Three-Component Olefin Dicarbofunctionalization Enabled by Nickel/Photoredox Dual Catalysis

Ni-Catalyzed Reductive 1,2-Alkylarylation of Alkenes for the Synthesis of Spirocyclic γ-Lactams

An intermolecular nickel-catalyzed reductive 1,2-alkylarylation of acrylates with cyclopropylamine NHP esters and aryl iodides is reported. This operationally simple protocol provides direct access to 1-alkylcyclopropylamine scaffolds. The mild conditions are compatible with four-membered α-amino strained rings as well as five- and six-membered ring systems. The products undergo cyclization to access α-arylated spirocyclic γ-lactams─a motif present in several pharmaceuticals.

Mechanochemical Synthesis of α-halo Alkylboronic Esters

α-halo alkylboronic esters, acting as ambiphilic synthons, play a pivotal role as versatile intermediates in fields like pharmaceutical science and organic chemistry. The sequential transformation of carbon-boron and carbon-halogen bonds into a broad range of carbon-X bonds allows for programmable bond formation, facilitating the incorporation of multiple substituents at a single position and streamlining the synthesis of complex molecules. Nevertheless, the synthetic potential of these compounds is constrained by limited reaction patterns. Additionally, the conventional methods often necessitate the use of bulk toxic solvents, exhibit sensitivity to air/moisture, rely on expensive metal catalysts, and involve extended reaction times. In this report, a ball milling technique is introduced that overcomes these limitations, enabling the external catalyst-free multicomponent coupling of aryl diazonium salts, alkenes, and simple metal halides. This approach offers a general and straightforward method for obtaining a diverse array of α-halo alkylboronic esters, thereby paving the way for the extensive utilization of these synthons in the synthesis of fine chemicals.

Catalytic tert-alkylation of enamides via C-C bond cleavage under photoredox conditions

Efficient C-C bond cleavage is recognized as a persistent challenge in the field of synthetic methodology. In this study, we found that tertiary alkyl radicals are smoothly formed from tertiary alkylated dienones (BHT adducts) via SET, using PDI as a photocatalyst. Resulting tert-alkyl radicals could be applied to the tert-alkylation of enamides. The driving force of this C-C bond cleavage reaction is the mesolytic cleavage of the BHT adducts. The mechanistic study revealed that PDI anion radical is the key active species during the catalytic cycle.

Nickel-catalysed enantioselective alkene dicarbofunctionalization enabled by photochemical aliphatic C-H bond activation

The development of novel strategies to rapidly construct complex chiral molecules from readily available feedstocks is a long-term pursuit in the chemistry community. Radical-mediated alkene difunctionalizations represent an excellent platform towards this goal. However, asymmetric versions remain highly challenging, and more importantly, examples featuring simple hydrocarbons as reaction partners are elusive. Here we report an asymmetric three-component alkene dicarbofunctionalization capitalizing on the direct activation of C(sp 3)-H bonds through the combination of photocatalysed hydrogen atom transfer and nickel catalysis. This protocol provides an efficient platform for installing two vicinal carbon-carbon bonds across alkenes in an atom-economic fashion, providing a wide array of high-value chiral α-aryl/alkenyl carbonyls and phosphonates, as well as 1,1-diarylalkanes from ubiquitous alkane, ether and alcohol feedstocks. This method exhibits operational simplicity, broad substrate scope and excellent regioselectivity, chemoselectivity and enantioselectivity. The compatibility with bioactive motifs and expedient synthesis of pharmaceutically relevant molecules highlight the synthetic potential of this protocol.

Palladium-Catalyzed Cascade Heck Coupling and Allylboration of Iododiboron Compounds via Diboryl Radicals

Geminal bis(boronates) are versatile synthetic building blocks in organic chemistry. The fact that they predominantly serve as nucleophiles in the previous reports, however, has restrained their synthetic potential. Herein we disclose the ambiphilic reactivity of α-halogenated geminal bis(boronates), of which the first catalytic utilization was accomplished by merging a formal Heck cross-coupling with a highly diastereoselective allylboration of aldehydes or imines, providing a new avenue for rapid assembly of polyfunctionalized boron-containing compounds. We demonstrated that this cascade reaction is highly efficient and compatible with various functional groups, and a wide range of heterocycles. In contrast to a classical Pd(0/II) scenario, mechanistic experiments and DFT calculations have provided strong evidence for a catalytic cycle involving Pd(I)/diboryl carbon radical intermediates.

