Cu-Catalyzed Enantioselective Alkylarylation of Vinylarenes Enabled by Chiral Binaphthyl-BOX Hybrid Ligands

Direct stereoselective C(sp3)-H alkylation of saturated heterocycles using olefins

Despite cross-coupling strategies that enable the functionalization of aromatic heterocycles, the enantioselective C(sp3)-H alkylation of readily available saturated hydrocarbons to construct C(sp3)-C(sp3) bonds remains a formidable challenge. Here we describe a nickel-catalysed enantioselective C(sp3)-H alkylation of saturated heterocycles using olefins, providing an efficient strategy for the stereoselective construction of C(sp3)-C(sp3) bonds. Using readily available and stable olefins and simple saturated nitrogen and oxygen heterocycles as prochiral nucleophiles, the coupling reactions proceed under mild conditions and exhibit broad scope and high functional group tolerance. Furthermore, the enantio- and diastereoselective C(sp3)-H alkylation of saturated hydrocarbons with alkenyl boronates has been achieved, enabling the synthesis of versatile alkyl boronates containing 1,2-adjacent C(sp3) stereocentres. Application of this approach to the late-stage modification of natural products and drugs, as well as to the enantioselective synthesis of a range of chiral building blocks and natural products, is demonstrated.

Selective Ni(I)/Ni(III) Process for Consecutive Geminal C(sp3)-C(sp2) Bond Formation

Ni-catalyzed multicomponent cross-couplings have emerged as a powerful strategy for efficiently constructing complex molecular architectures from a diverse array of organic halides. Despite its potential, selectively forming multiple chemical bonds in a single operation, particularly in the realm of cross-electrophile coupling catalysis, remains a significant challenge. In this study, we have developed a consecutive open-shell reductive Ni catalysis, enabling the formation of two geminal C(sp3)-C(sp2) bonds from two stereoelectronically similar C(sp2)-I reactants in conjunction with a methylene electrophile. Using zirconaaziridine and elemental Mg0 as reductants, this protocol exhibits broad applicability across a wide range of (hetero)aromatic, alkenyl, and glycal halides, allowing for the rapid assembly of medicinally relevant scaffolds with excellent functional group tolerance. Further kinetic studies suggest a dual "sequential reduction" catalytic process facilitated by a zirconaaziridine-mediated redox-transmetalation process in Ni catalysis. Notably, the concerted oxidative addition of Ni(I)-I across a C(sp2)-I bond, as well as the halide atom abstraction among various C(sp3) electrophiles by an open-shell C(sp2)-Ni(I) species, can proceed with high selectivity. The use of an unsymmetrical methylene electrophile with exceptionally high reactivity in XEC resulted in the rapid accumulation of a benzylic or allylic electrophile intermediate at the outset of reaction, thereby finely controlling the coupling sequence.

Cu-Catalyzed Asymmetric Three-Component Radical Acylarylation of Vinylarenes with Aldehydes and Aryl Boronic Acids

The direct use of readily available aldehydes as acyl radical precursors has facilitated diverse three-component acylative difunctionalization reactions of alkenes, offering a powerful route to synthesize β-branched ketones. However, asymmetric three-component acylative difunctionalization of alkenes with aldehydes still remains elusive. Here we report a copper-catalyzed asymmetric three-component radical acylarylation of vinylarenes with aldehydes and aryl boronic acids. This method begins with acyl radical formation from an aldehyde via hydrogen atom transfer. The acyl radical adds to the alkene, forming a new benzylic radical that then undergoes copper-catalyzed enantioselective arylation. A chiral binaphthyl-tethered bisoxazoline ligand is essential for achieving high stereocontrol. This strategy enables the direct synthesis of a range of synthetically valuable chiral β,β-diaryl ketones from aldehydes and vinylarenes.

