Reversal of the apparent regiospecificity of NAD(P)H-dependent hydride transfer: the properties of the difluoromethylene group, a carbonyl mimic

Synthesis of gem-Difluorohomoallyl Amines via a Transition-Metal-Free Defluorinative Alkylation of Benzyl Amines with Trifluoromethyl Alkenes

A mild and transition-metal-free defluorinative alkylation of benzyl amines with trifluoromethyl alkenes is reported. The features of this protocol are easy-to-obtain starting materials, a wide range of substrates, and functional group tolerance as well as high atom economy, thus offering a strategy to access a variety of gem-difluorohomoallyl amines, which are extensively distributed in pharmaceuticals and bioactive agents, with excellent chemoselectivity. The primary products can be further transformed to a diversity of 2-fluorinated pyrroline compounds.

Photoinduced radical tandem annulation of 1,7-diynes: an approach for divergent assembly of functionalized quinolin-2(1H)-ones

The first photocatalytic trichloromethyl radical-triggered annulative reactions of amide-linked 1,7-diynes with polyhalomethanes were established for the flexible assembly of functionalized quinolin-2(1H)-ones with generally acceptable yields. With the installation of the aryl group (R1) into the alkynyl moiety, C-center radical-initiated Kharasch-type addition/nucleophilic substitution/elimination cascade to produce quinolin-2(1H)-ones-incorporating gem-dihaloalkene, whereas three examples of polyhalogenated quinolin-2(1H)-ones were afforded when amide-linked 1,7-diynes bearing two terminal alkyne units were subjected to BrCX3 by exploiting dry acetonitrile as a solvent.

Directing-Group-Assisted Non-Strained Ether C-O Bond Homolysis Mediated by Low-Valent Titanium

Ether C-O bonds are typical constituents of organic molecules that are seldom regarded as reactive functional groups except when highly strained. With the assistance of appropriate directing groups, low-valent titanium was found to homolytically cleave non-strained C-O bonds. In particular, a newly designed catechol monoether directing group rendered a route toward the activation of non-benzylic C(sp3)-O bonds. This method has been applied to conventional radical addition reactions to alkenes.

Organo-Photoredox Catalyzed gem-Difluoroallylation of Glycine and Glycine Residue in Peptides

An organo-photoredox catalyzed gem-difluoroallylation of glycine with α-trifluoromethyl alkenes via direct C(sp3)-H functionalization of glycine and C-F bond activation of α-trifluoromethyl alkenes has been described. As a consequence, a broad range of gem-difluoroalkene-containing unnatural amino acids are afforded in moderate to excellent yields. This reaction exhibits multiple merits such as readily available starting materials, broad substrate scope, and mild reaction conditions. The feasibility of this reaction has been highlighted by the late-stage modification of several peptides as well as the improved in vitro antifungal activity of compound 3v toward Valsa mali compared to that with commercial azoxystrobin.

Photoinduced Triphenylphosphine and Iodide Salt Promoted Reductive Decarboxylative Coupling

The transient electron donor-acceptor (EDA) complex has been an emerging area in the photoinduced organic synthesis field, generating radicals without exogenous transition-metal or organic dye-based photoredox catalysts. The catalytic platform to form suitable photoactive EDA complexes for photochemical reduction reactions remains underdeveloped. Herein, a general photoinduced reductive alkylation via the EDA complex strategy is described. A simple yet multifunctional system, triphenylphosphine and iodide salt, promotes the photoinduced decarboxylative hydroalkylation, and reductive defluorinative decarboxylative alkylation of trifluoromethyl alkenes, to access trifluoromethyl alkanes and gem-difluoroalkenes. Moreover, decarboxylative hydroalkylation can be applied to more kinds of electron-deficient alkenes as a general Giese addition reaction.