A Bimolecular Homolytic Substitution-Enabled Platform for Multicomponent Cross-Coupling of Unactivated Alkenes

The construction of C(sp3)-C(sp3) bonds remains one of the most difficult challenges in cross-coupling chemistry. Here, we report a photoredox/nickel dual catalytic approach that enables the simultaneous formation of two C(sp3)-C(sp3) linkages via trimolecular cross-coupling of alkenes with alkyl halides and hypervalent iodine-based reagents. The reaction harnesses a bimolecular homolytic substitution (SH2) mechanism and chemoselective halogen-atom transfer (XAT) to orchestrate the regioselective addition of electrophilic and nucleophilic alkyl radicals across unactivated alkenes without the need for a directing auxiliary. Utility is highlighted through late-stage (fluoro)alkylation and (trideutero)methylation of C═C bonds bearing different substitution patterns, offering straightforward access to drug-like molecules comprising sp3-hybridized carbon scaffolds.

Computational Exploration of 1,2-Carboamine Carbonylation Catalyzed by Nickel

Nickel-catalyzed carbonylation of alkenes is a stereoselective and regioselective method for the synthesis of amide compounds. Theoretical predictions with density functional theory calculations revealed the mechanism and origin of stereoselectivity and regioselectivity for the nickel-catalyzed carbonylation of norbornene. The carbonylation reaction proceeds through oxidative addition, migration insertion of alkenes, and subsequent reduction elimination to afford cis-carbonylation product. The C-N bond activation of amides is unfavorable because the oxidative addition ability of the C-C bond is stronger than that of the C-N bond. The determining step of stereoselectivity is the migratory insertion of the strained olefin. The structural analysis shows that steroselectivity is controlled by the steric hindrance of methyl groups to olefins and substituents to IMes in ligands.

Reversible Radical Addition Guides Selective Photocatalytic Intermolecular Thiol-Yne-Ene Molecular Assembly

In modern organic chemistry, harnessing the power of multicomponent radical reactions presents both significant challenges and extraordinary potential. This article delves into this scientific frontier by addressing the critical issue of controlling selectivity in such complex processes. We introduce a novel approach that revolves around the reversible addition of thiyl radicals to multiple bonds, reshaping the landscape of multicomponent radical reactions. The key to selectivity lies in the intricate interplay between reversibility and the energy landscapes governing C-C bond formation in thiol-yne-ene reactions. The developed approach not only allows to prioritize the thiol-yne-ene cascade, dominating over alternative reactions, but also extends the scope of coupling products obtained from alkenes and alkynes of various structures and electron density distributions, regardless of their relative polarity difference, opening doors to more versatile synthetic possibilities. In the present study, we provide a powerful tool for atom-economical C-S and C-C bond formation, paving the way for the efficient synthesis of complex molecules. Carrying out our experimental and computational studies, we elucidated the fundamental mechanisms underlying radical cascades, a knowledge that can be broadly applied in the field of organic chemistry.

A free-radical design featuring an intramolecular migration for a synthetically versatile alkyl-(hetero)arylation of simple olefins

A free-radical approach has enabled the development of a synthetically versatile alkyl-(hetero)arylation of olefins. Alkyl and (hetero)aryl groups were added concurrently to a full suite of mono- to tetrasubstituted simple alkenes (i.e., without requiring directing or electronically activating groups) for the first time. Key advances also included the introduction of synthetically diversifiable alkyl groups featuring different degrees of substitution, good diastereocontrol in both cyclic and acyclic settings, the addition of biologically valuable heteroarenes featuring Lewis basic nitrogen atoms as well as simple benzenes, and the generation of either tertiary or quaternary benzylic centers. The synthetic potential of this transformation was demonstrated by leveraging it as the key step in a concise synthesis of oliceridine, a new painkiller that received FDA approval in 2020.

