Fluorinated Ylides/Carbenes and Related Intermediates from Phosphonium/Sulfonium Salts

Design and Synthesis of Fluorine-Containing Embedded Carbon Dots Stationary Phase for Separation of Versatile Analytes

Thus far, numerous new stationary phases have been developed. A fluorine-containing embedded carbon dots (F3-CDs-SiO2) stationary phase was first designed and synthesized. The resulting F3-CDs-SiO2 stationary phase was characterized carefully by scanning electron microscopy, transmission electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller experiment. The F3-CDs-SiO2 stationary phase was slurry packed into the HPLC column (150 × 2.1 mm) for evaluation. Furthermore, the F3-CDs-SiO2 column was successfully used for separation of pesticides, nucleosides, sulfonamides, alkaloids, and alkylbenzenes. The retention mechanism (including hydrophobic interaction, F-F, hydrogen bond interaction, ion-exchange, dipole-dipole interaction, electrostatic interaction, etc.) was investigated carefully. Meanwhile, the F3-SiO2 stationary phase was synthesized and used to evaluate the role of CDs. Furthermore, various commercial stationary phases (including amino-SiO2, diol-SiO2, C18-SiO2, and PFP-SiO2) were used for comparison. Moreover, the F3-CDs-SiO2 column possessed good repeatability, reproducibility, and stability in separation of versatile analytes.

Photoinduced Metal-Free Radical Addition/Cyclization of 2-Cyanoaryl Acrylamides to Prepare gem-Difluorinated Naphthyridinone Scaffolds

Direct construction of gem-difluorinated heterocycles represents a long-standing challenge in organic chemistry. Herein, we developed a transition-metal-free photocatalytic radical addition/cyclization of BrCF2COR with 2-cyanoaryl acrylamides to give gem-difluorinated naphthyridinone scaffolds in moderate to good yields. Furthermore, some natural products were found to be suitable in the reaction system. The easily available substrates, mild reaction conditions, simple operation, and wide functionality tolerance show practical and environmental advantages in this method.

A Journey of the Development of Privileged Difluorocarbene Reagents TMSCF2X (X = Br, F, Cl) for Organic Synthesis

ConspectusAs fluorine has played an increasingly important role in modulating the physical, chemical, and biological properties of organic molecules, the selective introduction of fluorine atom(s) or fluorinated moieties into target molecules has become a powerful tool in the development of new pharmaceuticals, agrochemicals, and functional materials. In this context, the difluoromethylene (CF2) and difluoromethyl (CF2H) groups are of special interest because of their ability to serve as bioisosteres of ethereal oxygen atoms and hydroxyl (OH) and thiol (SH) groups, respectively. Difluorocarbene is one of the most versatile reactive intermediates to incorporate CF2 and CF2H groups; however, before 2006, most of the previously known difluorocarbene reagents suffered from several drawbacks such as using ozone-depleting substances (ODSs), difficult-to-handle reagents, or harsh reaction conditions or having narrow substrate scope and/or low yields. Moreover, the reactivity of difluorocarbene generated from different precursors (reagents) was often unpredictable, since the difluorocarbene generation conditions (activation modes) of various difluorocarbene precursors are different, and these conditions may mismatch those required for subsequent difluorocarbene-involved transformations. Therefore, the development of new environmentally friendly and versatile difluorocarbene reagents, as well as the investigation of the mechanistic insights into difluorocarbene-involved reactions, has been highly desirable.In this Account, we summarize our contributions to the development of new difluorocarbene reagents and their applications in organic synthesis since 2006. We have developed seven new difluorocarbene reagents, including 2-chloro-2,2-difluoroacetophenone (1), chlorodifluoromethyl phenyl sulfone (2), S-difluoromethyl-S-phenyl-N-tosylsulfoximine (3), difluoromethyltri(n-butyl)ammonium chloride (4), (chlorodifluoromethyl)trimethylsilane (TMSCF2Cl, 5), (bromodifluoromethyl)trimethylsilane (TMSCF2Br, 6), and (trifluoromethyl)trimethylsilane (TMSCF3, 7). In this journey, we realized the key factor for an ideal difluorocarbene reagent that can be used for a broad range of reactions, that is, the reagent should allow various activation modes for the generation of difluorocarbene species, such as under basic/acidic/neutral conditions, at wide range of temperatures, and in different solvents, which are compatible with a wide range of difluorocarbene-involved transformations. Among all known difluorocarbene reagents, silanes TMSCF2X (X = Br, F, Cl) have stood out as privileged ones, which paves a new avenue for further developing difluorocarbene chemistry. In particular, TMSCF2Br was recognized as an "all-rounder": TMSCF2Br can be applied in almost all common difluorocarbene-involved reactions, and more importantly, TMSCF2Br also enables many other novel transformations that other difluorocarbene reagents cannot achieve, thanks to its unique structure and rich activation modes of releasing difluorocarbene under different reaction conditions. It can be expected that with the commercial availability of TMSCF2X reagents (X = Br, F, Cl) now, the development of difluorocarbene chemistry will be accelerated in the years to come.