Photocatalysis Meets Copper Catalysis: A New Opportunity for Asymmetric Multicomponent Radical Cross-Coupling Reactions

ConspectusIn recent years, radical-mediated cross-coupling reactions have emerged as a compelling strategy for achieving a rich diversity in molecular topologies under benign conditions. However, the inherent high reactivity of radicals presents considerable challenges in controlling reaction pathways and selectivity, which often results in a limited range of substrates and a constrained reaction profile. Given the capacity of visible-light photoredox catalysis to generate a wide variety of reactive radicals and radical ions in a controlled manner and the propensity of copper complexes toward radical species, we envisaged that the synergy between chiral copper catalysts and photoactive catalysts would pave the way for developing innovative strategies. This integration is poised to unlock a broad spectrum of enantioselective multicomponent radical cross-coupling reactions.In this Account, we describe our insights and recent efforts in the realm of enantioselective multicomponent radical cross-coupling reactions. These advancements have been achieved through the innovative application of dual photoredox/copper catalysis or bifunctional copper catalysis under visible light irradiation. Our work is systematically divided into two sections based on the activation modes. The first section focuses on photoinduced copper-catalyzed chiral C-C and C-O bond formation through a radical addition/nucleophilic trap sequence. Our discussion of chiral C-C bond formation is particularly concentrated on the asymmetric carbocyanation and carboarylation of vinylarenes, 1,3-enynes, and 1,3-dienes. Our findings underscore that irradiation with visible light can adeptly modulate the pace of radical generation, thus orchestrating consecutive reaction stages and ensuring the attainment of both chemo- and stereoselectivity. In the domain of chiral C-O bond formation, leveraging carboxylic acids as a nucleophilic oxygen source, we introduce a suite of esterification reactions of benzylic, allylic, and propargylic radicals. These radicals are derived from a variety of radical precursors, showcasing the versatility of our approach. The following section highlights our innovative discovery in the field of dual photoredox/copper catalysis, which enables enantioselective three-component radical transformations via the direct activation of aromatic alkenes. This methodology begins with the generation of formal distonic radical anions through the photocatalytic single-electron reduction of aromatic alkenes, thus, enabling orthogonal reactivity. Employing H2O, D2O, and CO2 as external electrophile agents, we have developed three types of radical cyanofunctionalization reactions: hydrocyanation, deuteriocyanation, and cyanocarboxylation. These reactions provide practical access to diversely functionalized chiral nitriles with high enantiomeric excess.Collectively, these synthetic methodologies highlight the immense potential inherent in the synergistic integration of photocatalysis and asymmetric copper catalysis. This Account aspires to deepen our comprehension of the advantages conferred by these catalytic systems, elucidating the crucial role of photocatalysis in facilitating enantioselective multicomponent radical cross-couplings. We anticipate that this Account will provide valuable insights and stimulate the evolution of innovative methodologies within this rapidly expanding field.

A General Copper-Box System for the Asymmetric Arylative Functionalization of Benzylic, Propargylic or Allenylic Radicals

Radical-involved arylative cross-coupling reactions have recently emerged as an attractive strategy to access valuable aryl-substituted motifs. However, there still exist several challenges such as limited scope of radical precursors/acceptors, and lack of general asymmetric catalytic systems, especially regarding the multicomponent variants. Herein, we reported a general copper-Box system for asymmetric three-component arylative radical cross-coupling of vinylarenes and 1,3-enynes, with oxime carbonates and aryl boronic acids. The reactions proceed under practical conditions in the absence or presence of visible-light irradiation, affording chiral 1,1-diarylalkanes, benzylic alkynes and allenes with good enantioselectivities. Mechanistic studies imply that the copper/Box complexes play a dual role in both radical generation and ensuing asymmetric cross-coupling. In the cases of 1,3-enynes, visible-light irradiation could improve the activity of copper/Box complex toward the initial radical generation, enabling better efficiency match between radical formation and cross-coupling.

