Reaction of Diazo Compounds with Difluorocarbene: An Efficient Approach towards 1,1-Difluoroolefins

Hydrocyclization/Defluorination of CF3-Substituted Acrylamides: Insights from Kinetics of Hydrogen Atom Transfer

The introduction of F-containing groups into organic molecules can significantly alter their physical and chemical properties. Particularly, gem-difluoroalkenes serve as versatile precursors for a broad variety of organofluorine compounds, commonly used in agrochemicals, pharmaceuticals, and materials science. Based on the kinetics of H• transfer to acrylamide (kH = 2.28 × 10-4 M-1 s-1 at 300 K in toluene), the study describes a nickel-hydride-(or Li[BEt3H]) initiated hydrocyclization/defluorination of CF3-substituted acrylamides, offering alternative access to 4-fluorovinyl-substituted 2-pyrrolidones (Seletracetam derivatives that are antiepileptic drug candidates). This process proceeds with high yields and remarkable chemo- and regioselectivity. The hydrocyclization/defluorination can be initiated by either H• or H- transfer, followed by a 5-exo-trig cyclization and subsequent fluorine elimination. The strategy has been applied in the late-stage functionalization of drug molecules, providing a valuable tool in the synthesis of pharmaceutical compounds.

α,α-Difluorinated Allylsulfones: gem-Difluoroethylenyl Reagents for Synthesis of Fluorinated Chiral α-Quaternary Amino Acids

Among numerous fluorine-containing molecules, chiral gem-difluoroethylenes (C═CF2) exhibited unique properties in agrochemicals, pharmaceuticals, and materials science. However, the general synthetic methods were limited to the functionalization/defluorination of trifluoromethylalkenes. Here, we disclose a new type of difluoroethylenyl reagent, α,α-difluoro allylsulfones, which allows highly enantioselective Cu-catalyzed desulfonylative SN2' substitution with benzylideneamino esters. This protocol presents a novel strategy for the construction of diversified chiral α-quaternary amino acid derivatives containing a gem-difluoroethylene moiety with excellent results (up to 86% yield, generally 90-98% ee). The ease of synthesis of α,α-difluoro allylsulfones, synthetic applications of this protocol, and transformations of products revealed the potential utility of this chemistry.

General access to furan-substituted gem-difluoroalkenes enabled by PFTB-promoted cross-coupling of ene-yne-ketones and difluorocarbene

Replacement of a carbonyl group with fluorinated bioisostere (e.g., CF2[double bond, length as m-dash]C) has been adopted as a key tactical strategy in drug design and development, which typically improves potency and modulates lipophilicity while maintaining biological activity. Consequently, new gem-difluoroalkenation reactions have undoubtedly accelerated this shift, and conceptually innovative practices would be of great benefit to medicinal chemists. Here we describe an expeditous protocol for the direct assembly of furan-substituted gem-difluoroalkenes via PFTB-promoted cross-coupling of ene-yne-ketones and difluorocarbene. In this multi-step tandem reaction process, the furan ring and the gem-difluorovinyl group are constructed simultaneously in an efficient manner. These products can serve as bioisosteres of the α-carbonyl furan core, which is an important scaffold present in natural products and drug candidates. The broad generality and practicality of this method for late-stage modification of bioactive molecules, gram-scale synthesis and versatile derivatisation of products has been described. Biological activity evaluation showed that the gem-difluoroalkene skeleton exhibited dramatic antitumor activity.

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.

Palladium-catalyzed difluorocarbene transfer enables access to enantioenriched chiral spirooxindoles

We disclose herein an unprecedented Pd-catalyzed difluorocarbene transfer reaction, which assembles a series of structurally interesting chiral spiro ketones with generally over 90% ee. Commercially available BrCF2CO2K serves as the difluorocarbene precursor, which is harnessed as a user-friendly and safe carbonyl source in this transformation. Preliminary mechanistic studies exclude the formation of free CO in the reaction process, and importantly, we also find that BrCF2CO2K outcompete gaseous CO and several common CO surrogates in this asymmetric process. The reaction mechanism, including the in-situ progressive release of the difluorocarbene, the rapid migratory insertion of ArPd(II) = CF2 species, and subsequent defluorination hydrolysis by water to introduce the carbonyl group, accounts for the overall high efficiency and uniqueness. This work clearly showcases the advantage and potential of the difluorocarbene in synthesis and supplies a mechanistically distinct route for asymmetric carbonylative cyclization reactions.