Synthesis, Reactivity, and Antibacterial Activity of gem-Difluoroalkene, Difluoromethyl, and Trifluoromethyl β-Lactams

New gem-difluoroalkenes were synthesized by the dehydrofluorination of the corresponding 4-CF3-β-lactams. An unexpected rearrangement mechanism of the ester moiety dependent on a stabilizing negative charge was observed. Hydrogenation to 4-CHF2-β-lactams was successful from gem-difluoro-β-lactams.

Photoredox Enabled Defluorinative Benzylation of Trifluoromethyl Alkenes with Alkylarenes

Herein, we report a photoredox enabled defluorinative benzylation of trifluoromethyl alkenes with readily available alkylarenes, which provides convenient access to a series of structurally valuable benzylated gem-difluoroalkenes under mild reaction conditions. The synthetic value of this protocol has been demonstrated by the transformations of several substrates bearing drug moieties, gram-scale reactions, and various further derivatizations of the gem-difluoroalkene products. The preliminary mechanistic investigations suggest a reaction pathway with rate-determining benzyl C-H bond cleavage of toluene followed by benzylic radical formation.

Copper-Catalyzed Protoarylation of gem-Difluoroallenes

A copper-catalyzed protoarylation of gem-difluoroallenes with aryl boronic esters has been developed, enabling highly regioselective synthesis of gem-difluoroalkenes in high yields. The mild reaction conditions allow for a variety of functional groups to be tolerated, and the reaction can be extended to protoalkenylation of gem-difluoroallenes. The synthetic utility of this method has been demonstrated in gram-scale operation as well as synthesis of chiral gem-difluoroalkenes bearing γ-carbon stereogenic centers in moderate enantioselectivity using a chiral bidentate phosphine ligand with a copper catalyst.

Solvent-Controllable C-F Bond Activation for Masked Formylation of α-Trifluoromethyl Alkenes via Organo-Photoredox Catalysis

A solvent-controllable organo-photoredox-catalyzed C-F bond activation for masked formylation of α-trifluoromethyl alkenes with low-priced 1,3-dioxolane as masked formyl radical equivalent has been described. Consequently, a diversity of masked formylated gem-difluoroalkenes and monofluoroalkenes are constructed in moderate to high yields. This approach merits readily available starting materials, mild reaction conditions, and broad substrate scope. The feasibility of this approach has been highlighted by the one-pot masked formylation/hydrolysis sequence to form γ,γ-difluoroallylic aldehydes and late-stage modification of pharmaceutical and natural product derivatives.

O-H bond activation of β,γ-unsaturated oximes via hydrogen atom transfer (HAT) and photoredox dual catalysis

Hydrogen atom transfer (HAT) and photoredox dual catalysis provides a unique opportunity in organic synthesis, enabling the direct activation of C/Si/S-H bonds. However, the activation of O-H bonds of β,γ-unsaturated oximes poses a challenge due to their relatively high redox potential, which exceeds the oxidizing capacity of most currently developed photocatalysts. We here demonstrate that the combination of HAT and photoredox catalysis allows the activation of O-H bond of β,γ-unsaturated oximes. The strategy effectively addresses the oxime's high redox potential and offers a universal pathway for iminoxyl radical formation. Leveraging the versatility of this approach, a diverse array of valuable heterocycles have been synthesized with the use of different radical acceptors. Mechanistic studies confirm a HAT process for the O-H bond activation.

Handling fluorinated gases as solid reagents using metal-organic frameworks

Fluorine is an increasingly common substituent in pharmaceuticals and agrochemicals because it improves the bioavailability and metabolic stability of organic molecules. Fluorinated gases represent intuitive building blocks for the late-stage installation of fluorinated groups, but they are generally overlooked because they require the use of specialized equipment. We report a general strategy for handling fluorinated gases as benchtop-stable solid reagents using metal-organic frameworks (MOFs). Gas-MOF reagents are prepared on gram-scale and used to facilitate fluorovinylation and fluoroalkylation reactions. Encapsulation of gas-MOF reagents within wax enables stable storage on the benchtop and controlled release into solution upon sonication, which represents a safer alternative to handling the gas directly. Furthermore, our approach enables high-throughput reaction development with these gases.

