Photoredox/Hydrogen Atom Transfer Cocatalyzed C–H Difluoroallylation of Amides, Ethers, and Alkyl Aldehydes

Visible-Light-Mediated Radical α-C(sp3)─H gem-Difluoroallylation of Amides with Trifluoromethyl Alkenes via Halogen Atom Transfer and 1,5-Hydrogen Atom Transfer

Direct gem-difluoroallylation at the α-carbonyl position is a challenging process by conventional methods. Herein we report the photocatalytic radical α-C(sp3)─H gem-difluoroallylation of amides with trifluoromethyl alkenes to access the target compounds with good yields and functional group tolerance. The mild and effective conditions allow gem-difluoroalkene motifs as carbonyl bioisosteres incorporated concisely to some complex molecules, including gemfibrozil and estrone derivatives, presenting great potential for late-stage functionalization of drugs, natural products, and bioactive intermediates. Mechanistic investigations suggest a radical pathway combining XAT and 1,5-HAT.

Visible Light Photoredox-Catalyzed Radical Defluorinative Arylation of α-Trifluoromethyl Alkenes with Aryl Chlorides

Photocatalytic defluorinative cross-coupling reactions of α-trifluoromethyl alkenes with diverse radical precursors have emerged as a powerful strategy for the synthesis of gem-difluoroalkenes. However, the radical defluorinative arylation is relatively rare due to the limitation of aryl radical precursors. Aryl chlorides, as ideal candidates, remain a large challenge in this reaction because of the chemical inertness of the C(sp2)-Cl bond and their high negative reduction potential. Herein, we report a radical defluorinative arylation of α-trifluoromethyl alkenes with aryl chlorides as aryl radical precursors through a consecutive photoinduced electron transfer (ConPET) process. This protocol features mild conditions, operational simplicity, wide substrate scope, and functional group tolerance, producing a diverse range of benzylic gem-difluoroalkenes in moderate to good yields. The scale-up reaction and the valuable transformations of products demonstrate the great potential applications of this approach.

Visible-Light-Induced Synergistic W/Cr Catalyzed gem-Difluoroallylation of Unactivated Alkanes

Currently, the scope of the Nozaki-Hiyama-Kishi (NHK) reaction is limited to aldehydes and ketones to construct alcohol derivatives. Herein, we have described a visible-light-induced synergistic W/Cr(III)-catalyzed NHK-type gem-difluoroallylation reaction of unactivated cyclic and linear alkanes. The reaction merits feedstock materials, mild reaction conditions, and a wide functionality tolerance. Mechanistic studies imply the favorable reduction of CrCl3 to CrCl2 by reduced decatungstate W10O325-, thus closing the catalytic cycle.

Photocatalytic Three-Component Reductive Coupling Synthesis of gem-Difluorohomoallyl Secondary Amines

gem-Difluorohomoallyl amines, an important class of gem-difluoroalkenes, are prevalent moieties in many bioactive compounds. However, limited methods are suitable for the synthesis of this type of compound containing secondary amines. Here, we display a photocatalytic multicomponent protocol for the synthesis of gem-difluoroalkenes containing secondary amines, which makes use of readily available materials: arylamines, alkyl aldehydes, and α-trifluoromethyl alkenes. Moreover, ketones and secondary amines are also suitable substrates. Preliminary mechanistic experiments indicate that a key α-amino radical was involved, generated from the reduction of in situ-formed imines (or iminium ions) by a reduced photocatalyst. Subsequent addition of the α-amino radical to α-trifluoromethyl alkenes and β-F elimination deliver the desired products.

Decatungstate-Photocatalyzed Transformations of 2-Bromo-3,3,3-trifluoropropene for Selective Synthesis of Z/E-β-CF3-Enones

Condition-controlled switchable and divergent transformations of cost-effective 2-bromo-3,3,3-trifluoropropene (BTP) and aldehydes were realized using a decatungstate (TBADT)-photocatalyzed strategy. The hydroacylated products, i.e., β,β-Br,CF3-ketones, can be applied as highly functionalized synthetic building blocks for the selective synthesis of (Z/E)-β-CF3-enones. Utilizing this methodology, a broad range of commercially available aromatic and aliphatic aldehydes as well as numerous complex aldehydes, such as lily aldehyde, cyclamen aldehyde, citronellal, vanillin, and aldehydes containing bioactive moieties, including ibuprofen, gemfibrozil, naproxen, flurbiprofen, oleic acid, and aspirin, may be proficiently employed in this transformative process.