Nickel-Catalyzed Reductive Alkene Cross-Dialkylation with Unactivated Alkyl Electrophiles

A Ni-catalyzed reductive dialkylation of 8-aminoquinoline-tethered aliphatic alkenes with two unactivated alkyl electrophiles is disclosed here. Key to the development of this transformation is the combination of primary alkyl (pseudo)halides and secondary alkyl iodides that produce products in a single regioselective manner. The reaction exhibits good functional group compatibility, and its synthetic utility was demonstrated by the concise synthesis of the precursors of biologically relevant molecules.

Visible-Light-Induced Three-Component 1,2-Alkylpyridylation of Alkenes via a Halogen-Atom Transfer Process

Visible-light-induced three-component 1,2-alkylpyridylation of alkenes with unactivated alkyl iodides and aryl cyanides is reported via a photocatalytic halogen-atom transfer (XAT) strategy. This metal-free protocol utilizes readily available tertiary alkylamine as the terminal reductant to smoothly convert alkyl iodides into the corresponding carbon radical species. The reaction features a broad substrate scope, excellent functional group tolerance, high efficiency, and mild reaction conditions. The practicability of this methodology is further demonstrated in the late-stage difunctionalization of bioactive molecules.

Generation and Application of Homoallylic α,α-Diboryl Radicals via Diboron-Promoted Ring-Opening of Vinyl Cyclopropanes: cis-Diastereoselective Borylative Cycloaddition

Carbon-centered radicals stabilized by adjacent boron atoms are underexplored reaction intermediates in organic synthesis. This study reports the development of vinyl cyclopropyl diborons (VCPDBs) as a versatile source of previously unknown homoallylic α,α-diboryl radicals via thiyl radical catalyzed diboron-directed ring opening. These diboryl stabilized radicals underwent smooth [3+2] cycloaddition with a variety of olefins to provide diboryl cyclopentanes in good to excellent diastereoselectivity. In contrast to the trans-diastereoselectivity observed with most of the dicarbonyl activated VCPs, the cycloaddition of VCPDBs showed a remarkable preference for formation of cis-cyclopentane diastereomer which was confirmed by quantitative NOE and 2D NOESY studies. The cis-stereochemistry of cyclopentane products enabled a concise intramolecular Heck reaction approach to rare tricyclic cyclopentanoid framework containing the diboron group. The mild reaction conditions also allowed a one-pot VCP ring-opening, cycloaddition-oxidation sequence to afford disubstituted cyclopentanones. Control experiments and DFT analysis of reaction mechanism support a radical mediated pathway and provide a rationale for the observed diastereoselectivity. To the authors' knowledge, these are the first examples of the use of geminal diboryl group as an activator of VCP ring opening and cycloaddition reaction of α-boryl radicals.

Nickel/photoredox dual catalyzed arylalkylation of nonactivated alkenes

Alkene dicarbofunctionalization is an efficient strategy and operation-economic fashion for introducing complexity in molecules. A nickel/photoredox dual catalyzed arylalkylation of nonactivated alkenes for the simultaneous construction of one C(sp3)-C(sp3) bond and one C(sp3)-C(sp2) bond has been developed. The mild catalytic method provided valuable indanethylamine derivatives with wide substrate scope and good functional group compatibility. An enantioselective dicarbofunctionalization was also achieved with pyridine-oxazoline as a ligand. The efficiency of metallaphotoredox dicarbofunctionalization was demonstrated for the concise synthesis of pharmaceutically active compounds.

Iron-Catalyzed Enantioselective Multicomponent Cross-Couplings of α-Boryl Radicals

Despite recent interest in the development of iron-catalyzed transformations, methods that use iron-based catalysts capable of controlling the enantioselectivity in carbon-carbon cross-couplings are underdeveloped. Herein, we report a practical and simple protocol that uses commercially available and expensive iron salts in combination with chiral bisphosphine ligands to enable the regio- and enantioselective (up to 91:9) multicomponent cross-coupling of vinyl boronates, (fluoro)alkyl halides, and Grignard reagents. Preliminary mechanistic studies are consistent with rapid formation of an α-boryl radical followed by reversible radical addition to monoaryl bisphosphine-Fe(II) and subsequent enantioselective inner-sphere reductive elimination. From a broader perspective, this work provides a blueprint to develop asymmetric Fe-catalyzed multicomponent cross-couplings via the use of alkenes as linchpins to translocate alkyl radicals, modify their steric and electronic properties, and induce stereocontrol.

