N-Difluoromethylation of imidazoles and pyrazoles using BrCF2PO(OEt)2 under mild condition

A simple and efficient protocol for the direct N-difluoromethylation of imidazoles and pyrazoles has been developed. The reaction makes use of commercially available, non-ozone-depleting and easy handling BrCF₂PO(OEt)₂ as difluorocarbene precursor, and provides a cost-efficient and environmentally benign access to some difluoromethylated biologically relevant molecules.     

Efficient difluoromethylation of isoflavonoids and flavonoid under mild conditions

A simple and efficient protocol for difluoromethylation of isoflavones, flavonoids, and coumarins has been developed. The protocol uses readily available, non-ozone-depleting and easy handling BrCF₂PO(OEt)₂ as difluorocarbene precursor. The reaction underwent the formation of difluorocarbene under mild reaction conditions with relatively weak base therefore demonstrates high selectivity. Application of the reaction led to difluoromethylated biologically relevant molecules.     

Silver‐Catalyzed Oxidative Activation of Benzylic CH Bonds for the Synthesis of Difluoromethylated Arenes

A mild and catalytic method to form difluoromethylated arenes through the activation of benzylic C? H bonds has been developed. Utilizing AgNO₃ as the catalyst, various arenes with diverse functional groups undergo activation/fluorination of benzylic C? H bonds with commercially available Selectfluor reagent as a source of fluorine in aqueous solution. The reaction is operationally simple and amenable to gram‐scale synthesis.     

Silver‐Catalyzed Oxidative Activation of Benzylic C?H Bonds for the Synthesis of Difluoromethylated Arenes

A mild and catalytic method to form difluoromethylated arenes through the activation of benzylic C H bonds has been developed. Utilizing AgNO₃ as the catalyst, various arenes with diverse functional groups undergo activation/fluorination of benzylic C H bonds with commercially available Selectfluor reagent as a source of fluorine in aqueous solution. The reaction is operationally simple and amenable to gram‐scale synthesis.     

Reductive Catalytic Difluorocarbene Transfer via Palladium Catalysis

A palladium-catalyzed reductive difluorocarbene transfer reaction that tames difluorocarbene to couple with two electrophiles has been developed, representing a new mode of difluorocarbene transfer reaction. The approach uses low-cost and bulk industrial chemical chlorodifluoromethane (ClCF₂H) as the difluorocarbene precursor. It produces a variety of difluoromethylated (hetero)arenes from widely available aryl halides/triflates and proton sources, featuring high functional group tolerance and synthetic convenience without preparing organometallic reagents. Experimental mechanistic studies reveal that an unexpected Pd^0/II catalytic cycle is involved in this reductive reaction, wherein the oxidative addition of palladium(0) difluorocarbene ([Pd⁰(L_n)]=CF₂) with aryl electrophile to generate the key intermediate aryldifluoromethylpalladium [ArCF₂Pd(L_n)X], followed by reaction with hydroquinone, is responsible for the reductive difluorocarbene transfer.     

Recent Progress toward the Introduction of Functionalized Difluoromethylated Building Blocks onto C(sp2) and C(sp) Centers

Fluorine chemistry is a field undergoing tremendous expansion. Although much attention has been paid to the introduction of the fluorine atom and the CF₃ group, less interest has been devoted to the introduction of functionalized fluorinated building blocks, in sharp contrast with the high versatility of the fluorinated products. In this Minireview, the most relevant methods for the introduction of difluoromethylated building blocks are summarized. Access to difluoromethylated arenes, alkenes, and alkynes is highlighted and special attention is paid to explanation of the reaction mechanism.     

A General Protocol for C−H Difluoromethylation of Carbon Acids with TMSCF2Br

An efficient method for the selective C‐difluoromethylation of carbon acids with the reagent TMSCF₂Br has been developed. A variety of structurally diverse sp³‐ and sp‐hybridized carbon nucleophiles, including esters, amides, fluorenes, terminal alkynes, β‐ketoesters, malonates, and other activated C?H nucleophiles, could be efficiently and selectively transformed into the corresponding C‐difluoromethylated products under mild conditions. This protocol is also effective for the late‐stage difluoromethylation of pharmaceutically relevant molecules and can be readily scaled up. Moreover, ambident substrates with more than one reactive site towards difluorocarbene can be difluoromethylated orthogonally using TMSCF₂Br.     