Chemodivergent alkylation of trifluoromethyl alkenes via photocatalytic coupling with alkanes

gem-Difluoroalkenes and trifluoromethyl alkanes are prominent structures in biologically active compounds. Radical alkylation of α-trifluoromethyl alkenes represents a useful strategy to access these structures. However, reported methods have relied on the use of pre-functionalized radical precursors and examples involving the use of simple hydrocarbons as coupling partners are elusive. Here we report a chemodivergent methodology based on the direct activation of C(sp3)-H bonds enabled by HAT photoredox catalysis. This protocol provides an efficient platform for preparing both gem-difluoroalkenes and trifluoromethyl alkanes from ubiquitous hydrocarbon feedstocks, including gaseous alkanes. Importantly, chemoselectivity is easily achieved by simple modification of reaction conditions and/or additives.

Dicarbofunctionalization of Vinylarenes with Pyridine and Aldehydes via Photocatalytic Hydrogen Atom Transfer

We describe a metal-free and mild three-component reaction utilizing vinylarenes, alkyl aldehydes, and 4-cyanopyridine. In this reaction, the scope of vinylarenes and alkyl aldehydes includes over 40 examples, generating a variety of β-pyridinyl ketones. Moreover, potential applications of this method have been demonstrated by the functionalization of pharmaceutical molecules. An acyl radical is proposed to be produced via a polarity-matched hydrogen atom transfer between alkyl aldehydes and a triplet-state diradical from benzophenone.

Assembly of functionalized gem-difluoroalkenes via photocatalytic defluorocyanoalkylation and defluoroacylation of α-CF3 styrenes with oxime esters

We report an efficient photocatalytic protocol for the defluorocyanoalkylation and defluoroacylation of α-trifluoromethyl styrenes by utilizing oxime esters as radical donors, allowing for the preparation of diverse gem-difluoroalkenes. The treatment of α-trifluoromethyl styrenes with cyclobutanone oxime esters led to the formation of distal cyano group-anchored gem-difluoroalkenes. Notably, adding K2CO3 as an inorganic base to the photocatalytic system afforded γ,γ-difluoroallylic ketones by utilizing acyl oxime esters as the acylating agents. Preliminary mechanistic investigations into this reaction pathway revealed the involvement of single-electron reduction, C-C bond cleavage initiated by iminyl radicals, radical addition, and β-fluoride elimination steps.

Spirobipyridine Ligand Enabled Iridium-Catalyzed Site-Selective C-H Activation via Non-Covalent Interactions

The selective borylation of specific C-H bonds in organic synthesis remains a formidable challenge. In this study, we present a novel spirobipyridine ligand that features a binaphthyl backbone. This ligand facilitates the iridium-catalyzed selective C-H borylation of benzene derivatives. The ligand is designed with "side-arm-wall" substituents that allow vicinal di- or multi-substituted benzene derivatives to approach metal center and effectively block other reactive sites by non-covalent interactions with substrates. The effectiveness of this strategy is demonstrated by the successful selective distal C-H activation of various alkaloids and its broad compatibility with functional groups.

Photoredox/HAT-Catalyzed Intramolecular Hydrocyclization of Alkenes toward 2,3-Fused Quinazolinones and Dihydroquinazolinones

New photochemical approaches to 2,3-fused quinazolinones and dihydroquinazolinones are disclosed. The intramolecular hydrocyclization proceeds in moderate to excellent yields across diverse alkenes with high regioselectivity and diastereocontrol. Mechanistic studies indicated that the radical cascade processes involve thiophenol acting as single-electron transfer and hydrogen atom transfer reagents. The success of the gram-scale synthesis proves the strategy can be used for practical applications.