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.

Visible Light Induced Three-Component 1,2-Dicarbofunctionalization of Alkenes and Alkynes

Harnessing visible-light in organic synthesis is one of the most effective methods that aligns with green and sustainable chemistry principles and hence skyrocketed in the last two decades. Similarly, three-component 1,2-dicarbofunctionalization of alkenes and alkynes has recently been a great choice to construct complex molecular systems in an easy and rapid manner. Therefore, light-induced reactions can be an excellent alternative to carry out 1,2-dicarbofunctionalization reactions, and very recently, organic chemists across the globe have fascinated us with their interesting articles. In this present review, we have summarized the recent advancements in the area of visible light induced three-component 1,2-dicarbofunctionalization of alkenes and alkynes till March 2023. We have categorized the discussion based on the catalysts used to carry out the transformations for better understanding and different important aspects of these transformations have also been covered.

Photo-Triggered, Copper(II) Chloride-Catalyzed Radical Hydroalkylation and Hydrosilylation of Vinylboronic Esters To Access Alkylboronic Esters

Alkyl boronic acids and their derivatives constitute vital building blocks in organic synthesis and are important motifs identified in medicinal chemistry. Herein, we present a phototriggered, CuCl2-catalyzed radical hydroalkylation and hydrosilylation of vinylboronic esters to alkylboronic esters. This approach exhibits mild reaction conditions, utilization of easily accessible reagents, and scalability up to a gram scale. Further synthetic transformations of the hydrosilylation products and mechanistic studies are also demonstrated.

Visible-Light-Mediated Three-Component Decarboxylative Coupling Reactions to Synthesize 1,4-Diol Monoethers

An efficient approach for 1,2-difunctionalization of aromatic olefins and the synthesis of functionalized 1,4-diols monoethers has been established via a photoinduced three-component reaction of an α-alkoxycarboxylic acid, an aromatic olefin, and an aldehyde. The reaction proceeds by photoinduced oxidative decarboxylation of the carboxylic acid followed by the addition of the α-alkoxyalkyl radical to the olefin, one-electron reduction of the addition radical, and the nucleophilic attack of the resulting carbanion to the aldehyde. Besides the convenient one-pot protocol of the three-component reaction, this method offers several other advantages, including good functional group tolerance for the three substrates, gentle reaction conditions, and ease of scaling up. The reaction mechanism has been investigated through free radical trapping experiment and isotope labeling experiments.

Construction of α-Halogenated Boronic Esters via Visible Light-Induced C-H Bromination

α-Halogenated boronic esters are versatile building blocks that can be diversified into a wide variety of polyfunctionalized molecules. However, their synthetic potential has been hampered by limited preparation methods. Herein, we report a visible light-induced C-H bromination reaction of readily available benzyl boronic esters. This method features high yields, mild conditions, simple operation, and good functional group tolerance. The analogous chlorides and iodides can be accessed via Finkelstein reaction. Synthesis of halogenated geminal diborons has also been demonstrated.

Direct Light-Enabled Access to α-Boryl Radicals: Application in the Stereodivergent Synthesis of Allyl Boronic Esters

Operationally simple strategies to assemble boron containing organic frameworks are highly enabling in organic synthesis. While conventional retrosynthetic logic has engendered many platforms focusing on the direct formation of C-B bonds, α-boryl radicals have recently reemerged as versatile open-shell alternatives to access organoborons via adjacent C-C bond formation. Direct light-enabled α-activation is currently contingent on photo- or transition metal-catalysis activation to efficiently generate radical species. Here, we disclose a facile activation of α-halo boronic esters using only visible light and a simple Lewis base to enable homolytic scission. Intermolecular addition to styrenes facilitates the rapid construction of highly versatile E-allylic boronic esters. The simplicity of activation permits the strategic merger of this construct with selective energy transfer catalysis to enable the complimentary stereodivergent synthesis of Z-allylic boronic esters.