Catalytic Enantioselective Cyclopropenation of Internal Alkynes: Access to Difluoromethylated Three‐Membered Carbocycles

Herein we described an efficient Rh^II‐catalyzed enantioselective cyclopropenation reaction of internal alkynes with a masked difluorodiazoethane reagent (PhSO₂CF₂CHN₂, Ps‐DFA). This asymmetric transformation offers efficient access to a broad range of enantioenriched difluoromethylated cyclopropenes (40 examples, up to 99 % yield, 97 % ee). The synthetic utility of obtained strained carbocycles is demonstrated by subsequent stereodefined processes, including cross‐couplings, hydrogenation, Diels–Alder reaction, and Pauson–Khand reaction.     

The reaction of perfluoroalkanesulfonyl halides VIII. A mild method for introducing BrCF2 group to organic molecules

BrCF₂SO₂Br, prepared from sulfinatodehalogenation of CF₂Br₂ followed by bromination of the intermediate BrCF₂SO₂Na, was shown to be a mild and efficient bromodifluoromethylating agent.     

Decarboxylative difluoromethylation of aldehydes with PhSO2CF2COOK: A facile and efficient access to difluoromethylated carbinols

A novel decarboxylative difluoromethylation reaction of PhSO₂CF₂COOK with aldehydes under metal- and ligand-free conditions has been developed. The reaction is very mild and tolerates a wide range of aldehydes (both enolizable and non-enolizable aldehydes), providing a facile and efficient method for the synthesis of structurally diverse difluoromethylated carbinols in moderate to excellent yields.     

Palladium‐Catalyzed Difluoroalkylation of Aryl Boronic Acids: A New Method for the Synthesis of Aryldifluoromethylated Phosphonates and Carboxylic Acid Derivatives

The palladium‐catalyzed difluoroalkylation of aryl boronic acids with bromodifluoromethylphosphonate, bromodifluoroacetate, and further derivatives has been developed. This method provides a facile and useful access to a series of functionalized difluoromethylated arenes (ArCF₂PO(OEt)₂, ArCF₂CO₂Et, and ArCF₂CONR¹R²) that have important applications in drug discovery and development. Preliminary mechanistic studies reveal that a single electron transfer (SET) pathway may be involved in the catalytic cycle.     

Reactions of aliphatic fluoro-alcohols with CHClF2 at atmospheric pressure

The reactions of aliphatic fluoro-alcohols with chlorodifluoromethane (CHClF₂) at atmospheric pressure were examined. In the reaction of CF₃CF₂CH₂OH, the difluoromethylated ether was obtained in moderate yield by using ethers such as 1,4-dioxane, diglyme and THF, or their mixtures with water as a reaction solvent. While acetal and orthoformate were also produced, the selectivity of the difluoromethylated ether could be improved by adding water to the reaction. The effect of water could be explained by the reaction mechanism.     

Kinetics of the reaction F + 1,2-dibromo-1,1,2-trifluoroethane

The title reaction was studied in a standard flow system with F atoms produced by RF discharge in F₂-He mixture. Analysis was by gas chromatography using electron capture detection. There were two major products, identified as CF₂BrCF₂H and CF₂BrCF₂Br, plus presumably HF which was not detectable. The overall rate of disappearance of reactant was found to be of mixed one and one-half order, indicating a complex reaction. A mechanism is proposed comprising six steps and involving two radical species CF₂Br?FBr (R₁) and CF₂Br?F₂. The 300 K rate constant for the initial step F + reactant → HF + R₁ is evaluated to be 2.2 × 10^?13 cm³/molec·s, which fits in with rates of other saturated hydrocarbon reactants containing one hydrogen atom, thus supporting the view that in this class of reactants the rates of reactions of the type F + saturated hydrocarbon depend mainly on the number of hydrogen atoms in the reactant.     