Advances in Immunomodulatory MOFs for Biomedical Applications

Given the crucial role of immune system in the occurrence and progression of various diseases such as cancer, wound healing, bone defect, and inflammation-related diseases, immunomodulation is recognized as a potential solution for treatment of these diseases. Immunomodulation includes both immunosuppression in hyperactive immune conditions and immune activation in hypoactive conditions. For these purposes, metal-organic frameworks (MOFs) are investigated to modulate immune responses either by their own bioactivities or by delivering immunomodulatory agents due to their excellent biodegradability and high delivery capacity. This review starts with an overview of the synthesis strategies of immunomodulatory MOFs, followed by a summarization on the latest applications of immunomodulatory MOFs in cancer immunomodulatory, wound healing, inflammatory disease, and bone tissue engineering. A variety of design considerations, in order to optimize immunomodulatory properties and efficacy of MOFs, is also involved. Last, the challenges and perspectives of future research, which are expected to provide researchers with new insight into the design and application of immunomodulatory MOFs, are discussed.

Synthesis of gem-Difluorinated 2,3-Dihydrobenzofurans Using Freon-22 via [4 + 1] Annulation of Difluorocarbene and Antitumor Activity Evaluation

As an inexpensive industrial chemical, chlorodifluoromethane (Freon-22), despite its relatively low reactivity, can serve as a practical CF2 source for the construction of gem-difluorinated ring structures. Here, we develop a protocol for the efficient assembly of valuable fluorinated 2,3-dihydrobenzofurans from the [4 + 1] annulation in good yields under basic conditions. The reliable practicability and scalability of the process have also been demonstrated by preparation at the multigram scale, late-stage modifications of pharmaceutical molecules, and potential antitumor potency.

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.

Copper-Mediated Oxidative Chloro- and Bromodifluoromethylation of Phenols

The first oxidative chloro- and bromodifluoromethylation of phenols with (CH3)3SiCF2X and CuX (X = Cl or Br) in the presence of Selectfluor under mild reaction conditions was developed. This protocol provided a practical and efficient method for the synthesis of a diverse range of biologically valuable and synthetically challenging chloro- and bromodifluoromethyl aryl ethers. Preliminary mechanistic studies suggest that this reaction proceeded through a difluorocarbene-involved oxidative coupling process.

Recent Advances in Monofluorinated Carbenes, Carbenoids, Ylides, and Related Species

The synthesis of monofluorinated compounds is of great interest because of the vast applications of organofluorine compounds. Recently, the introduction of monofluorocarbene synthons has emerged as an important strategy for the synthesis of fluorine-containing products. In contrast to direct fluorination, in which C-F bonds are formed, the use of monofluorinated carbenes and related reactive species involves C-C or C-X bond formation while delivering valuable fluorine atoms into the target structure. Owing to increased knowledge on carbon-carbon and carbon-heteroatom bond formations, monofluorinated carbenes have enormous potential for the synthesis of organofluorine compounds, which, in our opinion, has not yet been fully exploited. This review summarizes the recent advances in the synthetic applications of monofluorinated carbenes, carbenoids, ylides, and related species.

