulation) of alkenes with 2-methylbenzeneamides to benzo-[f][1,2]thiazepine 1,1-dioxides.

Three-component 1,2-dicarbofunctionalization of alkenes involving alkyl radicals

1,2-Dicarbofunctionalization of alkenes represents an appealing strategy for chemical bond formation in organic synthesis, which could enable the rapid construction of molecular complexity from simple and readily available starting materials by incorporating two functional groups onto a carbon-carbon double bond in one step. In this field, the dicarbofunctionalization of alkenes with different alkyl radicals in a controlled manner represents an elegant and versatile strategy to access structurally diverse functionalized alkanes, which have witnessed significant progress over the last five years. Due to the importance of alkyl radicals in organic synthesis and medicinal chemistry, this review provides a comprehensive perspective on the development of alkyl radical precursors including electrophilic precursors such as alkyl halides, alkyl peroxides, alkyl NHP esters, cycloketone oxime esters, and Katritzky pyridinium salts, and nucleophilic precursors such as alkyl acids, alkyl oxalates, alkylborates, alkylsilicates, and unactivated hydrocarbons, which generate alkyl radicals by photocatalysis or transition metal catalysis to engage in dicarbofunctionalization under oxidative reaction conditions, redox-neutral conditions, or reductive conditions. The mechanisms of these dicarbofunctionalization reactions have also been discussed in detail.

Electrifying Phthalimide-N-Oxyl (PINO) Radical Chemistry: Anodically Induced Dioxygenation of Vinyl Arenes with N-Hydroxyphthalimide

An electrochemical process of free-radical difunctionalization of vinyl arenes with N-hydroxyphthalimide resulting in vicinal dioxyphthalimides was discovered. The reaction proceeds with the use of pyridinium perchlorate and pyridine as a supporting electrolyte and a base, respectively. The present approach involves the anodic generation of stabilized phthalimide-N-oxyl (PINO) radical, which adds to the carbon-carbon double bond of vinyl arenes and recombines with the subsequently formed benzylic radical. A wide range of dioxyphthalimides were obtained in yields up to 81%.

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 1,4/5-Amino Shift Enables Access to Fluoroalkyl-Containing Primary β(γ)-Aminoketones under Metal-Free Conditions

A novel radical 1,4/5-amino shift from the oxygen center of alkene-tethered diphenyl ketoxime ethers to the carbon center to achieve high value-added fluoroalkyl-containing primary β(γ)-amino-ketones is reported. Mechanism studies reveal that the migration is triggered by the alkene addition of fluoroalkyl radical derived from the electron donor-acceptor (EDA) complex of Togni's reagent II or fluoroalkyl iodides and quinuclidine, and involves a unique 5(6)-exo-trig cyclization of the carbon-centered radical onto the N-atom of ketoxime ethers followed by a cascade sequence of N-O bond cleavage and dehydrogenation. Notably, besides Togni's reagent II and fluoroalkyl iodides, this protocol is also compatible with other radical precursors to provide various functionalized primary aminoketones.

Cobalt-Catalyzed Highly Regioselective Three-Component Arylcarboxylation of Acrylate with Aryl Bromides and Carbon Dioxide

Cobalt-catalyzed regioselective three-component arylcarboxylation of acrylate with aryl bromides and carbon dioxide has been developed. The reaction is carried out by using cobalt chloride as a precatalyst and zinc powder as a reducing reagent under CO₂ (1 atm) at 40 °C. A range of aryl bromides are used for this reaction, leading to a series of valuable carboxylic acids with high regioselectivity and functional-group compatibility. Mechanistic experiments and DFT calculations indicate that this arylcarboxylation reaction involves the reaction of CO₂ with a cobalt enolate intermediate to form the C-C bond.