Synthese d'un nouveau monomere hydrofluorocarboxylique le difluoro-2,2-butene-3-oate d'ethyle

The reaction of bromine with chlorotrifluoroethylene yields an addition product BrCF₂CFClBr, which can be further transformed into BrCF₂COOC₂H₅ by hydrolysis with oleum and esterification. The mono adduct ester, BrCH₂CH₂CF₂COOC₂H₅, is selectively obtained by ethylene telomerization in the presence of a radical initiator and ethyl bromodifluoroacetate as telogen; side-addition of two ethylene molecules cannot be completely avoided. The ester was dehydrobrominated with sodium ethanolate, yielding ethyl 2,2 difluoro 3-butenoate, CH₂CH-CF₂COOC₂H₅     

S,O-ligand-promoted palladium-catalyzed C–H olefination of arenes with allylic substrates

An efficient catalytic system for the C–H olefination of arenes with different allylic substrates is reported. The catalytic system is based on Pd(OAc)₂ and a readily accessible bidentate S,O-ligand. The methodology shows high activity with a wide range of arenes, including bulky and, electron-rich and -poor arenes. The applicability of this catalyst is demonstrated in the late-stage functionalization of the complex molecule O-methylestrone.     

Accessing Difluoromethylated and Trifluoromethylated cis‐Cycloalkanes and Saturated Heterocycles: Preferential Hydrogen Addition to the Substitution Sites for Dearomatization

Reported here is a straightforward process in which a cyclic (alkyl)(amino)carbene/Rh catalyst system facilitates the preferential addition of hydrogen to the substitution sites of difluoromethylated and trifluoromethylated arenes and heteroarenes, leading to dearomative reduction. This strategy enables the diastereoselective synthesis of cis‐difluoromethylated and cis‐trifluoromethylated cycloalkanes and saturated heterocycles, and even allows formation of all‐cis multi‐trifluoromethylated cyclic products with a defined equatorial orientation of the di‐ and trifluoromethyl groups. Deuterium‐labeling studies indicate that hydrogen preferentially attacks the substitution sites of planar arenes, resulting in dearomatization, possibly with heterogeneous Rh as the reactive species, followed by either reversible or irreversible hydrogen addition to the nonsubstitution sites.     

Direct Oxidative Coupling of Arenes with Olefins by Rh‐Catalyzed C?H Activation in Air: Observation of a Strong Cooperation of the Acid

A [{RhCl(cod)}₂]/CCl₃COOH system was developed for the oxidative coupling of non‐chelate‐assisted arenes with olefins in the presence of catalytic amounts of Cu(OAc)₂ ? H₂O as a co‐oxidant and oxygen as the terminal oxidant. The acid was an indispensable component in this system and played a very important role in the coupling reaction. This catalytic system was applied to the direct oxidative coupling of a series of arenes and olefins and the corresponding products were afforded in high yields with special chemo‐ and regioselectivity. This reaction provides an atom‐efficient route to vinylarenes, which are widely used in various fine chemicals.     

Gold‐Catalyzed Highly Selective Photoredox C(sp2)−H Difluoroalkylation and Perfluoroalkylation of Hydrazones

The first gold‐catalyzed photoredox C(sp²)?H difluoroalkylation and perfluoroalkylation of hydrazones with readily available R_F?Br reagents is reported. The resulting gem‐difluoromethylated and perfluoroalkylated hydrazones are highly functionalized, versatile molecules. A mild reduction of the coupling products can efficiently produce gem‐difluoromethylated β‐amino phosphonic acids and β‐amino acid derivatives. In mechanistic studies, a difluoroalkyl radical intermediate was detected by an EPR spin‐trapping experiment, indicating that a gold‐catalyzed radical pathway is operating.     

Catalytic Methylation of CH Bonds Using CO2 and H2

Formation of C? C bonds from CO₂ is a much sought after reaction in organic synthesis. To date, other than C? H carboxylations using stoichiometric amounts of metals, base, or organometallic reagents, little is known about C? C bond formation. In fact, to the best of our knowledge no catalytic methylation of C? H bonds using CO₂ and H₂ has been reported. Described herein is the combination of CO₂ and H₂ for efficient methylation of carbon nucleophiles such as indoles, pyrroles, and electron‐rich arenes. Comparison experiments which employ paraformaldehyde show similar reactivity for the CO₂/H₂ system.     

Catalytic Methylation of C?H Bonds Using CO2 and H2

Formation of C C bonds from CO₂ is a much sought after reaction in organic synthesis. To date, other than C H carboxylations using stoichiometric amounts of metals, base, or organometallic reagents, little is known about C C bond formation. In fact, to the best of our knowledge no catalytic methylation of C H bonds using CO₂ and H₂ has been reported. Described herein is the combination of CO₂ and H₂ for efficient methylation of carbon nucleophiles such as indoles, pyrroles, and electron‐rich arenes. Comparison experiments which employ paraformaldehyde show similar reactivity for the CO₂/H₂ system.