Photo/Ni dual-catalyzed radical defluorinative sulfonylation to synthesize gem-difluoro allylsulfones

Radical defluorinative functionalization of α-trifluoromethyl styrenes represents an effective way toward gem-difluoroalkenes. There are general interests in developing novel synthetic protocols for defluorinative functionalization with various types of radicals. However, reports on the preparation of gem-difluoro allylsulfones via an S-centered radical pathway are limited. Herein, we developed a photo/nickel dual-catalyzed defluorinative sulfonylation that rapidly and reliably synthesizes gem-difluoro allylsulfones. The merit of this protocol is exhibited by its mild conditions and wide scope, thus providing a novel strategy for the sulfonyl radical participating in radical defluorinative coupling.

Deaminative defluoroalkylation of α-trifluoromethylalkenes enabled by photoredox catalysis

Herein, we disclose a new photoredox-catalysed strategy to access gem-difluoroallylarenes from α-trifluoromethylalkenes with sterically hindered primary amines via C-N and C-F bond activation. This deaminative and defluorinative allylation is generally compatible with diverse functional groups and sterically hindered α-3° and 2° primary amines.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Gem-Difluoroallylation of Aryl Sulfonium Salts

The unprecedented photochemical late-stage defluorinative gem-difluoroallylation of aryl sulfonium salts, which are formed site-selectively by direct C(sp²)─H functionalization, is herein disclosed. This method is distinguished by its mild reaction conditions, wide scope, and excellent site-selectivity. As showcase examples, a Flurbiprofen and Pyriproxyfen derivatives could be late stage C(sp²)─H gem-difluoroallylated with high yields. Experimental and computational investigations were conducted.

Diverse reactivity of the gem-difluorovinyl iodonium salt for direct incorporation of the difluoroethylene group into N- and O-nucleophiles

The synthesis of gem-difluoroethylene compounds remains a difficult task in organic synthesis. Here, the direct difluoroethylation reactions of N- and O-nucleophiles including amides and acids were realized with a hypervalent iodine reagent: gem-difluorovinyl iodonium salt (DFVI). The reactions were accomplished via a neighbouring group rearrangement. The gem-difluorovinyl iodonium salt was found to display diverse reactivity due to its unique electronic effect and was applied to the incorporation of difluoroethylene group, including difluorovinylation of carboxylic acids, difluorovinylation and 1,3-cyclic fluorovinylation of amides and 1,1-cyclic difluoroethylation of amines.

Cu-Catalyzed Switchable Asymmetric Defluoroalkylation and [3 + 2] Cycloaddition of Trifluoropropene

Chiral fluorinated amino esters and pyrrolidines are privileged scaffolds in synthetic chemistry and exhibit unique biological properties. We report the facile preparation of these compounds through copper-catalyzed switchable defluoroalkylation and [3 + 2] cycloaddition of trifluoropropene in an asymmetric fashion. The choice of solvent and chiral ligand was crucial for the efficient transformation and exquisite chemoselectivity pattern from identical starting materials that rapidly and reliably incorporate gem-difluoroalkene and trifluoromethyl (CF₃) motifs to generate a diverse range of enantioenriched fluorinated building blocks in good to excellent yields with high asymmetric induction.

CF2Br2 as a Source for Difluoroolefination of 1,3-Enynes via N-Heterocyclic Carbene Catalysis

Commercially available CF₂Br₂ has been used as a convenient source for the rapid and reliable incorporation of the gem-difluorovinyl motif into an allene framework via an N-heterocyclic carbene catalyzed difluoroolefination of 1,3-enynes. The reaction proceeds through a cascade three-component radical relay/elimination process. This protocol is distinguished by its mild conditions, readily accessible starting materials, wide substrate scope, and ease of late-stage functionalization, thus unlocking an untraditional strategy to construct a new class of functionalized gem-difluorovinyl allenes.