Visible-Light-Driven Synthesis of Dihydroaurones from Aromatic Diazo Compounds

Dihydroaurones, which are derivatives of aurones, exhibit similar biological activity. Although there are many synthetic methods for dihydroaurones, ecofriendly methodologies that circumvent the use of precious metals still need to be explored. In this work, a catalyst-free, visible-light-driven synthesis of dihydroaurones has been developed through the cyclization of aromatic diazo compounds. The reaction proceeded smoothly under mild conditions, resulting in a series of dihydroaurones in moderate to high yields. Mechanistic investigation suggests that this process involves a radical-pair Stevens rearrangement.

Stereodivergent Palladium-Catalyzed C-F Bond Functionalization of gem-Difluoroalkenes

We herein describe a stereodivergent C-F bond functionalization of gem-difluoroalkenes. Using trisubstituted β,β-difluoroacrylates, both E and Z monofluoroalkene products can be obtained with excellent diastereoselectivities. The design of two different reaction manifolds, i.e., Pd(II)- versus Pd(0)-catalyzed cross-coupling of boronic acids, is the key to stereocontrol.

Borane-Catalyzed Coupling of Diazooxindoles and Difluoroenoxysilanes to Tetrasubstituted Monofluoroalkenes

A highly stereoselective coupling reaction of diazooxindoles with difluoroenoxysilanes catalyzed by Lewis acidic boranes has been developed. The reaction proceeded at ambient temperature under transition metal-free conditions with wide functional group tolerance. By using this simple procedure, a series of tetrasubstituted monofluoroalkenes can be accessed in good yield with high selectivity.

Iron(II) Phthalocyanine-Catalyzed Homodimerization and Tandem Diamination of Diazo Compounds with Primary Amines: Access to Construct Substituted 2,3-Diaminosuccinonitriles in One-Pot

We herein first report the homodimerization and tandem diamination of diazo compounds with primary amines catalyzed by the iron(II) phthalocyanine (PcFe(II)), which can construct one C-C bond and two C-N bonds within 20 min in one-pot. Compared to the traditional metal-catalyzed N-H insertion reaction between amines with diazo reagents, the developed reaction almost does not generate the N-H insertion product, but the homodimerization/tandem diamination product. The proposed mechanism studies indicate that primary amines play a crucial role in the homocoupling of diazo compounds via dimerization of iron(III)-acetonitrile radical generated from the reaction between diazoacetonitrile with PcFe(II) coordinated by bis(amines); the β-hydride elimination is involved, and then, the attack of primary amines toward the carbon atoms on the formed C-C bond is followed. Moreover, this novel reaction can be used to effectively prepare substituted 2,3-diaminosuccinonitriles with high yields and even up to >99:1 d.r., encouragingly these products contain both 1,2-diamines and succinonitrile motifs, which are two classes of important organic compounds with significant applications in many yields. This reaction is also suitable for the gram-scale preparation of 2,3-bis(phenylamino)succinonitrile (2a) with a yield of 84%. Therefore, the developed reaction represents a new type of transformation.

Straightforward access to α-carbonyloxy esters and β-keto thioethers from aryldiazoacetates

A metal- and additive-free approach has been described for synthesizing α-carbonyloxy esters and β-keto thioethers from readily available aryldiazoacetates with carboxylic acids and thiol derivatives, respectively. α-Carbonyloxy esters and β-keto thioether derivatives were synthesized in good to high yields from aryldiazoacetates, carboxylic acids, and thiol derivatives decorated with various functional groups. Finally, the potential of the new approach is demonstrated through its application in gram-scale reactions and the synthesis of a few bioactive molecules.

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.

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 of gem-Difluorinated Isoxazoles via Palladium-Catalyzed Oxylallylation of Alkynone Oxime Ethers

A novel and reliable palladium-catalyzed oxylallylation of alkynone oxime ethers with fluorine-containing alkenes was accomplished. Using the bulk industrial chemical 3-bromo-3,3-difluoroprop-1-ene as the coupling partner, this synthetic methodology offers the first example for the assembly of structurally diverse gem-difluorinated isoxazole derivatives in moderate to good yields with high atom- and step-economy and excellent functional group compatibility. More importantly, this strategy allows for the direct combination of the isoxazole motifs and gem-difluoroalkene unit, which is not easy to obtain through a general synthetic strategy.