Transition-Metal-Free Late-Stage Decarboxylative gem-Difluoroallylation of Primary Alkyl Acids

A transition-metal-free late-stage decarboxylative gem-difluoroallylation of carboxylic acids with α-trifluoromethyl alkenes has been described by the use of organo-photoredox catalysis. Both primary alkyl and heteroaryl acids were readily incorporated. This approach merits feedstock materials, mild reaction conditions, and wide functionality tolerance. The synthetic utility of this approach has been highlighted by the late-stage functionalization of a variety of acid-containing natural products and drug molecules.

Photocatalytic Defluorinative α-Aminoalkylation of Allylic Difluorides

A photocatalytic process was devised to synthesize monofluoroalkenes via defluorinative functionalization of allylic difluorides. N-Alkylanilines are used as precursors to α-aminoalkyl radicals, which undergo regioselective addition to allylic difluorides, and subsequent SET and fluoride elimination produce monofluoroalkenes. C-C bond formation on the aniline is site-selective for the least substituted carbon α to nitrogen.

Nickel-catalyzed hydrodefluorination/deuterodefluorination of CF3-alkenes with formic acid

The synthesis of deuterated gem-difluoroalkenes via selective deuterodefluorination of β-CF3-cinnamates using a nickel catalyst has been reported for the first time. Commercially available deuterated formic acid is a cheap and convenient deuterium source. The nickel-catalyst showed high selectivity for monodefluorination and avoided competitive reactions such as multiple defluorination or hydrogenation.

Electroreductive Remote Benzylic C(sp3)-H Arylation of Aliphatic Ethers Using Cyanoarenes for the Synthesis of α-(Hetero)aryl Ethers

An iodoarene-driven electroreductive remote C(sp3)-H arylation of unsymmetrical 1-(o-iodoaryl)alkyl ethers with cyanoarenes for the site selective synthesis of α-(hetero)aryl ethers is developed. With the introduction of cyanoarenes as both aryl sources and electron transfer mediators, this method includes an iodoarene-driven strategy to enable the regiocontrollable formation of two new bonds, one C(sp2)-H bond, and one C(sp2)-C(sp3) bond, in a single reaction step through the sequence of halogen atom transfer (XAT), hydrogen atom transfer (HAT), radical-radical coupling, and decyanation.

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.

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.

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.

Selective and controllable amination and defluoroamidation of α-trifluoromethylstyrene

We present a blueprint for the amination and defluoroamidation of α-trifluoromethylstyrene. This practical protocol presents a general method for the diversity-oriented synthesis of vicinal trifluoromethyl amines and gem-difluoro alkenes from α-trifluoromethylstyrene maintaining excellent chemoselectivity. The synthetic strategy features outstanding atom economy and wide functional group tolerance under mild reaction conditions.

Enantioselective catalytic radical decarbonylative azidation and cyanation of aldehydes

Empowered by the ubiquity of carbonyl functional groups in organic compounds, decarbonylative functionalization was prevalent in the construction of complex molecules. Under this context, asymmetric decarbonylative functionalization has emerged as an efficient pathway to accessing chiral motifs. However, ablation of enantiomeric control in a conventional 2e transition metal-catalyzed process was notable because of harsh conditions (high temperatures, etc.) that are usually required. To address this challenge and use readily accessible aldehyde directly, we report the asymmetric radical decarbonylative azidation and cyanation. Diverse aldehydes were directly used as alkyl radical precursor, engaging in the subsequent inner-sphere or outer-sphere ligand transfer where functional motifs (CN and N3) could be incorporated in excellent site- and enantioselectivity. Mild conditions, broad scope, excellent regioselectivity (driven by polarity-matching strategy), and enantioselectivity were shown for both transformations. This radical decarbonylative strategy using aldehydes as alkyl radical precursor has offered a powerful reaction manifold in asymmetric radical transformations to construct functional motifs regio- and stereoselectively.