TBAF-Mediated [3+1] Cycloaddition of Difluorocarbene to Access gem-Difluorinated 1,2-Diazetidine Analogues as Potent Anticancer Agents

The facile synthesis of gem-difluorinated 1,2-diazetidines was achieved by metal-free [3+1] annulation between C,N-cyclic azomethine imines with difluorocarbene. A library of 30 compounds benefiting from the TBAF-mediated cyclization process could be directly assembled in moderate to good yield under mild conditions. A plausible mechanism involving the difluorocarbene pathway was proposed based on carbene trapping and control experiments. Many compounds exhibited dramatic antiproliferative activity in 4T1, A549, and HeLa tumor cell lines.

gem-Difluoroolefination of Amides

A metal-free one-pot process for the gem-difluoroolefination of amides is described. The reaction is based on interaction of generated in situ α-chloroiminium salts with difluorinated phosphorus ylide formed from difluorocarbene and triphenylphosphine. The olefination involves nucleophile-assisted dephosphorylation and proceeds within one hour at low temperature. The gem-difluoroenamines were used in further transformations leading to a variety of fluoroalkylated amines.

Tunable Synthesis of Monofluoroalkenes and Gem-Difluoroalkenes via Solvent-Controlled Rhodium-Catalyzed Arylation of 1-Bromo-2,2-difluoroethylene

Divergent synthesis of fluorine-containing scaffolds starting from a suite of raw materials is an intriguing topic. Herein, we report the solvent-controlled rhodium-catalyzed tunable arylation of 1-bromo-2,2-difluoroethylene. The selection of the reaction solvents provides switchable defluorinated or debrominated arylation from readily available feedstock resources (both arylboronic acids/esters and 1-bromo-2,2-difluoroethylene are commercially available). This switch is feasible because of the difference in coordination ability between the solvent (CH2 Cl2 or CH3 CN) and the rhodium center, resulting in different olefin insertion. This protocol allows the convenient synthesis of monofluoroalkenes and gem-difluoroalkenes, both of which are important scaffolds in the fields of medicine and materials. Moreover, this newly developed solvent-regulated reaction system can be applied to the site-selective dechlorinated arylation of trichloroethylene. Overall, this study provides a useful strategy for the divergent synthesis of fluorine-containing scaffolds and provides insight into the importance of solvent selection in catalytic reactions.

Synthesis and Functionalization of Thiophosphonium Salts: A Divergent Approach to Access Thioether, Thioester, and Dithioester Derivatives

Herein, we report a straightforward practical method for efficiently obtaining a diverse range of thiophosphonium salts. This method involves the direct coupling of commercially available thiols and aldehydes with Ph3P and TfOH. The setup is simple and carried out in a metal-free manner. The synthetic utility of these salts is demonstrated through various examples of C-P bond functionalizations, enabling the synthesis of thioether, deuterated thioether, thioester, and dithioester derivatives. These products, which serve as valuable building blocks, are obtained in high yields.

Photoredox Catalysis-Enabled C-H Difluoromethylation of Heteroarenes with Pentacoordinate Phosphorane as the Reagent

Difluoromethylated heterocyclic compounds have found broad applications in numerous bioactive molecules. Herein, we report photoredox catalysis-induced direct C-H difluoromethylation of heterocycles by using bis(difluoromethyl) pentacoordinate phosphorane (PPh3(CF2H)2, 1) as the reagent. A variety of heterocycles, such as quinoxalin-2(1H)-one, thiophene, indole, and coumarin, are readily tailored with a difluoromethyl group. The method is featured as transition-metal-free by using an organic compound Erythrosin B as the catalyst and O2 as the oxidant.

Recent developments in the cleavage, functionalization, and conjugation of proteins and peptides at tyrosine residues

Peptide and protein selective modification at tyrosine residues has become an exploding field of research as tyrosine constitutes a robust alternative to lysine and cysteine-targeted traditional peptide/protein modification protocols. This review offers a comprehensive summary of the latest advances in tyrosine-selective cleavage, functionalization, and conjugation of peptides and proteins from the past three years. This updated overview complements the extensive body of work on site-selective modification of peptides and proteins, which holds significant relevance across various disciplines, including chemical, biological, medical, and material sciences.

Transition-Metal-Free Controllable Single and Double Difluoromethylene Formal Insertions into C-H Bonds of Aldehydes with TMSCF2 Br

We have developed a new strategy for controllable single and double difluoromethylene (CF₂ ) formal insertions into C-H bonds of aldehydes with nearly full selectivity under transition-metal-free conditions. The key to the success of controllable CF₂ insertions lies in the well-defined formation of 2,2-difluoroenolsilyl ether and 2,2,3,3-tetrafluorocyclopropanolsilyl ether intermediates using difluorocarbene reagent TMSCF₂ Br (TMS=trimethylsilyl). These two intermediates can react with various electrophiles including proton sources and various halogenation reagents, allowing for the access to diverse arrays of ketones containing difluoromethylene (CF₂ ) and tetrafluoroethylene (CF₂ CF₂ ) units. The first synthesis of relatively stable 2,2,3,3-tetrafluorocyclopropanolsilyl ethers has been achieved, which offers a new platform to explore other unknown chemical space.