Nickel/Photoredox-Catalyzed Asymmetric Three-Component Cross-Coupling To Access Enantioenriched 1,1-Diaryl(heteroaryl)alkanes

An enantioselective 1,2-dicarbofunctionalization of vinyl (hetero)arenes with alkyl bromides and aryl bromides through nickel/photoredox catalysis is described. This three-component enantioselective domino alkyl arylation of vinyl (hetero)arenes could generate a diverse array of enantioenriched 1,1-diaryl(heteroaryl)alkanes with good to excellent yields (up to 88%) and high enantioselectivities (up to 99% ee). This transformation could proceed well under mild conditions with excellent chemo- and regioselectivity due to the avoidance of the use of air- and moisture-sensitive organometallic reagents and stoichiometric metal reductants. Mechanistic studies suggested that the alkyl radical is generated via NiI species or photocatalyst.

Photoinduced copper-catalyzed asymmetric cyanoalkylalkynylation of alkenes, terminal alkynes, and oximes

The asymmetric dicarbofunctionalization of alkenes via a radical relay process can provide routes to diverse hydrocarbon derivatives. Three-component carboalkynylation, limited to particular alkyl halides and using readily available cycloketone oxime esters as redox-active precursors, is restricted by the available pool of suitable chiral ligands for broadening the redox potential window of copper complexes and simultaneously creating the enantiocontrol environment. Herein, we report a new hybrid tridentate ligand bearing a guanidine-amide-pyridine unit for photoinduced copper-catalyzed cyanoalkylalkynylation of alkenes. Leveraging the copper catalyst's redox capability is achieved via merging the electron-rich ligand with a readily organized configuration and enhanced absorption in the visible light range, which also facilitates the enantioselectivity. The generality of the catalyst system is exemplified by the efficacy across a number of alkenes, terminal alkynes and cycloketone oxime esters, working smoothly to give alkyne-bearing nitriles with good yields and excellent enantioselectivity. A mechanistic study reveals that the chiral copper catalyst meets the requirements of possessing sufficient reduction ability, good light absorption properties, and appropriate steric hindrance.

One-pot sequential synthesis of unsymmetrical diarylmethanes using methylene chloride as a C1-synthon

Bisindolylmethane (BIM) and its derivatives are widely used in the pharmaceutical industry due to their significant biological activities. However, most reported synthetic methods are focused on the synthesis of symmetric BIMs, while the synthesis of unsymmetrical BIMs remains a challenge. Herein, an unprecedented two-step one-pot method to afford unsymmetrically substituted 3,3'-BIM frameworks, using methylene chloride (DCM) as the C1-synthon is reported. In this protocol, the formation of two C-C bonds can be achieved via a one-pot reaction. The utility of commercially available phenols and anilines was also demonstrated in the construction of unsymmetrical diarylmethanes. This protocol provides a straightforward approach to access diverse unsymmetrical diarylmethane derivatives under simple and mild conditions. The broad substrate compatibility and good functional group tolerance of the protocol support its practical application potential.

Development of Axially Chiral Pyridylidene Amine Ligands and their Application in Pd-Catalyzed Enantioselective Allylic Substitution

A series of novel axially chiral pyridylidene amine (PYE) ligands has been developed, and their catalytic capability has been demonstrated in various highly efficient and enantioselective Pd-catalyzed asymmetric allylic substitutions. A density-functional theory (DFT) study explains the preferential enantiocontrol in the key transition states of the axially chiral PYE ligand-promoted Pd-catalyzed allylic alkylation.

Copper-Catalyzed sp2 C-H Arylation and Alkynylation of Allenes via Hydrogen Atom Abstraction

Development of methods for the sp2 C-H transformations of allenes has received much attention, and it presents a powerful tool for the synthesis of complicated allene-containing bioactive molecules. With a copper-catalyzed radical relay, sp2 allenic C-H arylation and alkynylation were established herein, using various aryl boronic acids and trimethoxysilyl-substituted alkynes as carbon nucleophiles and using electrophilic N-F reagents as nitrogen-centered radical precursors. These methods featured excellent site selectivity to deliver fully substituted allenes efficiently. Moreover, with silyl-substituted allenes as substrates, a subsequent dual sp2 C-H functionalization process was established as well, which allowed for the divergent synthesis of multifunctionalized allenes, significantly expanding their chemical spaces.

