Enantioselective Trifluoromethylalkynylation of Alkenes via Copper-Catalyzed Radical Relay

Building trisubstituted ethylenes from terminal alkenes via debrominative ring-opening trifluoromethylations of geminal dibromocyclopropanes

CuI-catalyzed regio- and stereoselective dehalogenative ring-opening trifluoromethylations of geminal dibromo- or dichlorocyclopropanes or monobromocyclopropanes delivered stereodefined trisubstituted or disubstituted ethylenes bearing a CH2CF3 group in good yields. Purple light-promoted reductive monodebromination of gem-dibromocyclopropanes was also developed.

Metallaphotoredox-catalyzed alkynylcarboxylation of alkenes with CO2 and alkynes for expedient access to β-alkynyl acids

Carboxylation with CO2 offers an attractive and sustainable access to valuable carboxylic acids. Among these methods, direct C-H carboxylation of terminal alkynes with CO2 has attracted much attention for one-carbon homologation of alkynes, enabling rapid synthesis of propiolic acids. In contrast, the multi-carbons homologation of alkynes with CO2 to construct important non-conjugated alkynyl-containing acids has not been reported. Herein, we present alkynylcarboxylation of alkenes with CO2 via photoredox and copper dual catalysis. This protocol provides a direct and practical method to form valuable non-conjugated alkynyl acids from readily available alkynes, alkenes and CO2. Additionally, this approach also features mild (room temperature, 1 atm of CO2) and redox-neutral conditions, high atom and step economy, good functional group tolerance, and high selectivities. Moreover, diverse transformations of the β-alkynyl acid products and the rapid synthesis of bioactive molecule (GPR40/FFA1 agonist) further illustrate the synthetic utility of this methodology.

Enantioselective Photoredox- and Cu-Catalyzed Cyanoalkylation of Styrenes via Deoxygenation of Alkoxyl Radicals with Organophosphorus Compounds(III)

The enantioselective cyanoalkylation of styrenes by a cooperative photoredox and copper catalysis system has been established, providing straightforward access to structurally diverse enantioenriched alkyl nitriles in good yields with excellent enantioselectivities under mild conditions via deoxygenation of alkoxyl radicals with organophosphorus compounds(III). In addition, the reaction features a wide substrate scope and good functional group tolerance, and the resultant alkyl nitriles could be easily converted into a series of chiral carboxylic acids, amides, esters, etc.

Inverse conjugate additions of acrylic amides and esters with F/Cl/O/N-nucleophiles and CF3+ reagents

The conjugate additions of nucleophiles to conjugate acceptors are among the most powerful hetero-carbon bond formation reactions. The conjugate addition normally occurs via a β-nucleophilic addition, resulting in the formation of a stabilized α-carbanion intermediate that can be subsequently quenched by electrophiles or protons. Nevertheless, the inverse conjugate addition involving an α-specific nucleophilic addition remains less explored because of the electronic mismatch. In this research, we disclosed an α-specific nucleophilic addition of the nucleophiles including Py·HF, TBACl, HOR, H2O, H218O, RCO2H, and pyrazole to conjugate acceptors concurrent with a trifluoromethylation. This umpolung and inversely regioselective conjugate addition, enabled by a visible light-induced redox photocatalysis, occurred via an unusual α-nucleophilic addition other than the normal β-nucleophilic addition to efficiently generate diverse α-functionalized CF3-containing amides/esters. The broad substrate scope, excellent functional-group tolerance, and versatile late-stage derivatizations as well as the biologically and functionally important CF3-containing products demonstrated the potential applications of this protocol in materials, agrochemicals, and pharmaceutical chemistry.

Copper-Catalyzed Asymmetric Tertiary Radical Cyanation for the Synthesis of Chiral Tetrasubstituted Monofluoroacyl Nitriles

The construction of chiral tetrasubstituted α-fluoro-α-cyano carbonyl compounds remains a key challenge in synthetic organic chemistry because of their popularity in multiple disciplines. In this paper, we report the copper-catalyzed asymmetric fluorinated tertiary radical cyanation reaction of cyclic α-iodo-α-fluoroindanones with TMSCN to achieve chiral nitriles with carbon-fluorine quaternary stereogenic centers. Thus, an array of optically active tetrasubstituted monofluoroacyl nitriles were synthesized with high reaction efficiency and excellent enantioselectivities (up to 91% yield, 99% ee). Moreover, mechanistic investigations, including experiments, were conducted to clarify the reaction pathway and stereochemical outcomes.