Direct formylation of phenols using difluorocarbene as a safe CO surrogate

A convenient method to prepare aryl formates is reported herein that exploits difluorocarbene to serve as a CO surrogate. This reaction is proposed to occur through a sequential O-difluoromethylation of phenol, followed by α-C-F bond functionalization of the resulting aryl difluoromethyl ether intermediate by phenol or moisture through fluorosemiacetal or orthoformate intermediates. Late-stage modification of biologically and materially active compounds is demonstrated.

Difluorocarbene-Triggered Acyl Rearrangement Reaction: A Strategy for the Direct Introduction of the gem-Difluoromethylene Group

A novel metal- and catalyst-free dearomative reaction of 2-oxypyridines to construct gem-difluoromethylenated N-substituted 2-pyridones has been developed. The reaction involves an attractive acyl rearrangement from O to CF₂ of difluorocarbene-derived pyridinium ylides, which provides a new strategy for the direct introduction of the gem-difluoromethylene group with high efficiency and selectivity as well as broad substrate scope. Gram-scale synthesis and synthetic transformations have also been demonstrated.

Access to cyclopropanes with geminal trifluoromethyl and difluoromethylphosphonate groups

A synthetic route to the bench-stable fluorinated masked carbene reagent diethyl 2-diazo-1,1,3,3,3-pentafluoropropylphosphonate, bearing a trifluoromethyl and a difluoromethyl group is reported for the first time. Its application in CuI-catalyzed cyclopropanation reactions with aromatic and aliphatic terminal alkenes under mild reaction conditions is demonstrated. In total, sixteen new cyclopropanes were synthesized in good to very good yields.

Synthesis of Carbamoyl Fluorides Using a Difluorophosgene Surrogate Derived from Difluorocarbene and Pyridine N-Oxides

We report a method for the synthesis of carbamoyl fluorides from secondary amines using bench-stable, inexpensive, and readily accessible starting materials that, when combined, yield a surrogate for toxic difluorophosgene (COF₂) gas. In contrast to state-of-the-art methods for the synthesis of carbamoyl fluorides, our protocol does not require the use of pre-functionalized substrates, the preparation of light-, temperature-, and/or moisture-sensitive chemicals, or the application of explosive fluorinating reagents.

Palladium-Catalyzed Regioselective [5 + 1] Annulation of Vinyl Aziridines/Epoxides with ClCF2COONa

Palladium-catalyzed regioselective [5 + 1] annulation reactions of vinyl aziridines/epoxides with ClCF₂COONa have been developed. Significantly, vinyl aziridines/epoxides act as heteroatom-containing five-atom synthons, and commercially available and cheap ClCF₂COONa acts as the source of carbonyl serving as a difluorocarbene precursor. This protocol provides an efficient and practical method for the synthesis of δ-lactams and δ-lactones in good yields.

Metal-free synthesis of gem-difluorinated heterocycles from enaminones and difluorocarbene precursors

A cascade strategy to synthesise gem-difluorinated 2H-furans from reactions of BrCF₂CO₂Et with enaminones has been described. The reactions tolerate a wide variety of functional groups under metal-free conditions. An active aminocyclopropane is proposed to be a key intermediate through the cyclopropanation of difluorocarbene with enaminones, which further triggers a regioselective C-C bond cleavage in situ to afford the corresponding gem-difluorinated 2H-furans.

anti-Markovnikov Iodofluorination of Alkenes

The fluorination of alkenes with electrophilic N-F type reagents usually occurs through a Markovnikov-type addition, and the anti-Markovnikov-type addition may require the use of a transition metal catalyst or an expensive catalyst. Herein we describe a convenient anti-Markovnikov iodofluorination of alkenes with Selectfluor/ nBu4NI. A wide substrate scope and good functional group tolerance were observed. The process allows for the construction of various C-F bonds, especially tertiary C-F bonds. The remarkable features make this protocol attractive, including convenient operations, simple reaction conditions, and the installation of an iodine atom which provides possibilities for further transformations.