Rapid Synthesis of β-Chiral Sulfones by Ni-Organophotocatalyzed Enantioselective Sulfonylalkenylation of Alkenes

β-Chiral sulfones are substructures widespread in drug molecules and bioactive targets and serve as important chiral synthons in organic synthesis yet are challenging to access. Herein, a three-component strategy enabled by visible-light- and Ni-catalyzed sulfonylalkenylation of styrenes for the synthesis of enantioenriched β-chiral sulfones has been developed. This dual-catalysis strategy allows for one-step skeletal assembly along with the control of enantioselectivity in the presence of a chiral ligand, providing an efficient and straightforward access to enantioenriched β-alkenyl sulfones from easily available and simple starting materials. Mechanistic investigations reveal that the reaction undergoes a chemoselective radical addition over two alkenes followed by a Ni-intercepted asymmetric C_sp³-C_sp² coupling with alkenyl halides.

Recovery of homogeneous photocatalysts by covalent organic framework membranes

Transition metal-based homogeneous photocatalysts offer a wealth of opportunities for organic synthesis. The most versatile ruthenium(II) and iridium(III) polypyridyl complexes, however, are among the rarest metal complexes. Moreover, immobilizing these precious catalysts for recycling is challenging as their opacity may obstruct light transmission. Recovery of homogeneous catalysts by conventional polymeric membranes is promising but limited, as the modulation of their pore structure and tolerance of polar organic solvents are challenging. Here, we report the effective recovery of homogeneous photocatalysts using covalent organic framework (COF) membranes. An array of COF membranes with tunable pore sizes and superior organic solvent resistance were prepared. Ruthenium and iridium photoredox catalysts were recycled for 10 cycles in various types of photochemical reactions, constantly achieving high catalytical performance, high recovery rates, and high permeance. We successfully recovered the photocatalysts at gram-scale. Furthermore, we demonstrated a cascade isolation of an iridium photocatalyst and purification of a small organic molecule product with COF membranes possessing different pore sizes. Our results indicate an intriguing potential to shift the paradigm of the pharmaceutical and fine chemical synthesis campaign.

Photocatalyzed regioselective hydrosilylation for the divergent synthesis of geminal and vicinal borosilanes

Geminal and vicinal borosilanes are useful building blocks in synthetic chemistry and material science. Hydrosilylation/hydroborylation of unsaturated systems offer expedient access to these motifs. In contrast to the well-established transition-metal-catalyzed methods, radical approaches are rarely explored. Herein we report the synthesis of geminal borosilanes from α-selective hydrosilylation of alkenyl boronates via photoinduced hydrogen atom transfer (HAT) catalysis. Mechanistic studies implicate that the α-selectivity originates from a kinetically favored radical addition and an energetically favored HAT process. We further demonstrate selective synthesis of vicinal borosilanes through hydrosilylation of allyl boronates via 1,2-boron radical migration. These strategies exhibit broad scopes across primary, secondary, and tertiary silanes and various boron compounds. The synthetic utility is evidenced by access to multi-borosilanes in a diverse fashion and scaling up by continuous-flow synthesis.

Photocatalytic Alkyl Radical Addition Tandem Oxidation of Alkenyl Borates

Photocatalytic oxidation is a popular transformation way for organic synthesis and is widely applied in academia and industry. Herein, we report a blue light-induced alkylation-oxidation tandem reaction for the synthesis of diverse ketones by combining alkyl radical addition and oxidation of alkenyl borates. This reaction shows excellent functional group compatibility in acceptable yields, and diversity of radical precursors is applicable.

General Method for Selective Three-Component Carboacylation of Alkenes via Visible-Light Dual Photoredox/Nickel Catalysis

A photoredox/nickel dual catalytic protocol for the regioselective three-component carboacylation of alkenes with tertiary and secondary alkyltrifluoroborates as well as acyl chlorides is described. This redox-neutral protocol can be applied to the rapid synthesis of ketones with high diversity and complexity via a radical relay process. Many functional groups, allowing for various commercially available acyl chlorides, alkyltrifluoroborates, and alkenes, are tolerated under these mild conditions.