Recent Advances in C-H Functionalisation through Indirect Hydrogen Atom Transfer

The functionalisation of C-H bonds has been an enormous achievement in synthetic methodology, enabling new retrosynthetic disconnections and affording simple synthetic equivalents for synthons. Hydrogen atom transfer (HAT) is a key method for forming alkyl radicals from C-H substrates. Classic reactions, including the Barton nitrite ester reaction and Hofmann-Löffler-Freytag reaction, among others, provided early examples of HAT. However, recent developments in photoredox catalysis and electrochemistry have made HAT a powerful synthetic tool capable of introducing a wide range of functional groups into C-H bonds. Moreover, greater mechanistic insights into HAT have stimulated the development of increasingly site-selective protocols. Site-selectivity can be achieved through the tuning of electron density at certain C-H bonds using additives, a judicious choice of HAT reagent, and a solvent system. Herein, we describe the latest methods for functionalizing C-H/Si-H/Ge-H bonds using indirect HAT between 2018-2023, as well as a critical discussion of new HAT reagents, mechanistic aspects, substrate scopes, and background contexts of the protocols.

Photoredox radical/polar crossover enables C-H gem-difunctionalization of 1,3-benzodioxoles for the synthesis of monofluorocyclohexenes

A photocatalytic C-H gem-difunctionalization of 1,3-benzodioxoles with two different alkenes for the synthesis of highly functionalized monofluorocyclohexenes is described. Using 4CzIPN as the photocatalyst, the direct single electron oxidation of 1,3-benzodioxoles allows their defluorinative coupling with α-trifluoromethyl alkenes to produce gem-difluoroalkenes in a redox-neutral radical polar crossover manifold. The C-H bond of the resultant γ,γ-difluoroallylated 1,3-benzodioxoles was further functionalized via radical addition to electron-deficient alkenes using a more oxidizing iridium photocatalyst. The capture of in situ generated carbanions by an electrophilic gem-difluoromethylene carbon and consecutive β-fluoride elimination afford monofluorocyclohexenes. The synergistic combination of multiple termination pathways of carbanions enables rapid incorporation of molecular complexity via stitching simple and readily accessible starting materials together.

Defluorinative Transformation of (2,2,2-Trifluoroethyl)arenes Catalyzed by the Phosphazene Base t-Bu-P2

In this study, we demonstrated that 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-Bu-P2) catalyzes the defluorinative functionalization reactions of (2,2,2-trifluoroethyl)arenes with alkanenitriles to produce monofluoroalkene products. The reaction proceeds through HF elimination from a (2,2,2-trifluoroethyl)arene to form a gem-difluorostyrene intermediate, which is followed by nucleophilic addition of an alkanenitrile and elimination of a fluoride anion. The catalysis is compatible with a variety of functional groups.

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.

Organophotoredox and Hydrogen Atom Transfer Cocatalyzed C-H Alkylation of Quinoxalin-2(1H)-ones with Aldehydes, Amides, Alcohols, Ethers, or Cycloalkanes

Described is a mild method that merges organophotoredox catalysis with hydrogen atom transfer to enable C-H alkylation of quinoxalin-2(1H)-ones with feedstock aldehydes, amides, alcohols, ethers, or cycloalkanes. This reaction occurred under environmentally benign and external oxidant-free reaction conditions, providing a general and sustainable access to various C3-alkylated quinoxalinone derivatives with broad substituent diversity and good functional group compatibility.

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.

Visible-Light-Induced C-F and C-N Bond Cleavage for the Synthesis of gem-Difluoroalkenes

Herein, we describe a novel and efficient photoredox catalytic radical addition/defluoroalkylation coupling reaction between primary amines and trifluoromethyl-substituted alkenes. A series of gem-difluoroalkenes were synthesized via C-N bond cleavage of α-3°, α-2°, and α-1° amines under visible light irradiation. This reaction is characterized by a broad substrate scope and good functional group tolerance.

Visible-light-induced defluorinative carbonylative coupling of alkyl iodides with α-trifluoromethyl substituted styrenes

A visible-light-mediated defluorinative carbonylative cross-coupling of alkyl iodides with α-trifluoromethyl styrenes has been developed. The reaction occurs at room temperature under blue light irradiation, and various gem-difluoroalkenes were obtained in moderate to good yields. Synthetic transformations of the obtained product were performed as well.