Facile access to the 2,2-difluoro-2,3-dihydrofuran skeleton without extra additives: DMF-promoted difluorocarbene formation of ClCF2CO2Na

A practical and facile difluorocarbene-triggered cycloaddition reaction of enaminones was developed, which delivered 2,2-difluoro-2,3-dihydrofurans without any extra additives.

Synthesis of oxindoles bearing a stereogenic 3-fluorinated carbon center from 3-fluorooxindoles

3,3-Disubstituted oxindoles bearing a stereogenic 3-fluorinated carbon center are privileged structural motifs present in many bioactive molecules. The straightforward functionalization of 3-fluorooxindoles constitutes a powerful method for the synthesis of 3-fully substituted 3-fluorooxindoles, taking advantage of the ease of preparation of 3-fluorooxindoles with different substitution patterns and the atom efficiency of chemical reactions. In the past decade, many papers have appeared on the synthesis of 3-fully substituted 3-fluorooxindoles from 3-fluorooxindoles. Importantly, many asymmetric catalytic methods have been developed for the enantioselective synthesis of these valuable compounds. This review summarizes the achievements in this area, and overviews synthetic opportunities that still exist.

TMSCF2 Br-Enabled Fluorination-Aminocarbonylation of Aldehydes: Modular Access to α-Fluoroamides

A protocol for the modular assembly of the α-fluoroamide motif has been developed, which provides a practical method for the efficient synthesis of structurally diverse α-fluoroamides from easily available aldehydes and tertiary amines through a three-component fluorination-aminocarbonylation process. The key to the success of this process is taking advantage of the multiple roles of the unique difluorocarbene reagent TMSCF₂ Br (TMS=trimethylsilyl). The mechanism of the process involves the 1,2-fluorine and oxygen migrations of the in situ formed TMS-protected α-aminodifluoromethyl carbinol intermediates, which represents a new type of deoxyfluorination reaction.

Starting from Styrene: A Unified Protocol for Hydrotrifluoromethylation of Diversified Alkenes

In contrast with unactivated alkenes, the corresponding hydrotrifluoromethylation of styrene has remained challenging due to the strong propensity of styrene for oligomerization and polymerization. On the basis of our newly developed trifluoromethylation reagent, TFSP, herein we present a general method for the hydrotrifluoromethylation of styrene under photoredox catalysis. The substrate scope was further extended to unactivated alkenes, acrylates, acrylamides, and vinyl-heteroatom-substituted alkenes. The tunability of this method was showcased via the relevant deprotonative trifluoromethylation and trifluoromethyltrifluoroethoxylation reactions.

Difluorocarbene-Induced Ring-Opening Difluoromethylation-Halogenation of Cyclic (Thio)Ethers with TMSCF2 X (X=Br, Cl)*

The ring-opening difluoromethylation-halogenation of cyclic (thio)ethers is reported through a simple strategy relying on carbon-chalcogen bond activation with difluorocarbene. The reaction proceeds through in situ protonation of the previously little-known difluoromethylene oxonium or sulfonium ylide intermediate followed by ring-opening with halide ion to afford halogenated acyclic difluoromethyl (thio)ethers that can then be employed for further elaboration. TMSCF₂ X (X=Br, Cl) are unique reagents to achieve this synthetic purpose, which serve as both the difluorocarbene source and the halide ion source.

HCF2Se/HCF2S Installation by Tandem Substitutions from Alkyl Bromides

Herein we describe an efficient construction of HCF₂Se and HCF₂S groups by tandem substitutions between alkyl bromides and a reagent system consisting of MSeCN (or MSCN) and Ph₃P⁺CF₂H Br^-. The tandem process occurs via the first nucleophilic substitution of alkyl bromides by -SeCN (or -SCN) and the subsequent nucleophilic difluoromethylation.

Transition-metal difluorocarbene complexes

Although transition metal carbenes have found widespread applications and difluorocarbene has served as a versatile intermediate, it is still quite challenging to make use of transition-metal difluorocarbenes in synthetic chemistry due to their unpredictable reactivities. In this Highlight, we review recent developments in the transition-metal-catalyzed or -mediated transfer of difluorocarbene and the reactivies and conversions of transition-metal difluorocarbene complexes. We start with the MCF₂ bonding, then provide the progress in the transfer of difluorocarbene, and finally briefly discuss the conversions of MCF₂ into other metal complexes. The understanding of the interesting reactivities of MCF₂ may help design the catalytic transfer of difluorocarbene for various reactions.