Base-Mediated α-gem-Difluoroalkenylations of Aldehydes and Ketones

Herein, we present a base-mediated nucleophilic substitution reaction of α-trifluoromethylstyrenes with simple silyl enol ethers, enabling the efficient synthesis of carbonyl-substituted gem-difluoroalkenes. The merit of this protocol is exhibited by its mild reaction conditions, broad substrate scope, and scalable preparation. Notably, this method demonstrates its applicability for late-stage functionalization of structurally complex molecules. Moreover, we illustrate that the resulting products can serve as valuable precursors for the synthesis of diverse medicinally relevant compounds.

Nickel-Catalyzed Cross-Electrophile Ring Opening/gem-Difluoroallylation of Aziridines

Herein we report a nickel-catalyzed regioselective cross-electrophile ring opening reaction of sulfonyl-protected aziridines with trifluoromethyl-substituted alkenes as the gem-difluoroallylating agents, providing a new and efficient entry to prepare gem-difluorobishomoallylic sulfonamides. Moreover, the scaffold of 6-fluoro-1,2,3,4-tetrahydropyridine can be constructed starting from the ring opening products via NaH-mediated intramolecular defluorinative nucleophilic vinylic substitution.

Stereoselective Synthesis of trans-Stilbenes through Silver-Catalyzed Self-Coupling of N-Triftosylhydrazones: An Experimental and Theoretical Study

A silver-mediated homocoupling of N-triftosylhydrazones for the construction of trans-stilbenes has been presented. This protocol is characterized by its suitability for both inter- and intramolecular reactions, operational simplicity, high efficiency with excellent stereoselectivity, broad substrate scope, and good functional group tolerance. A plausible mechanism involving nucleophilic attack of in situ generated sulfonium ylides on silver carbene was proposed on the basis of experimental results and DFT calculations, which further indicates that π-π stacking interactions play a dominant role in stereoselectivity control.

Visible Light-Driven α-Diazoketones as Denitrogenated Synthons: Synthesis of Fluorinated N-Heterocycles via Multicomponent Cyclization Reactions

We disclose herein an efficient photochemical formal [3+2+1] annulation strategy for the transformation of diazocarbonyl compounds into various fluorinated nitrogen-containing heterocycles. This transformation is characterized by reacting fluoroalkyl radicals with α-diazoketones, which are used as infrequent denitrogenated synthons under visible light. Moreover, a wide range of N-heterocycles containing precious CF₃ and perfluoroalkylated groups are constructed in moderate to good yields. Notably, this photochemical strategy may provide a fruitful path for the synthesis of complex organofluorides via diazo/fluorine/radical chemistry.

Iron-Catalyzed Reductive Ring Opening/gem-Difluoroallylation of Cyclopropyl Ketones

By merging C-C and C-F bond cleavage, we developed a regioselective ring opening/gem-difluoroallylation of cyclopropyl ketones with α-trifluoromethylstyrenes, which proceeds under the catalysis of iron with the combination of manganese and TMSCl as the reducing agents, providing a new entry to the synthesis of carbonyl-containing gem-difluoroalkenes. Remarkably, the ketyl radical-induced selective C-C bond cleavage and the following generation of more-stable carbon-centered radicals enable complete regiocontrol of this ring opening reaction for various substitution patterns of the cyclopropane ring.

Photocatalyst-free visible light driven synthesis of gem-dihaloenones from alkynes, tetrahalomethanes and water

Photocatalytic reactions, in particular, processes without photosensitisers, have attracted increased attention due to their green aspect and high economic value and are considered valuable tools in organic synthesis. A new practical photocatalytic system was investigated in this study, and it can efficiently produce gem-dihaloenones by combining terminal alkynes with tetrahalomethanes (BrCCl₃ and CBr₄) and water without a photocatalyst, and the yield can reach up to 87%. The catalytic system is straightforward, the raw materials are inexpensive and easy to obtain, and the operation is simple.