On-DNA Hydroalkylation to Introduce Diverse Bicyclo[1.1.1]pentanes and Abundant Alkyls via Halogen Atom Transfer

DNA-encoded libraries have proven their tremendous value in the identification of new lead compounds for drug discovery. To access libraries in new chemical space, many methods have emerged to transpose traditional mol-scale reactivity to nmol-scale, on-DNA chemistry. However, procedures to access libraries with a greater fraction of C(sp3) content are still limited, and the need to "escape from flatland" more readily on-DNA remains. Herein, we report a Giese addition to install highly functionalized bicyclo[1.1.1]pentanes (BCPs) using tricyclo[1.1.1.01,3]pentane (TCP) as a radical linchpin, as well as other diverse alkyl groups, on-DNA from the corresponding organohalides as non-stabilized radical precursors. Telescoped procedures allow extension of the substrate pool by at least an order of magnitude to ubiquitous alcohols and carboxylic acids, allowing us to "upcycle" these abundant feedstocks to afford non-traditional libraries with different physicochemical properties for the small-molecule products (i.e., non-peptide libraries with acids). This approach is amenable to library production, as a DNA damage assessment revealed good PCR amplifiability and only 6% mutated sequences for a full-length DNA tag.

Photocatalyzed Defluorinative Dichloromethylation of α-CF3 Alkenes Using CHCl3 as the Radical Source

A visible-light-induced defluorinative dichloromethylation of α-CF₃ alkenes was developed with cheap and readily accessible chloroform simultaneously as a dichloromethylation reagent and reaction medium, leading to the facile preparation of new polyhalogenated scaffolds. Notably, the change from CHCl₃ to CDCl₃ offers a straightforward pathway for accessing the deuterated analogues with excellent degrees of D incorporation. Mechanistic studies suggested the reaction underwent a radical addition of the dichloromethyl radical with alkenes, followed by sequential single-electron transfer and defluorination. This protocol features mild conditions, easy operation, facile scalability, and high efficiency, allowing convenient access to dichloronated gem-difluoroalkenes.

Photoredox Metal-Free Allylic Defluorinative Silylation of α-Trifluoromethylstyrenes with Hydrosilanes

We report an efficient strategy that combines organic photoredox and hydrogen atom transfer to deliver gem-difluoroallylsilanes via defluorinative silylation of α-trifluoromethylstyrenes using hydrosilanes as silicon sources. This protocol provides an environmentally friendly approach for the preparation of structurally diverse gem-difluoroallylsilanes with excellent functional group compatibility and renders it suitable for late-stage modification of bioactive and complex molecules.

Oxalates as Activating Groups for Tertiary Alcohols in Photoredox-Catalyzed gem-Difluoroallylation To Construct All-Carbon Quaternary Centers

Construction of challenging and important all-carbon quaternary centers has received growing attention. Herein, with oxalates as activating groups for tertiary alcohols, we report photoredox-catalyzed gem-difluoroallylation to construct all-carbon quaternary centers enabled by efficient tertiary radical addition to α-trifluoromethyl alkenes. This transformation shows good functional group tolerance for both α-trifluoromethyl alkenes and oxalates. Moreover, this strategy is also successfully applied to the synthesis of monofluoralkenes from the corresponding electron-rich gem-difluoroalkenes and cesium tertiary alkyl oxalates under modified conditions.

Nickel-Catalyzed Cross-Electrophile Coupling Reactions between Allylic Acetates and gem-Difluorovinyl Tosylate

A nickel-catalyzed cross-electrophile coupling of allylic acetates and gem-difluorovinyl tosylate is presented, which first achieves allylic gem-difluoroolefins via C(sp³)-C(sp²) cross-electrophile coupling. In addition, this protocol was performed under mild reaction conditions, affording a variety of allylic gem-difluorovinyl arenes in moderate to good yields. Moreover, both linear and branched allylic acetate could produce a linear cross-coupling product exclusively. Mechanistic studies reveal that the reaction involves two different Ni(0)/Ni(II) catalytic cycles.