Photoredox-Mediated Deoxygenative Radical Additions of Aromatic Acids to Vinyl Boronic Esters and gem-Diborylalkenes

A new method to access β-keto-gem-diborylalkanes, by direct deoxygenative radical addition of aromatic carboxylic acids to gem-dibortlalkenes, is described. The reaction proceeds under mild photoredox catalysis and involves the photochemical C-O bond activation of aromatic carboxylic acids in the presence of PPh₃ . It generates an acyl radical, which further undergoes an additional reaction with gem-diborylalkenes to form an α-gem-diboryl alkyl radical intermediate, which then reduces to the corresponding anion, which after protonation, affords the β-keto-gem-diborylalkane product. Moreover, the same scenario has been extended to the vinyl boronic esters, for example, gem-(Ar, Bpin)-alkenes, and gem-(Alkyl, Bpin)-alkenes. Importantly, this protocol provides a general platform for the late-stage functionalization of bio-active and drug molecules containing a carboxylic acid group.

One step synthesis of unsymmetrical 1,3-disubstituted BCP ketones via nickel/photoredox-catalyzed [1.1.1]propellane multicomponent dicarbofunctionalization

Bicyclo[1.1.1]pentanes (BCPs), utilized as sp3-rich bioisosteres for tert-butyl- and aryl groups as well as internal alkynes, have gained considerable momentum in drug development programs. Although many elegant methods have been developed to access BCP amines and BCP aryls efficiently, the methods used to construct BCP ketones directly are relatively underdeveloped. In particular, the preparation of unsymmetrical 1,3-disubstituted-BCP ketones remains challenging and still requires multiple chemical steps. Herein, a single-step, multi-component approach to versatile disubstituted BCP ketones via nickel/photoredox catalysis is reported. Importantly, installing a boron group at the carbon position adjacent to the BCP structure bypasses the limitation to tertiary BF3K coupling partners, thus expanding the scope of this paradigm. Further transformation of disubstituted-BCP ketones into a variety of other BCP derivatives demonstrates the synthetic value of this developed method.

Photoinduced Three-Component Carboarylation of Unactivated Alkenes with Protic C(sp3)-H Feedstocks

A general and mild strategy involving three-component carboarylation of unactivated alkenes with protic C(sp³)-H feedstocks via photoredox catalysis was reported. This catalytic system is compatible with a broad range of unactivated alkenes, cyano-substituted arenes, and diverse protic C(sp³)-H feedstocks. The synthetic value of this protocol was demonstrated by the late-stage functionalization of complex molecules and the synthesis of the antiallergies including pheniramine, chlorpheniramine, and brompheniramine.

The Impact of Boron Hybridisation on Photocatalytic Processes

Recently the fruitful merger of organoboron chemistry and photocatalysis has come to the forefront of organic synthesis, resulting in the development of new technologies to access complex (non)borylated frameworks. Central to the success of this combination is control of boron hybridisation. Contingent on the photoactivation mode, boron as its neutral planar form or tetrahedral boronate can be used to regulate reactivity. This Minireview highlights the current state of the art in photocatalytic processes utilising organoboron compounds, paying particular attention to the role of boron hybridisation for the target transformation.

Exploiting the sp2 character of bicyclo[1.1.1]pentyl radicals in the transition-metal-free multi-component difunctionalization of [1.1.1]propellane

Strained bicyclic substructures are increasingly relevant in medicinal chemistry discovery research because of their role as bioisosteres. Over the last decade, the successful use of bicyclo[1.1.1]pentane (BCP) as a para-disubstituted benzene replacement has made it a highly valuable pharmacophore. However, various challenges, including limited and lengthy access to useful BCP building blocks, are hampering early discovery research. Here we report a single-step transition-metal-free multi-component approach to synthetically versatile BCP boronates. Radicals derived from commonly available carboxylic acids and organohalides perform additions onto [1.1.1]propellane to afford BCP radicals, which then engage in polarity-matched borylation. A wide array of alkyl-, aryl- and alkenyl-functionalized BCP boronates were easily prepared. Late-stage functionalization performed on natural products and approved drugs proceeded with good efficiency to generate the corresponding BCP conjugates. Various photoredox transformations forging C-C and C-N bonds were demonstrated by taking advantage of BCP trifluoroborate salts derived from the BCP boronates.