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.

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.

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Nickel-Catalyzed Three-Component 1,2-Carboacylation of Alkenes

Ketones, prevalent in many biologically significant molecules, require the development of novel methods to synthesize these structures, which is a critical endeavor in organic synthesis. Transition metal catalysis has proven to be an effective method for synthesizing ketones. However, the scope of these substrates remains relatively limited, particularly due to their incompatibility with sensitive functional groups. Herein, we report a Ni-catalyzed three-component 1,2-carboacylation of alkenes, which activates secondary/tertiary alkyl bromides. This method offers significant advantages: simplicity of operation, ready availability of substrates, and broad substrate applicability. A series of experimental studies have helped clarify the key mechanistic pathways involved in this cascade reaction.

Red-light-mediated copper-catalyzed photoredox catalysis promotes regioselectivity switch in the difunctionalization of alkenes

Controlling regioselectivity during difunctionalization of alkenes remains a significant challenge, particularly when the installation of both functional groups involves radical processes. In this aspect, methodologies to install trifluoromethane (-CF3) via difunctionalization have been explored, due to the importance of this moiety in the pharmaceutical sectors; however, these existing reports are limited, most of which affording only the corresponding β-trifluoromethylated products. The main reason for this limitation arises from the fact that -CF3 group served as an initiator in those reactions and predominantly preferred to be installed at the terminal (β) position of an alkene. On the contrary, functionalization of the -CF3 group at the internal (α) position of alkenes would provide valuable products, but a meticulous approach is necessary to win this regioselectivity switch. Intrigued by this challenge, we here develop an efficient and regioselective strategy where the -CF3 group is installed at the α-position of an alkene. Molecular complexity is achieved via the simultaneous insertion of a sulfonyl fragment (-SO2R) at the β-position. A precisely regulated sequence of radical generation using red light-mediated photocatalysis facilitates this regioselective switch from the terminal (β) position to the internal (α) position. Furthermore, this approach demonstrates broad substrate scope and industrial potential for the synthesis of pharmaceuticals under mild reaction conditions.

Three-Component Radical Cross-Coupling: Asymmetric Vicinal Sulfonyl-Esterification of Alkenes Involving Sulfur Dioxide

A novel catalytic system for radical cross-coupling reactions based on copper and chiral Pyridyl-bis(imidazole) (PyBim) ligands is described. It overcomes the challenges of chemoselectivity and enantioselectivity, achieving a highly enantioselective vicinal sulfonyl-esterification reaction of alkenes involving sulfur dioxide. This strategy involves the use of earth-abundant metal catalyst, mild reaction conditions, a broad range of substrates (84 examples), high yields (up to 97% yield), and exceptional control over enantioselectivity. The reaction system is compatible with different types of radical precursors, including O-acylhydroxylamines, cycloketone oxime esters, aryldiazonium salts, and drug molecules. Chiral ligand PyBim is identified as particularly effective in achieving the desired high enantioselectivity. Mechanistic studies reveal that copper/PyBim system plays a vital role in C─O coupling, employing an outer-sphere model. In addition, the side arm effect of ligand is observed.

CuCl2/FeCl3 Bimetallic Photocatalyst for Sustainable Ethylene Production from Ethanol via Recoverable Redox Cycles

Photocatalytic conversions of ethanol to valuable chemicals are significant organic synthesis reactions. Herein, we developed a CuCl2/FeCl3 bimetallic photocatalyst for sustainable dehydration of ethanol to ethylene by recoverable redox cycles. The selectivity of ethylene was 98.3% for CuCl2/FeCl3, which is much higher than that of CuCl2 (34.5%) and FeCl3 (86.5%). Due to the ligand-to-metal charge transfer (LMCT) process involved in generating the liquid products, the CuCl2/FeCl3 catalyst will be reduced to CuCl/FeCl2. Oxygen (O2) is required for the recovery of CuCl2/FeCl3 to avoid exhaustion. The soluble Fe3+/Fe2+ redox species deliver catalyst regeneration properties more efficiently than single metal couples, making a series of redox reactions (Cu2+/Cu+, Fe3+/Fe2+, and O2/ethanol couples) recyclable with synergistic effects. A flow reactor was designed to facilitate the continuous production of ethylene. The understanding of bimetallic synergism and consecutive reactions promotes the industrial application process of photocatalytic organic reactions.