Nickel-Catalyzed Defluorinative Coupling of Aliphatic Aldehydes with Trifluoromethyl Alkenes

A simple procedure is reported for the nickel-catalyzed defluorinative alkylation of unactivated aliphatic aldehydes. The process involves the catalytic reductive union of trifluoromethyl alkenes with aldehydes using a nickel complex of a 6,6'-disubstituted bipyridine ligand with zinc metal as the terminal reductant. The protocol is distinguished by its broad substrate scope, mild conditions, and simple catalytic setup. Reaction outcomes are consistent with the intermediacy of an α-silyloxy(alkyl)nickel intermediate generated by a low-valent nickel catalyst, silyl electrophile, and the aldehyde substrate. Mechanistic findings with cyclopropanecarboxaldehyde provide insights into nature of the reactive intermediates and illustrate fundamental reactivity differences that are governed by subtle changes in ligand and substrate structure.

Photoredox-Catalyzed Allylic Defluorinative Alkoxycarbonylation of Trifluoromethyl Alkenes through Intermolecular Alkoxycarbonyl Radical Addition

The gem-difluoroalkene moiety is an ideal carbonyl bioisostere in medicinal chemistry, but efficient synthesis of β-gem-difluoroalkene esters remains challenging so far. Herein, we disclose a photoredox-catalyzed allylic defluorinative alkoxycarbonylation of trifluoromethyl alkenes enabled by intermolecular alkoxycarbonyl radical addition. A wide variety of alcohol oxalate derivatives were amenable, affording various β-gem-difluoroalkene esters with excellent functional group tolerance. Notably, the potential synthetic value of this method is highlighted by successful late-stage modification for bioactive molecules.

Access to gem-Difluoroalkenes via Organic Photoredox-Catalyzed gem-Difluoroallylation of Alkyl Iodides

An organic photoredox-catalyzed gem-difluoroallylation of α-trifluoromethyl alkenes with alkyl iodides via C-F bond cleavage for the synthesis of gem-difluoroalkene derivatives is reported. This transition-metal-free transformation utilized a readily available organic dye 4CzIPN as the sole photocatalyst and employed a common chemical N,N,N',N'-tetramethylethylenediamine as the radical activator of alkyl iodides via halogen-atom transfer. In addition, a variety of iodides, including primary, secondary, and tertiary alkyl iodides, were tolerated and provided good to high yields.

Ligand-free copper-catalyzed borylative defluorination: access to gem-difluoroallyl boronic acid derivatives

We report a ligand-free copper-catalyzed β-borylation, defluorination of β-substituted, α-trifluoromethyl-α,β-unsaturated esters. The reaction affords geminal-difluoroallyl boronic acid derivatives in moderate to good yield. The reaction was tolerant of various substrates, and the utility of products was demonstrated in the defluorinative functionalization of the difluoroalkene to afford enol ethers.

gem-Difluorovinylation of alkynyl bromoarenes via dual nickel-/palladium-catalyzed cross-electrophile coupling

A dual nickel-/palladium-catalyzed gem-difluorovinylation of alkynyl bromoarenes is presented. This method proceeds smoothly to afford various dihydrobenzofuran compounds containing gem-difluorovinyl fragments with excellent stereoselectivities.

Visible-light-induced transition-metal-free defluorosilylation of α-trifluoromethylalkenes via hydrogen atom transfer of silanes

A green and feasible synthetic protocol for silyl gem-difluoroalkenes was developed using α-trifluoromethylalkenes and silanes via the synergistic combination of photoredox and hydrogen-atom transfer catalysis under visible light irradiation.