The Merger of Benzophenone HAT Photocatalysis and Silyl Radical-Induced XAT Enables Both Nickel-Catalyzed Cross-Electrophile Coupling and 1,2-Dicarbofunctionalization of Olefins

A strategy for both cross-electrophile coupling and 1,2-dicarbofunctionalization of olefins has been developed. Carbon-centered radicals are generated from alkyl bromides by merging benzophenone hydrogen atom transfer (HAT) photocatalysis and silyl radical-induced halogen atom transfer (XAT) and are subsequently intercepted by a nickel catalyst to forge the targeted C(sp³)–C(sp²) and C(sp³)–C(sp³) bonds. The mild protocol is fast and scalable using flow technology, displays broad functional group tolerance, and is amenable to a wide variety of medicinally relevant moieties. Mechanistic investigations reveal that the ketone catalyst, upon photoexcitation, is responsible for the direct activation of the silicon-based XAT reagent (HAT-mediated XAT) that furnishes the targeted alkyl radical and is ultimately involved in the turnover of the nickel catalytic cycle.

A three-component difunctionalization of N-alkenyl amides via organophotoredox radical-polar crossover

Herein, we report a three-component organophotoredox coupling of N-alkenyl amides with α-bromocarbonyls and various nucleophiles. This transition metal-free difunctionalization protocol installs sequential C-C and C-Y (Y = S/O/N) bonds in alkenes. This reaction works with terminal and internal alkenes containing both cyclic and acyclic amides via radical-polar crossover.

Dicarbofunctionalization of [1.1.1]Propellane Enabled by Nickel/Photoredox Dual Catalysis: One-Step Multicomponent Strategy for the Synthesis of BCP-Aryl Derivatives

Bicyclo[1.1.1]pentane (BCP) motifs as para-disubstituted aryl bioisosteres are playing an emerging role in pharmaceutical, agrochemical, and materials chemistry. The vast majority of these structures is obtained from a BCP electrophile or nucleophile, which are themselves derived from [1.1.1]propellane via cleavage of the internal C-C bond through the addition of either radicals or metal-based nucleophiles. Compared with the current stepwise approaches, a multicomponent reaction that provides direct access to complex and diverse disubstituted BCP products would be more attractive. Herein, we report a single-step, multicomponent approach to synthetically versatile arylated BCP products via nickel/photoredox catalysis. Importantly, this three-component process allows two C-C bonds to be formed in a single step and sets three quaternary centers, unprecedented in any previously reported methods. The method has been demonstrated to allow access to complex BCP architectures from aryl halide and radical precursor substrates.

From Styrenes to Fluorinated Benzyl Bromides: A Photoinduced Difunctionalization via Atom Transfer Radical Addition

An operationally simple and practical method is disclosed to achieve the difunctionalization of styrenes, generating fluorinated benzyl bromides via a photoinduced atom transfer radical addition process. The developed method is mild, atom-economical, cost-effective, employs very low photocatalyst loading (1000 ppm), and is highly compatible with a broad range of functional groups on styrene. The versatility of the fluorinated benzyl bromides is demonstrated through their derivatization to a variety of valuable compounds.