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.

Defluorinative C-C Bond-Forming Reaction of Trifluoromethyl Alkenes with gem-(Diborylalkyl)lithiums

We report the transition-metal-free defluorinative C-C bond-forming reaction of trifluoromethyl alkenes with gem-(diborylalkyl)lithiums. This synthetic strategy provides access to a variety of 4,4-difluoro homoallylic diboronate esters, which serve as versatile intermediates in the efficient preparation of valuable gem-difluoroalkene derivatives. Further synthetic modifications are conducted to demonstrate the synthetic utility of the obtained 4,4-difluoro homoallylic diboronate esters.

Synthesis of 5-Fluoro-dihydroindolizines from Pyrrole-2-acetic Acids and Trifluoromethyl Alkenes via Dual C-F Bond Cleavage in a CF3 Group

Herein, we describe the synthesis of 5-fluoro-dihydroindolizines via dual C-F bond cleavage in a trifluoromethyl group. The photocatalytic defluorinative coupling of pyrrole-2-acetic acids and α-trifluoromethyl alkenes cleaved the first C-F bond, providing gem-difluoroalkenes bearing an unprotected pyrrole motif. Subsequently, an intramolecular S_NV reaction closed the ring by forming a C-N bond concomitantly with the cleavage of the second C-F bond. Using indole-2-acetic acids as the substrates, the reactions also allow the assembly of 6-fluoro-dihydropyrido[1,2-a]indoles.

Site-Selective C(sp3)–H Functionalizations Mediated by Hydrogen Atom Transfer Reactions via α-Amino/α-Amido Radicals

Amines and amides, as N-containing compounds, are ubiquitous in pharmaceutically-active scaffolds, natural products, agrochemicals, and peptides. Amides in nature bear a key responsibility for imparting three-dimensional structure, such as in proteins. Structural modifications to amines and amides, especially at their positions α to N, bring about profound changes in biological activity oftentimes leading to more desirable pharmacological profiles of small drug molecules. A number of recent developments in synthetic methodology for the functionalizations of amines and amides omit the need of their directing groups or pre-functionalizations, achieving direct activation of the otherwise relatively benign C(sp3)–H bonds α to N. Among these, hydrogen atom transfer (HAT) has proven a very powerful platform for the selective activation of amines and amides to their α-amino and α-amido radicals, which can then be employed to furnish C–C and C–X (X = heteroatom) bonds. The abilities to both form these radicals and control their reactivity in a site-selective manner is of utmost importance for such chemistries to witness applications in late-stage functionalization. Therefore, this review captures contemporary HAT strategies to realize chemo- and regioselective amine and amide α-C(sp3)–H functionalization, based on bond strengths, bond polarities, reversible HAT equilibria, traceless electrostatic-directing auxiliaries, and steric effects of in situ-generated HAT agents.

1 Introduction

2 Functionalizations of Amines

3 Functionalizations of Carbamates

4 Functionalizations of Amides

5 Conclusion

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.

Recent advances in radical enabled selective Csp3-F bond activation of multifluorinated compounds

Fluorine-containing molecules have found broad applications in pharmaceutical and agrochemical industries as introducing fluorine into a molecule could significantly tune the biological activities of parent molecules. Thus, the synthesis of fluorine-containing molecules has received substantial attention over the past few decades. As a complementary strategy for the synthesis of fluorinated compounds through new C_sp³-F bonds formation, selective cleavage of inert C_sp³-F bonds from easily-available and cost-effective multifluorinated molecules, such as fluoroalkylaromatics, α-trifluoromethyl alkenes and α-multifluorinated carbonyl compounds, has been emerging as an attractive alternative to access fluorine-containing molecules. Moreover, the inherent nature of radical reactions offers the opportunity for the selective C_sp³-F functionalizations to occur under mild conditions. In this regard, the development of photoredox catalysis, transition-metal catalysis, or electrochemistry to enable radical species generation via selective C_sp³-F cleavage has gained broad attention and substantial progress has been made over recent years. This highlight summerizes the recent advances in the single-electron-transfer enabled selective functionalizations of C_sp³-F bonds in multifluorinated compounds via radical pathways.