Electrochemical synthesis of functionalized gem-difluoroalkenes with diverse alkyl sources via a defluorinative alkylation process

An electrochemical defluorinative alkylation of α-trifluoromethyl alkenes is described. This reaction enables the preparation of functionalized gem-difluoroalkenes with diverse alkyl sources including organohalides, NHP esters, and Katritzky salts.

Glycosyl-Radical-Based Synthesis of C-Alkyl Glycosides via Photomediated Defluorinative gem-Difluoroallylation

We have developed a stereoselective, glycosyl radical-based method for the synthesis of C-alkyl glycosides via a photomediated defluorinative gem-difluoroallylation reaction. We demonstrate for the first time that glycosyl radicals, generated from glycosyl bromides, can readily participate in a photomediated radical polar crossover process, affording a diverse array of gem-difluoroalkene containing C-glycosides. Notable features of this method include scalability, mild conditions, broad substrate scope, and suitability for the late-stage modification of complex molecules.

Sc(OTf)3-Catalyzed C2-Selective Cyanation/Defluorination Cascade of Perfluoroalkylated 3-Indolylmethanols and Application to the Synthesis of 3-Fluoro(perfluoroalkyl)-β-carbolines

An unprecedented Sc(OTf)₃-catalyzed C2-selective cyanation/defluorination cascade of perfluoroalkylated 3-indolylmethanols with TMSCN is described, which provides a novel and practical strategy for the synthesis of structurally diverse 3-(2-cyano)-indolyl substituted gem-difluoroalkenes and β-fluoro-β-perfluoroalkylalkenes. The reaction features excellent regio- and stereoselectivity and broad substrate scope. Notably, the obtained gem-difluoroalkenes and β-fluoro-β-perfluoroalkylalkenes could be easily transformed into 3-fluoro(perfluoroalkyl)-β-carbolines with excellent efficiency simply by treating them with Grignard reagents or DIBAL-H under mild reaction conditions.

Photoredox relay-catalyzed gem-difluoroallylation of alkyl iodides

Herein, a new example of relay catalysis, using a combination of Mn₂(CO)₁₀ and an iridium-based photocatalyst, is reported. In our relay catalytic reaction, the Mn catalyst and iridium-based photocatalyst catalyze the reaction at different stages in the desired sequence under the same reaction conditions, and do not inhibit each other. This convenient method transforms a broad scope of alkyl iodides into the corresponding gem-difluoroalkenes via C(sp³)-C(sp³) bond construction. The protocol has good functional group tolerance and is suitable for the late-stage modification of multifunctional complex molecules.

Photoredox-mediated hydroalkylation and hydroarylation of functionalized olefins for DNA-encoded library synthesis

DNA-encoded library (DEL) technology features a time- and cost-effective interrogation format for the discovery of therapeutic candidates in the pharmaceutical industry. To develop DEL platforms, the implementation of water-compatible transformations that facilitate the incorporation of multifunctional building blocks (BBs) with high C(sp3) carbon counts is integral for success. In this report, a decarboxylative-based hydroalkylation of DNA-conjugated trifluoromethyl-substituted alkenes enabled by single-electron transfer (SET) and subsequent hydrogen atom termination through electron donor-acceptor (EDA) complex activation is detailed. In a further photoredox-catalyzed hydroarylation protocol, the coupling of functionalized, electronically unbiased olefins is achieved under air and within minutes of blue light irradiation through the intermediacy of reactive (hetero)aryl radical species with full retention of the DNA tag integrity. Notably, these processes operate under mild reaction conditions, furnishing complex structural scaffolds with a high density of pendant functional groups.