Fe-Catalyzed Fluoroalkyl(hetero)arylation of Vinyl Azaarenes: Rapid and Modular Synthesis of Unsymmetrical 1,1-Bis(hetero)arylalkanes

In contrast to transition-metal-catalyzed difunctionalization of activated alkenes, selective alkylarylation of vinyl azaarenes is underdeveloped. Consequently, the lack of modular and rapid syntheses of 1,1-bis(hetero)arylalkanes limits their exploration in medicinal chemistry. Herein we report a protocol using commercially available iron salts, bisphosphine ligands, fluoroalkyl halides, and Grignard reagents that enables the selective 1,2-fluoroalkyl(hetero)arylation of vinyl azaarenes. We demonstrate the versatility and robustness of the method through the selective synthesis of a range of unsymmetrical 1,1-bis(hetero)arylalkenes, including pyridine N-oxides, triazoles, pyrazines, carbazoles, indazoles, and 1,2-azaborines. Mechanistic insights from experimental and computational investigations support a radical pathway and provide insights into the role of non-covalent interactions in iron catalysis.

Aromatization-driven deconstructive functionalization of spiro dihydroquinazolinones via dual photoredox/nickel catalysis

Aromatization-driven deconstruction and functionalization of spiro dihydroquinazolinones via dual photoredox/nickel catalysis is developed. The aromatization effect was introduced to synergistically drive unstrained cyclic C-C bond cleavage, with the aim of overcoming the ring-size limitation of nitrogen-centered radical induced deconstruction of carbocycles. Herein, we demonstrate the synergistic photoredox/nickel catalyzed deconstructive cross-coupling of spiro dihydroquinazolinones with organic halides. Remarkably, structurally diverse organic halides including aryl, alkenyl, alkynyl, and alkyl bromides were compatible for the coupling. In addition, this protocol is also characterized by its mild and redox-neutral conditions, excellent functional group compatibility, high atom economy, and easy scalability. A telescoped procedure involving condensation and ring-opening/coupling was found to be accessible. This work provides a complementary strategy to the existing radical-mediated C-C bond cleavage of unstrained carbocycles.

Photoredox-catalyzed alkylarylation of activated alkenes via a ring-opening/Truce-Smiles rearrangement cascade

A photoredox-catalyzed alkylarylation of activated alkenes via a radical C-C bond cleavage/Truce-Smiles rearrangement cascade is developed. The protocol features mild and redox-neutral conditions, broad substrate scope and excellent functional group compatibility, providing a facile and efficient approach to the long-chain distal keto-amides with all-carbon quaternary centers at the alpha position.

Photoredox-Catalyzed Decarboxylative Cross-Coupling Reaction to Synthesis Unsymmetrical Diarylmethanes

The photoredox-catalyzed decarboxylative cross-coupling reaction of aryl acetic acids and aryl nitriles has been achieved under an argon atmosphere in high yields. This method provides a fast way to obtain prevalent aryl acetic acids from an abundant natural source. A tentative radical mechanism has been proposed.

Asymmetric, Remote C(sp3)-H Arylation via Sulfinyl-Smiles Rearrangement

An efficient asymmetric remote arylation of C(sp3)-H bonds under photoredox conditions is described here. The reaction features the addition radicals to a double bond followed by a site-selective radical translocation (1,n-hydrogen atom transfer) as well as a stereocontrolled aryl migration via sulfinyl-Smiles rearrangement furnishing a wide range of chiral α-arylated amides with up to >99 : 1 er. Mechanistic studies indicate that the sulfinamide group governs the stereochemistry of the product with the aryl migration being the rate determining step preceded by a kinetically favored 1,n-HAT process.

Copper-catalyzed oxidative cyclization of 2-(1H-pyrrol-1-yl)aniline and alkylsilyl peroxides: a route to pyrrolo[1,2-a]quinoxalines

An efficient method was developed for the one-pot construction of pyrrolo[1,2-a]quinoxalines via a Cu(II)-catalyzed domino reaction between 2-(1H-pyrrol-1-yl)anilines and alkylsilyl peroxides. This reaction proceeds through C-C bond cleavage and new C-C and C-N bond formation. A mechanistic study suggests that alkyl radical species participate in the cascade reaction.