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.

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.

Photochemical and electrochemical strategies in C–F bond activation and functionalization

The recent advances in photochemical or electrochemical C–F bond activation and functionalization have been summarized and discussed.

Copper-catalyzed direct monofluoroalkenylation of C(sp3)–H bonds via decarboxylation of α-fluoroacrylic acids

Herein, a protocol for the copper-catalyzed direct monofluoroalkenylation of C(sp3)–H bonds is reported.

Recent Advances in C-F Bond Cleavage Enabled by Visible Light Photoredox Catalysis

The creation of new bonds via C-F bond cleavage of readily available per- or oligofluorinated compounds has received growing interest. Using such a strategy, a myriad of valuable partially fluorinated products can be prepared, which otherwise are difficult to make by the conventional C-F bond formation methods. Visible light photoredox catalysis has been proven as an important and powerful tool for defluorinative reactions due to its mild, easy to handle, and environmentally benign characteristics. Compared to the classical C-F activation that proceeds via two-electron processes, radicals are the key intermediates using visible light photoredox catalysis, providing new modes for the cleavage of C-F bonds. In this review, a summary of the visible light-promoted C-F bond cleavage since 2018 was presented. The contents were classified by the fluorosubstrates, including polyfluorinated arenes, gem-difluoroalkenes, trifluoromethyl arenes, and trifluoromethyl alkenes. An emphasis is placed on the discussion of the mechanisms and limitations of these reactions. Finally, my personal perspective on the future development of this rapidly emerging field was provided.

Photoredox-Catalyzed Difunctionalization of Unactivated Olefins for Synthesizing Lactam-Substituted gem-Difluoroalkenes

Herein, the synthesis of lactam-substituted gem-difluoroalkenes has been developed through a photoredox-catalyzed radical cascade reaction. This developed photoredox-catalyzed, Brønsted base-assisted intramolecular 5-exo-trig cyclization/intermolecular radical addition/β-fluoride elimination reaction offers a simple method for producing lactam, carbamate, or urea-substituted gem-difluoroalkenes with good functional group tolerance and high yields.

Electroreductive Cross-Coupling of Trifluoromethyl Alkenes and Redox Active Esters for the Synthesis of Gem-Difluoroalkenes

An electroreductive access to gem-difluoroalkenes has been developed through the decarboxylative/defluorinative coupling of N-hydroxyphtalimides esters and α-trifluoromethyl alkenes. The electrolysis is performed under very simple reaction conditions in an undivided cell using cheap carbon graphite electrodes. This metal-free transformation features broad scope with good to excellent yields. Tertiary, secondary as well as primary alkyl radicals could be easily introduced. α-aminoacids L-aspartic and L-glutamic acid-derived redox active esters were good reactive partners furnishing potentially relevant gem-difluoroalkenes. In addition, it has been demonstrated that our electrosynthetic approach toward the synthesis of gem-difluoroalkenes could use an easily prepared Kratitsky salt as alkyl radical precursor via a deaminative/defluorinative carbofunctionalization of trifluoromethylstyrene.

Photocatalytic Biheterocyclization of 1,7-Diynes for Accessing Skeletally Diverse Tricyclic 2-Pyranones

A new and green route to skeletally diverse oxo-heterocyclic architectures such as pyrano[3,4-c]chromen-2-ones and pyrano[3,4-c]quinolin-2-ones is reported via an unprecedented photocatalytic Kharasch-type cyclization/1,5-(S_N″)-substitution/elimination/6π-electrocyclization/double nucleophilic substitution cascade starting from easily available heteroatom-linked 1,7-diynes and low-cost CBrCl₃. During this reaction process, the full scission of carbon-halogen bonds of BrCCl₃ was realized to directly build two new rings, including a lactone scaffold, using H₂O as the oxygen source of the ester group.