Fluoride-Triggered Synthesis of 1-Aryl-2,2-difluoroalkenes via Desilylative Defluorination of (1-Aryl)-2,2,2-trifluoroethyl-silanes

An efficient route for the synthesis of 1-aryl-2,2-difluoroalkenes via 1,2-desilylative defluorination is disclosed. Only a catalytic amount of fluoride source is required to initiate the desilylation and afford gem-difluoroalkenes in very good to quantitative yields, using mild reaction conditions in dimethyl carbonate as a green solvent. This reaction uses (1-aryl)-2,2,2-trifluoroethyl-silanes, which are easily prepared via the insertion reaction of trifluoroethyl diazo alkanes into the Si-H bond of tertiary organosilanes. (1-Aryl)-perfluoroalkyl-silanes cleanly afford the corresponding (Z)-1-benzylideneperfluoroalkanes, which upon hydrodefluorination furnish the (E)-β(perfluoroalkyl)styrene derivatives with excellent yield and complete stereoselectivity. A one-pot system involving sequential insertion and desilylative-defluorination is also suitable for this transformation. This method demonstrates the usefulness of organosilanes toward the preparation of fluorinated alkenes as synthetically useful targets.

Ni-Catalyzed Ligand-Controlled Regiodivergent Reductive Dicarbofunctionalization of Alkenes

Transition-metal-catalyzed dicarbofunctionalization of alkenes involving intramolecular Heck cyclization followed by intermolecular cross-coupling has emerged as a powerful engine for building heterocycles with sterically congested quaternary carbon centers. However, only exo-cyclization/cross-coupling products can be obtained; endo-selective cyclization/cross-coupling has not been reported yet and still poses a formidable challenge. We herein report the first example of catalyst-controlled dicarbofunctionalization of alkenes for the regiodivergent synthesis of five- and six-membered benzo-fused lactams bearing all-carbon quaternary centers. Using a chiral Pyrox- or Phox-type bidentate ligand, 5-exo cyclization/cross-couplings proceed favorably to produce indole-2-ones in good yields with excellent regioselectivity and enantioselectivities (up to 98% ee). When C6-carboxylic acid-modified 2,2'-bipyridine was used as the ligand, 3,4-dihydroquinolin-2-ones were obtained in good yields through 6-endo-selective cyclization/cross-coupling processes. This transformation is modular and tolerant of a variety of functional groups. The ligand rather than the substrate structures precisely dictates the regioselectivity pattern. Moreover, the synthetic value of this regiodivergent protocol was demonstrated by the preparation of biologically relevant molecules and structural scaffolds.

Mechanistic insights into Ni-catalyzed hydrogen atom transfer (HAT)-triggered hydrodefluorination of CF3-substituted alkenes

We report the first computational study on a nickel hydride HAT-initiated catalytic reaction, a novel hydrodefluorination of CF3-substituted aryl alkenes to afford gem-difluoroalkenes. This study provides detailed mechanistic insights into the reaction, including HAT from NiH to C[double bond, length as m-dash]C, a carbon radical rebound to nickel to facilitate chemoselective defluorination, and a two-state reactivity of Ni(ii) enabling σ-bond metathesis with PhSiH3 to regenerate the catalyst. The findings can have implications for developing new metal hydride HAT-initiated reactions.

Chemoselective catalytic hydrodefluorination of trifluoromethylalkenes towards mono-/gem-di-fluoroalkenes under metal-free conditions

Fluorine-containing moieties show significant effects in improving the properties of functional molecules. Consequently, efficient methods for installing them into target compounds are in great demand, especially those enabled by metal-free catalysis. Here we show a diazaphospholene-catalyzed hydrodefluorination of trifluoromethylalkenes to chemoselectively construct gem-difluoroalkenes and terminal monofluoroalkenes by simple adjustment of the reactant stoichiometry. This metal-free hydrodefluorination features mild reaction conditions, good group compatibility, and almost quantitative yields for both product types. Stoichiometric experiments indicated a stepwise mechanism: hydridic addition to fluoroalkenes and subsequent β-F elimination from hydrophosphination intermediates. Density functional theory calculations disclosed the origin of chemoselectivity, regioselectivity and stereoselectivity, suggesting an electron-donating effect of the alkene-terminal fluorine atom.