Metal-catalyzed asymmetric reactions enabled by organic peroxides

As a class of multifunctional reagents, organic peroxides play vital roles in the chemical industry, pharmaceutical synthesis and polymerization reactions. Metal-catalyzed asymmetric catalysis has emerged as one of the most straightforward and efficient strategies to construct enantioenriched molecules, and an increasing number of metal-catalyzed asymmetric reactions enabled by organic peroxides have been disclosed by researchers in recent years. Despite remarkable progress, the types of asymmetric reactions facilitated by organic peroxides remain limited and the catalysis systems need to be further broadened. To the best of our knowledge, there is still no review devoted to summarizing the reactions from this perspective. In this review, we will endeavor to highlight the advances in metal-catalyzed asymmetric reactions enabled by organic peroxides. We hope that this survey will summarize the functions of organic peroxides in catalytic reactions, improve the understanding of these compounds and inspire future developments in this area.

Trifluoromethylarylation of alkenes using anilines

Nitrogen containing compounds, such as anilines, are some of the most widespread and useful chemical species, although their high and unselective reactivity has prevented their incorporation into many interesting transformations, such as the functionalization of alkenes. Herein we report a method that allows the trifluoromethylarylation of alkenes using anilines, for the first time, with no need for additives, transition metals, photocatalysts or an excess of reagents. An in-depth mechanistic study reveals the key role of hexafluoroisopropanol (HFIP) as a unique solvent, establishing a hydrogen bonding network with aniline and trifluoromethyl reagent, that is responsible for the altered reactivity and exquisite selectivity. This work uncovers a new mode of reactivity that involves the use of abundant anilines as a non-prefunctionalized aromatic source and the simultaneous activation of trifluoromethyl hypervalent iodine reagent.

NHC-catalyzed radical acylation of cycloalkyl silyl peroxides to access 1,6-,1,7-, and 1,8-diketones

An unprecedented N-heterocyclic carbene (NHC)-catalyzed radical acylation of cycloalkyl silyl peroxides was developed using readily available aldehydes as the acylating agents. This protocol provides an exceptionally useful method for the efficient and rapid synthesis of long-chain 1,6-/1,7-/1,8-diketones, especially unsymmetrical ones. This strategy also has the advantages of mild conditions, good functional group compatibility, and potential applications in the late-stage functionalization of aldehydes with bioactive fragments and in the construction of long-chain complex bioactive molecules.

Recent Advances in the Enantioselective Radical Reactions

The review covers research published since 2017 and is focused on enantioselective synthesis using radical reactions. It describes recent approaches to the asymmetric synthesis of chiral molecules based on the application of the metal catalysis, dual metal and organocatalysis and finally, pure organocatalysis including enzyme catalysis. This review focuses on the synthetic aspects of the methodology and tries to show which compounds can be obtained in enantiomerically enriched forms.

5-Fluoro-3-(1H-indol-3-ylmeth-yl)-1H-indole

The title compound, C17H13FN2, was synthesized as a potential ligand for the construction of metal-organic frameworks. The two indole motifs present two potential coordination modes. It crystallizes in the ortho-rhom-bic system with space group P212121. The dihedral angle between the fused ring systems is 68.77 (10)°. Weak F⋯H inter-actions are observed in the crystal.

Copper-Catalyzed Asymmetric Functionalization of Vinyl Radicals for the Access to Vinylarene Atropisomers

A novel asymmetric radical strategy for the straightforward synthesis of atropisomerically chiral vinyl arenes has been established herein, proceeding through copper-catalyzed atroposelective cyanation/azidation of aryl-substituted vinyl radicals. Critical to the success of the radical relay process is the atroposelective capture of the highly reactive vinyl radicals with chiral L*Cu(II) cyanide or azide species. Moreover, these axially chiral vinylarene products can be easily transformed into atropisomerically enriched amides and amines, enantiomerically enriched benzyl nitriles via an axis-to-center chirality transfer process, and an atropisomerically pure organocatalyst for the chemo-, diastereo-, and enantioselective (4 + 2) cyclization reaction.