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.

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.

Synthesis of gem-Difluorinated 1,3-Dienes via Synergistic Cu/Pd-Catalyzed Borodifluorovinylation of Alkynes

gem-Difluoroalkenes (=CF₂), which normally act as metabolically stable bioisosteres for carbonyl groups (C═O), are widely applied in agrochemicals and pharmaceuticals and are also used as building blocks in organic synthesis. Herein, an example of Cu/Pd-catalyzed borodifluorovinylation was achieved using alkynes, difluoroethylene bromide, and B₂pin₂ as chemical feedstocks, providing the corresponding conjugated gem-difluoroalkene scaffold with good functional group compatibility. Moreover, an array of fluorinated synthons can be obtained through further transformations.

Light-Mediated Defluorosilylation of α-Trifluoromethyl Arylalkenes through Hydrogen Atom Transfer

Herein, we report a direct, light-mediated defluorosilylation protocol for converting α-trifluoromethyl arylalkenes and alkyl silanes into γ,γ-difluoroallylic compounds via a combination of photoredox catalysis and hydrogen atom transfer. The clean, convenient protocol can be scaled to the gram level, and its mild conditions make it very suitable for late-stage functionalization of complex natural products and drugs.

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.

Application of Aromatic Substituted 2,2,2-Trifluoro Diazoethanes in Organic Reactions

Abstract:

This review provides an overview of metal-, nonmetal-, light-, or catalyst free-promoting reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with organic molecules for the synthesis of trifluoromethyl-substituted compounds. Several approaches will be reviewed and divided into (i) copper-, iron-, Trop(BF4)-, B(C6F5)3-, light-, or rhodium-promoted reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with silanes, amines, mercaptans, phosphonates, p-cyanophenol, benzoic acid, diphenylphosphinic acid, boranes and nBu3SnH, (ii) rhodium-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with amides and phenylhydroxylamine, (iii) copper-, rhodium-, silver-, and light-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with alkynes, (iv) palladium-, copper-, rhodium- and iron-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with alkenes, (v) BF3·OEt2-, copper-, tin- or TBAB-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with HF·Py, (difluoroiodo)toluene (p-TolIF2), TMSCF3, AgSCF3, TMSCF2Br or 1,3-dicarbonyl compounds, (vi) palladium-, copper-, gold/silver- or rhodium-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with indoles, benzene compounds or pyridines, and (vii) palladium-catalyzed reaction of aromatic substituted 2,2,2-trifluoro diazoethanes with benzyl or allyl bromides.

Iron-Catalyzed Allylic Defluorinative Ketone Olefin Coupling

In this protocol, we demonstrate our discovery that iron is able to efficiently catalyze the reductive allylic defluorinative ketyl olefin coupling reaction between α-trifluoromethyl alkenes and unactivated ketones. This operationally simple cross-electrophile reaction circumvents the use of pre-generated organometallics and allows for the synthesis of diverse functional-group-rich tertiary gem-difluorohomoallylic alcohols through a polarity-reversed strategy. Preliminary mechanistic studies support a mechanism that proceeds through a ketyl formation/olefin insertion/β-fluoro elimination sequence.

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.

Direct gem-Difluoroalkenylation of X-H Bonds with Trifluoromethyl Ketone N-Triftosylhydrazones for Synthesis of Tetrasubstituted Heteroatomic gem-Difluoroalkenes

The direct gem-difluoroalkenylation of X-H bonds represents the most straightforward approach to access heteroatomic gem-difluoroalkenes that, as the isostere of the carbonyl group, have great potency in drug discovery. However, the construction of tetrasubstituted heteroatomic gem-difluoroalkenes by this strategy is still an unsolved problem. Here, we report the first direct X-H bond gem-difluoroalkenylation of amines and alcohols with trifluoromethyl ketone N-triftosylhydrazones under silver (for (hetero)aryl hydrazones) or rhodium (for alkyl hydrazones), thereby providing a most powerful method for the synthesis of tetrasubstituted heteroatomic gem-difluoroalkenes. This method features a broad substrate scope, high product yield, excellent functional group tolerance, and operational simplicity (open air conditions). Moreover, the site-specific replacement of the carbonyl group with a gem-difluorovinyl ether bioisostere in drug Trimebutine and the post-modification of bioactive molecules demonstrates potential use in medicinal research. Finally, the reaction mechanism was investigated by combining experiments and DFT calculations, and disclosed that the key step of HF elimination occurred via five-membered ring transition state, and the difference in the electrophilicity of Ag- and Rh-carbenes as well as the multiple intermolecular interactions rendered the effectiveness of Rh catalyst selectively for alkyl hydrazones.

