A General Protocol for C−H Difluoromethylation of Carbon Acids with TMSCF 2 Br

Difluorocarbene Enables Access to 2,2-Difluorohydrobenzofurans and 2-Fluorobenzofurans from ortho-Vinylphenols

2-Fluorobenzofurans are the backbone structures of many drug molecules and have many potential therapeutic bioactivities. Despite the potential applications in medicinal chemistry, practical and efficient synthetic methods for the construction of 2-fluorobenzofuran are very limited. Herein, we report an efficient and general method for the construction of 2-fluorobenzofurans. Contrary to the previous functionalizations of the existing backbone of benzofuran, our strategy directly constructs benzofuran scaffolds alongside the incorporation of fluorine atom on C2 position in a formal [4 + 1] cyclization from readily accessible ortho-vinylphenols and difluorocarbene. In our strategy, ClCF2H decomposes into difluorocarbene in the presence of base, which is further captured by the oxygen anion from the hydroxy group in ortho-hydroxychalcones; subsequent intramolecular Michael addition to the α, β-unsaturated system leads to 2,2-difluorohydrobenzofurans, and further fluorine elimination renders 2-fluorobenzofurans by forming one C-O bond and one C-C double bond. Of note, various complex 2,2-difluorohydrobenzofurans and 2-fluorobenzofurans could be readily accessed through our protocol via the late-stage elaborations.

Controllable Double Difluoromethylene Insertions into S-Cu Bonds: (Arylthio)tetrafluoroethylation of Aryl Iodides with TMSCF2Br

A new method of constructing "ArSCF2CF2Cu" from ArSCu and TMSCF2Br (TMS=trimethylsilyl) has been developed. The cross-coupling reactions of the obtained "ArSCF2CF2Cu" with diverse aryl iodides (Ar'I) provide an efficient access to Ar'CF2CF2SAr. Mechanistic studies demonstrate that the "ArSCF2CF2Cu" species were generated through controllable double difluoromethylene insertions into ArS-Cu bonds rather than the 1,2-addition of ArSCu to tetrafluoroethylene.

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.

Controllable Fluorocarbon Chain Elongation: TMSCF2Br-Enabled Trifluorovinylation and Pentafluorocyclopropylation of Aldehydes

Controllable fluorocarbon chain elongation (CFCE) is a promising yet underdeveloped strategy for the well-defined synthesis of structurally novel polyfluorinated compounds. Herein, the direct and efficient trifluorovinylation and pentafluorocyclopropylation of aldehydes are described by using TMSCF2Br (TMS = trimethylsilyl) as the sole fluorocarbon source, accomplishing the goals of CFCE from C1 to C2 and from C1 to C3, respectively. The key to the success of these CFCE processes lies in the unique and diversified chemical reactivity of TMSCF2Br, which can serve as two different precursors, namely, a TMSCF2 radical precursor and a difluorocarbene precursor. Various functional groups are amenable to this new synthetic protocol, providing streamlined access to a broad range of alcohols containing trifluorovinyl or pentafluorocyclopropyl moieties from abundantly available aldehydes. The potential utility of these methods is further demonstrated by the gram-scale synthesis, derivatization, and measurement of log P values of the products.

Oxidant- and Base-Free, Copper-Catalyzed Difluoromethylation of Haloalkynes

We report herein a highly efficient copper-catalyzed protocol for the transformation of haloalkynes to the corresponding difluoromethylated alkynes. This scalable protocol exhibits a broad substrate scope and excellent functional group tolerance, enabling the late-stage difluoromethylation of bioactive molecules. Additionally, the strategy of utilizing the difluoromethylalkynes in gram-scale reactions and multiple transformations has proven to be highly valuable in synthetic chemistry.

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.

Visible-Light-Induced Desaturative β-Alkoxyoxalylation of N-Aryl Cyclic Amines with Difluoromethyl Bromides and H2O Via a Triple Cleavage Process

A visible-light-driven desaturative β-alkoxyoxalyation of N-aryl cyclic amines with difluoromethyl bromides and H2O has been reported. This tandem reaction is triggered by homolysis of the C-Br bond to produce the difuoroalkyl radical, which undergoes the subsequent defluorinated β-alkoxyoxalylation cascades to afford a wide range of β-ketoester/ketoamides substituted enamines. The prominent feature of this reaction contains photocatalyst-free, transition-metal free, and mild conditions. The 18O labeling experiment disclosed that H2O is the oxygen source of the carbonyl unit.

Divergent Construction of Thiochromanes and N-Arylbutanamides via Arylthiodifluoromethyl Radical-Triggered Cascade of Alkenes

A strategy utilizing silver-catalyzed oxidative decarboxylation radical cascade cyclization of arylthiodifluoroacetic acids with alkenes for the simple and efficient preparation of difluoromethylated thiochromanes and 2,2-disubstituted-N-arylbutanamides derivatives has been developed. This approach includes good functional group tolerance, easily accessible starting materials, and operational simplicity.

(Z)-Selective Synthesis of Bromofluoroalkenes via the TMSCF2Br-Mediated Tandem Reaction with para-Quinone Methides

We report herein a tandem reaction of para-quinone methides with TMSCF₂Br to construct bromofluoroalkenes in a Z-selective manner. While TMSCF₂Br has been documented as the precursor of difluoro carbene, it exhibits another possibility in this transformation, a formal bromofluoro carbene surrogate. The alkenyl bromide unit of the products could directly engage in a variety of transformations.