Copper-Catalyzed Chemo- and Enantioselective Radical 1,2-Carbophosphonylation of Styrenes

The copper-catalyzed enantioselective radical difunctionalization of alkenes from readily available alkyl halides and organophosphorus reagents possessing a P-H bond provides an appealing approach for the synthesis of α-chiral alkyl phosphorus compounds. The major challenge arises from the easy generation of a P-centered radical from the P-H-type reagent and its facile addition to the terminal side of alkenes, leading to reverse chemoselectivity. We herein disclose a radical 1,2-carbophosphonylation of styrenes in a highly chemo- and enantioselective manner. The key to the success lies in not only the implementation of dialkyl phosphites with a strong bond dissociation energy to promote the desired chemoselectivity but also the utilization of an anionic chiral N,N,N-ligand to forge the chiral C(sp³ )-P bond. The developed Cu/N,N,N-ligand catalyst has enriched our library of single-electron transfer catalysts in the enantioselective radical transformations.

When all C-C breaks LO-Ose

Organic peroxides are becoming popular intermediates for novel chemical transformations. The weak O-O bond is readily reduced by transition metals, including iron and copper, to initiate a radical cascade process that breaks C-C bonds. Great potential exists for the rapid generation of complexity, originating from the ability to couple the resulting free radicals with a wide range of partners. First, this review article discusses the history and synthesis of organic peroxides, providing the context necessary to understand this methodology. Then, it highlights 91 examples of recent applications of the radical functionalization of C-C bonds accessed through the transition metal-mediated reduction of organic peroxides. Finally, we provide some comments about safety when working with organic peroxides.

Nickel-Catalyzed Radical Ring-Opening Phosphorylation of Cycloalkyl Hydroperoxides Leading to Distal Acylphosphine Oxides

A facile and efficient nickel-catalyzed C-C bond cleavage/phosphorylation of various cycloalkyl hydroperoxides was developed. This radical ring-opening strategy provided practical access to structurally diverse distal ketophosphine oxides in one pot through concurrent C═O/C-P bond formation with high atom economy under mild room temperature and base-free conditions.

Asymmetric Ketoalkylation/Rearrangement of Alkyenlfurans via Synergistic Photoredox/Brønsted Acid Catalysis

An enantioselective three-component rearrangement of alkenylfurans with various cycloalkyl silyl peroxides and anilines has been developed by merging photoredox catalysis with chiral Brønsted acid catalysis. This protocol provides expedient access to a broad spectrum of ketoalkyl-functionalized 4-aminocyclopentenones in high yields with excellent enantio- and diastereoselectivities. Diverse functional groups can be introduced via facile product derivations.

Switchable Radical Carbonylation by Philicity Regulation

Carbonylation reactions involving CO as readily available C1 synthons have become one of the most important tools for the construction of carbonyl compounds from feedstock chemicals. Despite numerous catalytic methods for carbonylation reactions proceeding via ionic or radical pathways, an inherent limitation to these methods is the need to control switchable single and double carbonylative formation of value-added products from the same and simple starting materials. Here, we describe a new strategy that exploits photoredox catalysis to regulate the philicity of amine coupling partners to drive switchable radical carbonylation reactions. In double carbonylation, amines were first transformed into nitrogen radical cations by single-electron transfer-oxidation and coupled with CO to form carbamoyl radicals, which further underwent radical cross-coupling with the incipient cyanoalkyl acyl radicals to afford the double carbonylation products. Upon the addition of stoichiometric 4-dimethylaminopyridine (DMAP), DMAP competitively traps the initially formed cyanoalkyl acyl radical to form the relatively stabilized cyanoalkyl acyl-DMAP salts that engaged in the subsequent substitution with the nucleophilic amines to produce the single carbonylation products. The reaction proceeded smoothly with excellent selectivity in the presence of various amine nucleophiles at room temperature, generating valuable amides and α-ketoamides in a versatile and controlled fashion. Combined experimental and computational studies provided mechanistic insights into the possible pathways.