Dehydrative alkynylation of 3-hydroxyisoindolinones with terminal alkynes for the synthesis of 3-alkynylated 3,3-disubstituted isoindolinones

A brand-new procedure for the synthesis of 3-alkynylated 3,3-disubstituted isoindolinones has been disclosed via a HOTf or Fe(OTf)3-catalyzed dehydrative alkynylation of 3-hydroxyisoindolinones with terminal alkynes. Aryl, alkenyl and alkyl terminal alkynes are suitable to couple with a broad range of 3-hydroxyisoindolinones to afford the desired products in moderate to good yields. This protocol features the use of an inexpensive catalyst, mild reaction conditions, broad substrate scope and easy elaboration of the products.

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.

Nickel-Catalyzed Asymmetric Propargyl-Aryl Cross-Electrophile Coupling

Performing asymmetric cross-coupling reactions between propargylic electrophiles and aryl nucleophiles is a well-established method to build enantioenriched benzylic alkynes. Here, a catalytic enantioselective propargyl-aryl cross-coupling between two electrophiles was achieved for the first time in a stereoconvergent manner. Propargylic chlorides were treated with aryl iodides as well as heteroaryl iodides in the presence of a chiral nickel complex, and manganese metal was used as a stoichiometric reductant, allowing for the construction of a propargyl C-aryl bond under mild conditions. An alternative dual nickel/photoredox catalytic protocol was also developed for this cross-electrophile coupling in the absence of a metal reductant. The potential utility of this conversion is demonstrated in the facile construction of stereoenriched bioactive molecule derivatives and medicinal compounds based on the diversity of acetylenic chemistry. Detailed experimental studies have revealed the key mechanistic features of this transformation.

Transition-metal-catalyzed atroposelective synthesis of axially chiral styrenes

Axially chiral styrenes, a type of atropisomer analogous to biaryls, have attracted great interest because of their unique presence in natural products and asymmetric catalysis. Since 2016, a number of methodologies have been developed for the atroposelective construction of these chiral skeletons, involving both transition metal catalysis and organocatalysis. In this feature article, we aim to provide a comprehensive understanding of recent advances in the asymmetric synthesis of axially chiral styrenes catalyzed by transition metals, integrating scattered work with different catalytic systems together. This feature article is cataloged into five sections according to the strategies, including asymmetric coupling, enantioselective C-H activation, central-to-axial chirality transfer, asymmetric alkyne functionalization, and atroposelective [2+2+2] cycloaddition.

Copper-Catalyzed Enantioselective Difluoromethylation-Alkynylation of Olefins by Solving the Dilemma between Acidities and Reduction Potentials of Difluoromethylating Agents

Molecules containing a difluoromethyl group or a propargylic stereocenter are widely used in pharmaceuticals and agrochemicals, and 1,2-functionalization of olefins is an important method for introducing the two groups into molecules simultaneously. The construction of the propargylic stereocenter with terminal alkynes usually requires bases. However, difluoromethylating agents with high reduction potentials often decompose in the presence of bases because of their acidities, and those with low reduction potentials are stable but difficult to undergo the desired single electron transfer (SET) reduction. Using the linear relationship between reduction potential differences (ΔE) and Hammett substituent constants (σ) of difluoromethyl aryl sulfones, we solved the dilemma between acidities and reduction potentials of difluoromethylating agents. Herein, we report the first enantioselective difluoromethylation-alkynylation of olefins with difluoromethyl 4-chlorophenyl sulfone with high enantioselectivity (>90 % ee). We also extended this asymmetric fluoroalkylation-alkynylation reaction with other fluoroalkyl sulfones, which enabled efficient installation of trifluoromethyl, difluoroalkyl, difluorobenzyl, (benzenesulfonyl)-difluoromethyl and monofluoromethyl groups into products.

Methodological Development and Applications of Tryptamine-Ynamide Cyclizations in Synthesizing Core Skeletons of Indole Alkaloids

Over the past two decades, synthetic strategies for synthesizing the skeletons of various indole alkaloids based on tryptamine-ynamide have been continuously developed and applied to the total syntheses or formal total syntheses of related molecules. In this synopsis, we summarized the cyclization pathways of tryptamine-ynamide under different catalytic conditions, emphasizing the reaction mechanism and applications in the syntheses of indole alkaloids.

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.