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.

Lewis-Acid-Catalyzed Regioselective Construction of Diversely Functionalized Polycyclic Fused Furans

A novel, facile, and efficient Lewis-acid-catalyzed [4 + 1] annulation protocol for the construction of functionalized polycyclic-fused furans is developed. This methodology is free of transition metals and ligands and provides a rapid synthetic route to divergently orientated polycyclic furans in good yields. In addition, this protocol can also be used to synthesize multisubstituted furans.

Emerging Applications of Aryl Trifluoromethyl Diazoalkanes and Diazirines in Synthetic Transformations

Aryl trifluoromethyl diazoalkanes and diazirines have become unique as reactants in synthetic methodology. As privileged compounds containing CF₃ groups and ease of synthetic access, aryl trifluoromethyl diazoalkanes and diazirines have been highlighted for their versatility in applications toward a wide range of synthetic transformations. This Perspective highlights the synthetic applications of these reactants as precursors of stabilized metal carbenes, i.e., donor-acceptor-substituted ones.

Palladium-catalyzed intramolecular Heck dearomative gem-difluorovinylation of indoles

A palladium-catalyzed dearomative reaction of indoles has been developed through a domino Heck/gem-difluorovinylation sequence. By taking advantage of a difluorocarbene precursor (ClCF₂COONa), the palladium difluorocarbene ([Pd] Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CF₂) species was formed smoothly. Then, a migratory insertion/β-H elimination process enabled access to polycyclic indolines containing 1,1-difluoroethylene units in acceptable yields with a broad substrate scope, which also showed dearomative gem-difluorovinylation for the first time. Remarkably, the superb diversified transformations allowed the product to install various functional groups.

Dearomative gem-difluorovinylation was reported for the first time and provided a new way to construct complex organofluorine compounds rapidly.

Metal-free photocatalytic intermolecular trifluoromethylation-gem-difluoroallylation of unactivated alkenes

An efficient, transition-metal-free, photocatalytic three-component intermolecular trifluoromethylation-gem-difluoroallylation of unactivated alkenes has been achieved.

Nickel-Catalyzed Allylic Defluorinative Cross-Electrophile Coupling with Cycloalkyl Silyl Peroxides as the Alkyl Source

Herein we demonstrate the first successful application of cycloalkyl silyl peroxides (CSP) as an electrophilic coupling partner in the cross-electrophile coupling reaction. Diverse CSP are efficiently cross-coupled with an array of α-trifluoromethyl alkenes under the catalysis of nickel with the assistance of zinc as the reducing agent. This method allows the use of unstrained CSP as the carbonyl-containing alkyl source in the allylic defluorinative reaction, to access a variety of gem-difluoroalkenes bearing a pendent ketone moiety with high functionality tolerance.

Access to gem-Dibromoenones Enabled by Carbon-Centered Radical Addition to Terminal Alkynes in Water Solution

We herein report a novel and more practical approach to prepare gem-dibromoenones from terminal alkynes, tetrabromomethane (CBr₄), and water in a single step. Mechanistic studies reveal that the generation of a tribromomethyl radical with the assistance of a persulfate salt (K₂S₂O₈) is essential to this transformation. The reaction features readily available chemicals, a broad substrate scope, a green solvent, and mild reaction conditions, providing an efficient alternative for construction of halogen-substituted enones.

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.

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.

Asymmetric [3 + 1]-Cycloaddition Reaction via Diazo Discrimination

The enantioselective [3 + 1]-cycloaddition of two structurally different diazo compounds has been achieved using chiral bisoxazoline copper(I) complexes as a catalyst, providing a novel route for the synthesis of cyclobutenes containing a quaternary stereocenter. Typically, this reaction represents the first example of asymmetric cross-electrophile coupling of two diazo substrates via carbene discrimination.

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.

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.