IrIII/NiII-Metallaphotoredox-Catalyzed Enantioselective Decarboxylative Arylation of α-Amino Acids: Theoretical Insight of Enantio-Determining Outer-Sphere Reductive Elimination

The Ir^III/Ni^II-metallaphotoredox-catalyzed enantioselective decarboxylative arylation of α-amino acids has been systematically investigated using density functional theory calculations. The combination of oxidative quenching (Ir^III-*Ir^III-Ir^IV-Ir^III) or reductive quenching (Ir^III-*Ir^III-Ir^II-Ir^III) cycle with the nickel catalytic cycle (Ni^II-Ni^I-Ni^III-Ni^II) is possible. The favorable reaction mechanism consists of three major processes: single-electron transfer, oxidative addition, and stepwise outer-sphere reductive elimination. The rate-determining step is the oxidative addition. Unexpectedly, the enantio-determining C-C bond formation occurs via an ion-pair intermediate involved in the stepwise outer-sphere reductive elimination process, which is unusual in the Ir^III/Ni^II-metallaphotoredox catalysis. Furthermore, computational results reveal that the high enantioselectivity of this reaction is mainly dependent on the steric effect of substituents on substrates. This theoretical study provides useful knowledge for deep insights into the activity and selectivity of visible-light-mediated enantioselective metallaphotoredox dual catalysis at the molecular and atomic levels and benefits the development of asymmetric synthesis.

Ni-Catalyzed Regio- and Stereoselective Alkylarylation of Unactivated Alkenes in γ,δ-Alkenylketimines

We disclose a Ni-catalyzed vicinal alkylarylation of unactivated alkenes in γ,δ-alkenylketimines with aryl halides and alkylzinc reagents. The reaction produces γ-C(sp3)-branched δ-arylketones with the construction of two new C(sp3)-C(sp3) and C(sp3)-C(sp2) bonds. Electron-deficient alkenes play crucial dual roles as ligands to stabilize reaction intermediates and to increase catalytic rates for the formation of C(sp3)-C(sp3) bonds. This alkene alkylarylation reaction is also effective for secondary alkylzinc reagents and internal alkenes, and proceeds with a complete regio- and stereocontrol, affording products with up to three contiguous all-carbon all-cis secondary stereocenters.

ART─An Amino Radical Transfer Strategy for C(sp2)-C(sp3) Coupling Reactions, Enabled by Dual Photo/Nickel Catalysis

Introducing the novel concept of amino radical transfer (ART) enables the use of easily accessible and commercially available alkyl boronic esters as cross-coupling partners for aryl halides in dual photoredox/nickel catalysis mediated by visible light. Activation of otherwise photochemically innocent boronic esters by radicals generated from primary or secondary alkylamines gives rise to an outstanding functional group tolerance in a mild, fast, and air-stable reaction. As shown in more than 50 examples including unprotected alcohols, amines, and carboxylic acids, this reaction allows quick access to relevant scaffolds for organic synthesis and medicinal chemistry. In comparison with existing methods for C(sp²)-C(sp³) couplings an extraordinary generality could be realized via the ART concept, employing a single set of optimized reaction conditions. Due to its selectivity, the transformation can also be used for late-stage functionalization, as demonstrated with three exemplary syntheses of drug molecules. Furthermore, the successful one-to-one scalability of this reaction up to gram scale without the necessity of any further precautions or flow systems is demonstrated.

Nickel-Catalyzed Three-Component Alkylacylation of Alkenes Enabled by a Photoactive Electron Donor-Acceptor Complex

An electron donor-acceptor complex-enabled, nickel-catalyzed three-component net-reductive 1,2-alkylacylation of alkenes is developed. This conjunctive reductive acyl cross-coupling process obviates the use of an exogenous photocatalyst and a stoichiometric metal-based reductant, affording various synthetically useful 1,3-dicarbonyl compounds in good yields with a broad substrate scope and excellent functional group tolerance. Both alkyl and acyl electrophiles are derived from the highly abundant and readily accessible carboxylic acids, making the catalytic 1,2-dicarbofunctionalization more synthetically general and sustainable.

Ni-Catalyzed Reductive 1,2-Cross-Dialkylation of Unactivated Alkenes with Two Alkyl Bromides

Cross-dialkylation of unactivated alkenes represents a significant challenge due to competitive β-hydride elimination and associated selectivity issues. Herein, a Ni-catalyzed reductive 1,2-dialkylation of unactivated aliphatic alkenes has been developed using two different alkyl bromides. The reaction proceeds smoothly under mild conditions to install two C_sp3-C_sp3 bonds onto directed aliphatic alkenes, demonstrating excellent chemo- and regioselectivity with good functional group tolerance.