Enantioselective Copper-Catalyzed Fukuyama Indole Synthesis from 2-Vinylphenyl Isocyanides

Enantioenriched chiral indoles are of high interest for the pharmaceutical and agrochemical industries. Herein, we present an asymmetric Fukuyama indole synthesis through a mild and efficient radical cascade reaction to access 2-fluoroalkylated 3-(α-cyanobenzylated) indoles by stereochemical control with a chiral copper-bisoxazoline complex using 2-vinylphenyl arylisocyanides as radical acceptors and fluoroalkyl iodides as C-radical precursors. Radical addition to the isonitrile moiety, 5-exo-trig cyclization, and Cu-catalyzed stereoselective cyanation provide the targeted indoles with excellent enantioselectivity and good yields. Due to the similar electronic and steric properties of the two aryl substituents to be differentiated, the enantioselective construction of the cyano diaryl methane stereocenter is highly challenging. Mechanistic studies reveal a negative nonlinear effect which allows proposing a model to explain the stereochemical outcome. Scalability and potential utility of the enantioenriched 3-(α-cyanobenzylated) indoles as hubs for chiral tryptamines, indole-3-acetic acid derivatives, and triarylmethanes are demonstrated, and a formal synthesis of a natural product analogue is disclosed.

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.

Deaminative Arylation and Alkenyaltion of Aliphatic Tertiary Amines with Aryl and Alkenylboronic Acids via Nitrogen Ylides

Transition-metal-catalyzed Suzuki-Miyaura coupling has significantly advanced C-C bond formation and has been well recognized in organic synthesis, pharmaceuticals, materials science and other fields. In this rapid development, cross coupling without transition metal catalyst is a big challenge in this field, and using widely existing tertiary amines as electrophiles to directly couple with boronic acids has great hurdles yet significant application prospects. Herein, we report an efficient and general deaminative arylation and alkenylation of tertiary amines (propargyl amines, allyl amines and 1H-indol-3-yl methane amines) with ary and alkenylboronic acids enabled by difluorocarbene under transition-metal-free conditions. Preliminary mechanism experiments suggest that in situ formed difluoromethyl quaternary amine salt, nitrogen ylide and tetracoordinate boron species are the key intermediates, the subsequent 1,2-metallate shift and protodeboronation complete the new coupling reaction.

Synthesis of β-Polychlorinated Alkynes Enabled by Copper-Catalyzed Multicomponent Reaction

Functional molecules bearing polychlorinated moieties usually play versatile roles in organic synthesis and biochemistry. A copper-catalyzed multicomponent polychloro-carboalkynylation of alkenes presents an efficient and operationally simple approach for the synthesis of β-polychlorinated alkynes. Mechanistic experiments were conducted demonstrating that an in situ generated copper acetylide complex was the real catalyst and reactive intermediate during the copper-catalytic cycle. And enantioselective exploration demonstrated potential application for the synthesis of chiral β-polychlorinated alkynes.

Developments in the Alkynyltrifluoromethylations of Alkenes and Alkynes

As a consequence of the expanding relevance of fluorine-containing organic molecules in drug research, the synthesis of organofluorine scaffolds has high significance in synthetic organic chemistry. Trifluoromethylative difunctionalizations of carbon–carbon multiple bonds, with the simultaneous introduction of a CF3 group and another function, have considerable potential. Considering the high importance of carbon–carbon bond-forming reactions in organic synthesis, carbotrifluoromethylations and, in particular, alkynyltrifluoromethylations have increasing interest in synthetic chemistry. Alkynyltrifluoromethylation is a narrow area and a relatively new approach in synthetic chemistry­; however it has not been reviewed so far. Our goal in this short review is to summarize recent developments in alkynyltrifluoromethylation reactions by considering: (a) alkynyltrifluoromethylation reactions of alkenes, including reactions involving either intramolecular alkynyl migration or intermolecular transformation, and (b) alkynyltrifluoromethylation reactions of alkynes.

1 Introduction

2 Alkynyltrifluoromethylation Reactions of Alkenes

2.1 Reactions Involving Intramolecular Alkynyl Migration

2.2 Intermolecular Reactions

3 Alkynyltrifluoromethylation Reactions of Alkynes

4 Summary and Outlook

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.

Enantioselective Copper-Catalyzed Intermolecular Cyanobenzoyldifluoromethylation of Alkenes: Access to Chiral β-Difluoroacyl Nitriles

A novel asymmetric copper-catalyzed intermolecular cyanobenzoyldifluoromethylation of alkenes with iododifluoromethyl ketones and TMSCN has been reported, which provides a particularly valuable route to access chiral β-difluoroacyl nitriles with excellent enantioselectivities. The method permits the efficient cyanation of varied β-difluoroacyl-benzylic radicals in mild conditions with high functional group tolerance. The reaction proceeds through a radical pathway. In order to get insight into the stereochemical outcome, computational mechanistic studies were conducted.