Generation of Heteroaryl-Substituted Sulfonyl Compounds from Sulfur Dioxide via Remote Heteroaryl ipso-Migration

The generation of heteroaryl-substituted sulfonyl compounds via a catalyst-, base-, and additive-free three-component reaction of heteroaryl-substituted tertiary alcohols, aryldiazonium tetrafluoroborates, and DABCO·(SO₂)₂ under mild conditions is developed. Various functional groups are tolerated well in this transformation, and a broad substrate scope is demonstrated. A preliminary mechanistic investigation shows that this reaction undergoes a radical process, including the insertion of sulfur dioxide, sulfonyl radical addition to unactivated alkene, and remote heteroaryl ipso-migration.

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.

Alkene Difunctionalization Triggered by a Stabilized Allenyl Radical: Concomitant Installation of Two Unsaturated C-C Bonds

Radical-mediated difunctionalization of alkenes provides a promising approach to introduce one alkenyl or alkynyl group to target compounds. However, simultaneous installation of two unsaturated C-C bonds via alkene difunctionalization remains elusive, attributable to the high instability and transient lifetimes of alkenyl and alkynyl radicals. Herein, we report the photocatalytic 1,2-alkynylalkenylation and 1,2-enynylalkenylation of alkenes for the first time, triggered by the intermolecular addition of a stabilized allenyl radical to an alkene. A portfolio of strategically designed, easily accessible dual-function reagents are applied to a radical docking-migration cascade. The protocol has broad substrate scope and efficiently increases the degree of unsaturation.

Copper-Catalyzed Aminoheteroarylation of Unactivated Alkenes through Distal Heteroaryl Migration

We report a copper-catalyzed aminoheteroarylation of unactivated alkenes to access valuable heteroarylethylamine motif. The developed reaction features a copper-catalyzed intermolecular electrophilic amination of the alkenes followed by a migratory heteroarylation. The method applies on alcohol-, amide-, and ether-containing alkenes, overcoming the common requirement of a hydroxyl motif in previous migratory difunctionalization reactions. This reaction is effective for the introduction of diverse aliphatic amines and has good functional group tolerance, which is particularly useful for richly functionalized heteroarenes. This migration-involved reaction was found well suited as a powerful ring expansion approach for the construction of medium-sized rings that are in great demand in medicinal chemistry.

Oxidative alkylation/alkynylation of terminal alkenes via alkylaldehyde decarbonylation and 1,2-alkynyl migration

A metal-free oxidative alkene alkylation/alkynylation of 1,4-enyn-3-ols with alkylaldehydes has been achieved, which offers a general access to the challenging quaternary carbon-containing but-3-yn-1-ones. The method features excellent functional group tolerance, broad substrate scope and exquisite selectivity, and provides a strategy for the difunctionalization of functional alkenes and utilization of alkylaldehydes as alkylating reagents through decarbonylation and 1,2-alkynyl migration.

Cyanoalkylation/alkynylation of allylic alcohol through intramolecular radical 1,2-alkynyl migration

A di-tert-butyl peroxide (DTBP)-promoted difunctionalization of α-aryl α-alkynyl allylic alcohols with alkyl nitriles was developed, affording a series of α-alkynyl γ-cyano functionalized ketones in moderate yields. This procedure involved C(sp³)-H bond cleavage of alkyl nitriles and radical 3-exo-dig cyclization. After this, radical 1,2-alkynyl migration is preferred rather than 1,2-aryl migration.

Copper-Catalyzed Radical 1,2-Carbotrifluoromethylselenolation of Alkenes under Ambient Conditions

We have described a copper-catalyzed radical 1,2-carbotrifluoromethylselenolation of alkenes using the readily available alkyl halides and (Me₄N)SeCF₃ salt. Critical to the success is the use of a proline-based N,N,P-ligand to enhance the reducing capability of copper for easy conversion of diverse alkyl halides to the corresponding radicals via a single-electron transfer process. The reaction features a broad substrate scope, including various mono-, di-, and trisubstituted alkenes with many functional groups.

Metal-free visible-light-induced photoredox-catalyzed intermolecular pyridylation/phosphinoylation of alkenes

A visible-light-induced and photoredox-catalyzed intermolecular pyridylation/phosphinoylation of alkenes using 4-cyanopyridine and diphenylphosphine oxide under mild metal-free conditions has been reported.