Catalytic Asymmetric Diarylation of Internal Acyclic Styrenes and Enamides

Enantioselective transformations of olefins are among the most important strategies for the asymmetric synthesis of organic compounds. Chemo-, diastereo-, and stereoselective control of reactions with internal acyclic alkenes for the construction of functionalized acyclic alkanes still remain a persistent challenge. Here, we report a palladium-catalyzed asymmetric regiodivergent Heck-type diarylation of internal acyclic alkenes. The 1,2-diarylation of two accessible acyclic alkenes, cinnamyl carbamates and enamides with diazonium salts and aromatic boronic acids, furnishes products containing vicinal stereogenic centers via the stereospecific formation of carbonyl coordination-assisted transient palladacycles. Moreover, the asymmetric migratory diarylation of enamides enables the formation of incontiguous stereocenters by an interrupted diastereoselective 1,3-chain-walking process. This protocol streamlines access to highly functionalized multisubstituted enantioenriched carbamates and amine derivatives which are embedded in the key biologically active motifs.

Fe-Catalyzed Dicarbofunctionalization of Vinylarenes with Alkylsilyl Peroxides and β-Keto Carbonyl Substrates

The formation of two carbon-carbon bonds using vinylarenes with alkylsilyl peroxides and β-keto carbonyl substrates is effected by the presence of catalytic Fe(OTf)₂ under mild reaction conditions. A variety of vinylarenes with different substituents can be utilized in combination with several different alkylsilyl peroxides and β-keto carbonyl substrates.

Copper-catalyzed radical relay in C(sp3)-H functionalization

Radical-involved transition metal (TM) catalysis has greatly enabled new reactivities in recent decades. Copper-catalyzed radical relay offers enormous potential in C(sp³)-H functionalization which combines the unique regioselectivity of hydrogen atom transfer (HAT) and the versatility of copper-catalyzed cross-coupling. More importantly, significant progress has been achieved in asymmetric C-H functionalization through judicious ligand design. This tutorial review will highlight the recent advances in this rapidly growing area, and we hope this survey will inspire future strategic developments for selective C(sp³)-H functionalization.

Metal-free, visible-light induced enantioselective three-component dicarbofunctionalization and oxytrifluoromethylation of enamines via chiral phosphoric acid catalysis

Using diverse carbon-centered radical precursors and electron-rich (hetero)aromatics and alcohols as nucleophiles, a visible-light driven chiral phosphoric acid (CPA) catalyzed asymmetric intermolecular, three-component radical-initiated dicarbofunctionalization and oxytrifluoromethylation of enamines was developed, which provides a straightforward access to chiral arylmethylamines, aza-hemiacetals and γ-amino acid derivatives with excellent enantioselectivity. As far as we know, this is the first example of constructing a chiral C–O bond using simple alcohols via visible-light photocatalysis. Chiral phosphoric acid played multiple roles in the reaction, including controlling the reaction stereoselectivity and promoting the generation of radical intermediates by activating Togni's reagent. Mechanistic studies also suggested the importance of the N–H bond of the enamine and indole for the reactions.

We have developed a metal-free, visible-light driven chiral phosphoric acid catalyzed asymmetric intermolecular, three-component radical-initiated dicarbofunctionalization and oxytrifluoromethylation of enamines.

Nickel-Catalyzed Allylic Defluorinative Cross-Electrophile Coupling with Cycloalkyl Silyl Peroxides as the Alkyl Source

Herein we demonstrate the first successful application of cycloalkyl silyl peroxides (CSP) as an electrophilic coupling partner in the cross-electrophile coupling reaction. Diverse CSP are efficiently cross-coupled with an array of α-trifluoromethyl alkenes under the catalysis of nickel with the assistance of zinc as the reducing agent. This method allows the use of unstrained CSP as the carbonyl-containing alkyl source in the allylic defluorinative reaction, to access a variety of gem-difluoroalkenes bearing a pendent ketone moiety with high functionality tolerance.

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.