Palladium-catalyzed intermolecular alkynylcarbonylation of unactivated alkenes: easy access to β-alkynylcarboxylic esters

A palladium-catalyzed intermolecular alkynylcarbonylation of unactivated alkenes has been established with ethynyl benziodoxolones (EBXs) as alkynylation reagents, providing β-alkynylcarboxylic esters efficiently from simple alkenes. The reaction features moderate to excellent regioselectivity and excellent functional group compatibility under mild reaction conditions.

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.

Copper-Catalysed Synthesis of Trifluoromethyl Allenes via Fluoro-carboalkynylation of Alkenes

Allenes and trifluoromethyl motifs are considered as important building blocks in materials and pharmaceuticals. A copper-catalysed synthesis of trifluoromethyl allenes utilizing readily available feedstocks under mild and environmentlly friendly conditions...

Copper-Catalyzed 1,2-Trifluoromethylation Carbonylation of Unactivated Alkenes: Efficient Access to β-Trifluoromethylated Aliphatic Carboxylic Acid Derivatives

A novel copper-catalyzed carbonylative trifluoromethylation of unactivated alkenes has been developed. A broad range of β-trifluoromethylated carboxylic acid derivatives were prepared in moderate to excellent yields from simple alkenes with excellent regioselectivity. It is noteworthy that ethylene gas, as the simplest olefin, can also be applied directly to obtain β-trifluoromethylated amides and ester. This transformation presents the first example on carbonylative trifluoromethylation of alkenes.

Pd/GF-Phos-Catalyzed Asymmetric Three-Component Coupling Reaction to Access Chiral Diarylmethyl Alkynes

Significant attention has been given in the past few years to the selective transformations of N-tosylhydrazones to various useful compounds. However, the development of enantioselective versions poses considerable challenges. Herein we report a Pd-catalyzed enantioselective three-component coupling of N-tosylhydrazone, aryl halide, and terminal alkyne under mild conditions utilizing a novel chiral sulfinamide phosphine ligand (GF-Phos), which provides a facile access to chiral diarylmethyl alkynes, which are useful synthons in organic synthesis as well as exist as the skeleton in many bioactive molecules. A pair of enantiomers of the product could be easily prepared using the same chiral ligand by simply changing the aryl substituents of the N-tosylhydrazone and aryl halide. The salient features of this reaction include the readily available starting materials, general substrate scope, high enantioselectivity, ease of scale-up, mild reaction conditions, and versatile transformations.

Metal-to-Ligand Ratio-Dependent Chemodivergent Asymmetric Synthesis

Chemodivergent asymmetric synthesis was achieved by tuning the metal-to-ligand ratio in an organometallic catalytic system. Using N-(aroyloxy)phthalimide as the precursor of either an oxygen-centered aroyloxy radical or a nitrogen-centered phthalimidyl radical, enantioselective oxocyanation or aminocyanation of alkenes was achieved separately through a dual photoredox and copper catalysis. The metal-to-ligand ratio can exert chemoselective control while retaining the high enantiopurity of divergent products. Both reactions proceed efficiently with catalyst loading as low as 0.2 mol % and can be performed on a gram scale without loss of chemoselectivity or enantioselectivity. Chemodivergent asymmetric 1,5-aminocyanation or 1,5-oxocyanation of vinylcyclopropane can also be realized by this protocol. Mechanistic investigations involving electron paramagnetic resonance (EPR) experiments were performed to shed light on the stereochemical and chemodivergent results.

Palladium-Catalyzed Carbonylative Four-Component Synthesis of β-Perfluoroalkyl Amides

Transition-metal-catalyzed multicomponent carbonylation is one of the most efficient strategies to construct carbonyl-containing compounds. Herein, a palladium-catalyzed four-component perfluoroalkylation/aminocarbonylation of unactivated alkenes with perfluoroalkyl halides, and amines was developed. A wide range of substrates, including anilines, alkylamines, sulfonamides, and hydrazines are all suitable reaction partners for this catalyst system, resulting in various β-perfluoroalkyl amides with good functional-group tolerance and excellent chemoselectivity. Furthermore, not only alkyl olefins, but also aliphatic alkynes, and even alkyl allenes can all be employed. Notably, several medical and bioactive related molecules are compatible here as well.