Visible-Light-Induced Selective Photolysis of Phosphonium Iodide Salts for Monofluoromethylations

The sigma (σ)-hole effect has emerged as a promising tool to construct novel architectures endowed with new properties. A simple yet effective strategy for the generation of monofluoromethyl radicals is a continuing challenge within the synthetic community. Fluoromethylphosphonium salts are easily available, air- and thermally stable, as well as simple-to-handle. Herein, we report the ability of the σ-hole effect to facilitate the visible-light-triggered photolysis of phosphonium iodide salts, a charge-transfer complex, selectively giving fluoromethyl radicals. The usefulness and versatility of this new protocol are demonstrated through the mono-, di-, and trifluoromethylation of a variety of alkenes.

A Readily Available Trifluoromethylation Reagent and Its Difunctionalization of Alkenes

Trifluoromethyl substitution is notably popular in pharmaceuticals and agrochemicals; however, trifluoromethylated compounds normally rely on the use of cost-prohibitive or gaseous trifluoromethylating reagents, which diminishes the general applicability of these methods. Herein an efficient trifluoromethylation reagent trifluoromethylsulfonyl-pyridinium salt (TFSP) was reported, which can be readily prepared from cheap and easily available bulk industrial feedstocks. TFSP can generate a trifluoromethyl radical under photocatalysis and realize the effective azido- or cyano-trifluoromethylation reactions of alkenes.

Rh-catalyzed tunable defluorinative borylation

Described herein is a Rh-catalyzed tunable defluorinative borylation of allylic gem-difluorides to provide allylborylated monofluoroalkenes or homoallylborylated monofluoroalkenes with excellent Z/E selectivities. Completely different reaction paths were observed by slightly changing the reaction conditions. Allylborylated monofluoroalkenes were further converted into dihydroxyl-containing monofluoroalkenes.

Wonderful fusion of organofluorine chemistry and decarboxylation strategy

Decarboxylation strategy has been emerging as a powerful tool for the synthesis of fluorine-containing organic compounds that play important roles in various fields such as pharmaceuticals, agrochemicals, and materials science. Considerable progress in decarboxylation has been made over the past decade towards the construction of diverse valuable fluorinated fine chemicals for which the fluorinated part can be brought in two ways. The first way is described as the reaction of non-fluorinated carboxylic acids (and their derivatives) with fluorinating reagents, as well as fluorine-containing building blocks. The second way is dedicated to the exploration and the use of fluorine-containing carboxylic acids (and their derivatives) in decarboxylative transformations. This review aims to provide a comprehensive summary of the development and applications of decarboxylative radical, nucleophilic and cross-coupling strategies in organofluorine chemistry.

Synthesis of Difluorinated Heterocyclics through Metal-Free [8+1] and [4+1] Cycloaddition of Difluorocarbene

With Ph₃P⁺CF₂COO^- or TMSCF₂Br as the difluorocarbene sources, a facile metal-free cycloaddition between heteroconjugated alkenes and difluorocarbene was developed for the highly convergent synthesis of novel difluorinated heterocyclics, including gem-difluorinated azetidines and 2,3-dihydrobenzofurans. The cycloaddition features high reactivity and regioselectivity, as well as good tolerance of various electron-donating or electron-withdrawing substituents on azaheptafulvenes and o-quinone methides.

Difluorocarbene-based cyanodifluoromethylation of alkenes induced by a dual-functional Cu-catalyst

Although cyanofluoroalkylation has received increasing attention, a toxic cyanation reagent is usually required. Herein, a Cu-catalyzed difluorocarbene-based cyanodifluoromethylation of alkenes with BrCF2CO2Et/NH4HCO3 under photocatalytic conditions is described. BrCF2CO2Et and NH4HCO3 serve as a carbon source and a nitrogen source of the nitrile group, respectively, avoiding the use of a stoichiometric toxic cyanation reagent. The Cu-complex plays a dual role. It is not only a photocatalyst, but also a coupling catalyst for the formation of a C-CN bond.