Ni-Catalyzed Arylbenzylation of Alkenylarenes: Kinetic Studies Reveal Autocatalysis by ZnX2 *

We report a Ni-catalyzed regioselective arylbenzylation of alkenylarenes with benzyl halides and arylzinc reagents. The reaction furnishes differently substituted 1,1,3-triarylpropyl structures that are reminiscent of the cores of oligoresveratrol natural products. The reaction is also compatible for the coupling of internal alkenes, secondary benzyl halides and variously substituted arylzinc reagents. Kinetic studies reveal that the reaction proceeds with a rate-limiting single-electron-transfer process and is autocatalyzed by in-situ-generated ZnX2 . The reaction rate is amplified by a factor of three through autocatalysis upon addition of ZnX2 .

Copper-Catalyzed Enantioselective Arylation via Radical-Mediated C-C Bond Cleavage: Synthesis of Chiral ω,ω-Diaryl Alkyl Nitriles

The first example of copper-catalyzed ring-opening, enantioselective arylation of cyclic ketoxime esters to access ω,ω-diaryl alkyl nitriles has been developed in high yield (up to 92% yield) with excellent enantioselectivity (up to 91% ee). Side-arm bis(oxazoline) ligand plays a significant role in this asymmetric catalytic transformation, which provides an efficient route to construct diverse chiral ω,ω-diaryl alkyl nitriles. Synthetic utility has also been demonstrated in the further derivatization of the ω,ω-diaryl alkyl nitrile to the corresponding amide.

Photocatalytic Redox-Neutral Approach to Diarylmethanes

We report a visible-light induced redox-neutral decarboxylative cross coupling reaction of indole-3-acetic acid NHPI esters with indoles using a Ru photosensitizer to deliver a wide range of symmetrical and unsymmetrical 3,3'-bisindolylmethane derivatives. Furthermore, the reaction is readily adapted to the preparation of a wide variety of diarylmethane derivatives.

Synthesis of Functionalized Aliphatic Acid Esters via the Generation of Alkyl Radicals from Silylperoxyacetals

We describe a catalytic method for the synthesis of a variety of functionalized aliphatic acid esters using silylperoxyacetals, which are versatile alkyl radical precursors with a terminal ester moiety. In the presence of an appropriate transition-metal catalyst, the in situ generation of alkyl radicals and the subsequent bond-forming process proceeds smoothly to afford synthetically valuable aliphatic acid derivatives. The present method can be applied to the efficient synthesis of a pharmaceutically important 1,1-diarylalkane motif. In addition, a novel strategy for the synthesis of structurally diverse hydroxy acid derivatives via a C-O bond formation process that utilizes TEMPO has been developed.

Nickel-Catalyzed Regioselective Alkenylarylation of γ,δ-Alkenyl Ketones via Carbonyl Coordination

We disclose a nickel-catalyzed reaction, which enabled us to difunctionalize unactivated γ,δ-alkenes in ketones with alkenyl triflates and arylboronic esters. The reaction was made feasible by the use of 5-chloro-8-hydroxyquinoline as a ligand along with NiBr2 ⋅DME as a catalyst and LiOtBu as base. The reaction proceeded with a wide range of cyclic, acyclic, endocyclic and exocyclic alkenyl ketones, and electron-rich and electron-deficient arylboronate esters. The reaction also worked with both cyclic and acyclic alkenyl triflates. Control experiments indicate that carbonyl coordination is required for the reaction to proceed.

Modular Synthesis of α-Quaternary Chiral β-Lactams by a Synergistic Copper/Palladium-Catalyzed Multicomponent Reaction

An asymmetric multicomponent, interrupted Kinugasa allylic alkylation (IKAA) reaction has been developed with a synergistic Cu-catalyzed Kinugasa system and a Pd-catalyzed allylic alkylation reaction. This unprecedented reaction provides in high yields and with high stereoselectivity a synthesis of α-quaternary chiral β-lactams, which cannot be produced with existing synthetic methods. Stereoselective coupling of two catalytic amounts of transient organometallic intermediates formed in situ is an important feature of this reaction.