Radical 1,5-Chloropentafluorosulfanylation of Unactivated Vinylcyclopropanes and Transformation into α-SF5 Ketones

The radical 1,5-chloropentafluorosulfanylation of vinyl cyclopropanes (VCPs) initiated by Et₃B/O₂ affords allylic pentafluorosulfanyl/homoallylic chloride products through the ring-strain release of the cyclopropane. The VCP substitution pattern was investigated. The utility of this reaction was illustrated in post-transformation of the C═C bond by ozonolysis, giving access to valuable α-SF₅ carbonyl compounds.

A Mn-catalyzed remote C(sp3)-H bond peroxidation triggered by radical trifluoromethylation of unactivated alkenes

A manganese-catalyzed radical relay strategy for the remote trifluoromethylation-peroxidation of unactivated alkenes is disclosed. The electrophilic CF3 group was added to the C[double bond, length as m-dash]C double bonds to afford remote C-centered radicals upon 1,5-HAT, which could be efficiently trapped by Mnn+1OOBu-t species to deliver 1,6-difunctionalized products selectively under mild conditions. t-BuOOH serves as both the oxidant and the peroxy precursor in this transformation.

Visible Light Induced Cu-Catalyzed Asymmetric C(sp3)-H Alkylation

The asymmetric functionalization of C-H is one of the most attractive strategies in asymmetric synthesis. In the past decades, catalytic enantioselective C(sp³)-H functionalization has been intensively studied and successfully applied in various asymmetric bond formations, whereas asymmetric C(sp³)-H alkylation was not well developed. Photoredox catalysis has recently emerged as an efficient way to synthesize organic compounds under mild conditions. Despite many photoinduced stereoselective reactions that have been achieved, the related enantioselective C(sp³)-C(sp³) coupling is challenging, especially of the photocatalytic asymmetric C(sp³)-H radical alkylation. Here, we report a visible light induced Cu catalyzed asymmetric sp³ C-H alkylation, which is effective for coupling with unbiased primary, secondary, and tertiary alkyl fragments in high enantioselectivities. This reaction would provide a new approach for the synthesis of important molecules such as unnatural α-amino acids and late-stage functionalization of bioactive compounds, and will be useful for modern peptide synthesis and drug discovery.

Electrooxidative dearomatization of biaryls: synthesis of tri- and difluoromethylated spiro[5.5]trienones

Radical spirocyclization via dearomatization has emerged as an attractive strategy for the rapid synthesis of structurally diverse spiro molecules. We report the use of electrochemistry to perform an oxidative dearomatization of biaryls leading to tri- and difluoromethylated spiro[5.5]trienones in a user friendly undivided cell set-up and a constant current mode. The catalyst- and chemical oxidant-free dearomatization procedure features ample scope, and employs electricity as the green and sole oxidant.

Photoinduced 1,2-dicarbofunctionalization of alkenes with organotrifluoroborate nucleophiles via radical/polar crossover

Alkene 1,2-dicarbofunctionalizations are highly sought-after transformations as they enable a rapid increase of molecular complexity in one synthetic step. Traditionally, these conjunctive couplings proceed through the intermediacy of alkylmetal species susceptible to deleterious pathways including β-hydride elimination and protodemetalation. Herein, an intermolecular 1,2-dicarbofunctionalization using alkyl N-(acyloxy)phthalimide redox-active esters as radical progenitors and organotrifluoroborates as carbon-centered nucleophiles is reported. This redox-neutral, multicomponent reaction is postulated to proceed through photochemical radical/polar crossover to afford a key carbocation species that undergoes subsequent trapping with organoboron nucleophiles to accomplish the carboallylation, carboalkenylation, carboalkynylation, and carboarylation of alkenes with regio- and chemoselective control. The mechanistic intricacies of this difunctionalization were elucidated through Stern-Volmer quenching studies, photochemical quantum yield measurements, and trapping experiments of radical and ionic intermediates.

Nickel-catalysed migratory hydroalkynylation and enantioselective hydroalkynylation of olefins with bromoalkynes

α-Chiral alkyne is a key structural element of many bioactive compounds, chemical probes, and functional materials, and is a valuable synthon in organic synthesis. Here we report a NiH-catalysed reductive migratory hydroalkynylation of olefins with bromoalkynes that delivers the corresponding benzylic alkynylation products in high yields with excellent regioselectivities. Catalytic enantioselective hydroalkynylation of styrenes has also been realized using a simple chiral PyrOx ligand. The obtained enantioenriched benzylic alkynes are versatile synthetic intermediates and can be readily transformed into synthetically useful chiral synthons.