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.

Copper-Catalyzed Synthesis of Difluoromethyl Alkynes from Terminal and Silyl Acetylenes

An efficient method for the direct C(sp)-H difluoromethylation of terminal alkynes and the desilylation-difluoromethylation of (trimethylsilyl)acetylenes is disclosed. The copper-catalyzed transformation provides access to a wide range of structurally diverse CF₂H alkynes in good yields, utilizing a (difluoromethyl)zinc reagent and an organic oxidant. The difluoromethylation of important synthons and API's is showcased. The synthetic utility of these (difluoromethyl)alkynes is demonstrated by selected cycloaddition reactions. Additionally, a slight modification to the reaction conditions allowed the selective preparation of a 2-difluoromethylindole.

Radical hydrodifluoromethylation of unsaturated C-C bonds via an electroreductively triggered two-pronged approach

Due to its superior ability in controlling pharmaceutical activity, the installation of difluoromethyl (CF₂H) functionality into organic molecules has been an area of intensive research. In this context, difluoromethylation of C-C π bonds mediated by a CF₂H radical have been pursued as a central strategy to grant access to difluoromethylated hydrocarbons. However, early precedents necessitate the generation of oxidative chemical species that can limit the generality and utility of the reaction. We report here the successful implementation of radical hydrodifluoromethylation of unsaturated C-C bonds via an electroreductively triggered two-pronged approach. Preliminary mechanistic investigations suggest that the key distinction of the present strategy originates from the reconciliation of multiple redox processes under highly reducing electrochemical conditions. The reaction conditions can be chosen based on the electronic properties of the alkenes of interest, highlighting the hydrodifluoromethylation of both unactivated and activated alkenes. Notably, the reaction delivers geminal (bis)difluoromethylated products from alkynes in a single step by consecutive hydrodifluoromethylation, granting access to an underutilized 1,1,3,3-tetrafluoropropan-2-yl functional group. The late-stage hydrodifluoromethylation of densely functionalized pharmaceutical agents is also presented.

Controllable Single and Double Difluoromethylene Insertions into C-Cu Bonds: Copper-Mediated Tetrafluoroethylation and Hexafluoropropylation of Aryl Iodides with TMSCF2H and TMSCF2Br

The selective difluoromethylene insertion into a C-Cu bond is a challenging task and is currently limited to either a single CF₂ insertion into CuCF₃ or double CF₂ insertions into CuC₆F₅ (or (Z)-CF₃CF = CFCu). Achieving both selective single and double CF₂ insertions into the same C-Cu bond is even more difficult. Herein, highly controllable single and double CF₂ insertions into CuCF₂H species with a TMSCF₂Br reagent have been described, affording two previously unknown fluoroalkylcopper species "Cu(CF₂)_nCF₂H" (n = 1 and 2) independently under different reaction conditions. This work represents the first example of both single and double CF₂ insertions into the same C-Cu bond in a highly selective manner. The synthetic value of the obtained "Cu(CF₂)_nCF₂H" (n = 1 and 2) species is demonstrated by their reactions with aryl iodides, halogenation agents, and cinnamyl chloride, which enables the direct transfer of HCF₂CF₂ and HCF₂CF₂CF₂ moieties into organic molecules. The key to controllable fluorocarbon chain elongation from C₁ to C₂ and from C₁ to C₃ is presumably attributed to the different reactivities of "Cu(CF₂)_nCF₂H" species (n = 0, 1, 2 and 3) and the loading of the TMSCF₂Br reagent.

Synthesis of Aryl Perfluorocyclopropyl Ethers via [2 + 1] Cyclopropanation Using TMSCF2Br Reagent

Aryl perfluorocyclopropyl ethers have been synthesized for the first time by [2 + 1] cyclopropanation between aryl trifluorovinyl ethers and a commercially available TMSCF₂Br reagent. This cycloaddition reaction between two fluorine-containing reactants proceeds smoothly in toluene at 120 °C in the presence of a catalytic amount of n-Bu₄NBr, and the reaction tolerates a variety of functional groups. A wide range of aryl trifluorovinyl ethers, easily accessible from phenols, were successfully transformed to aryl perfluorocyclopropyl ethers.

Fluoride Anion Catalyzed Mukaiyama-Aldol Reaction: Rapid Access to α-Fluoro-β-hydroxy Esters

The Mukaiyama-aldol reaction is probably one of the most efficient strategies to prepare synthetically useful β-hydroxy carbonyl compounds. However, only several reported methods were concerned with the accesses to α-fluoro-β-hydroxy esters. Herein, we report a protocol for a fluoride anion-mediated Mukaiyama aldol reaction with low catalytic loading in a short reaction time to incorporate fluorine at the α position into β-hydroxy esters. The method shows good functional-group tolerance and scale-up potential, moreover, is applicable to the late-stage modification of natural products and small molecular drugs.

Direct C(sp3)−H Difluoromethylation via Radical-Radical Cross-Coupling by Visible-Light Photoredox Catalysis

Herein, the radical-radical cross-coupling strategy for direct difluoromethylation of C(sp3)−H bond is reported. This transformation was readily accomplished under transition metal-free photoredox catalysis in the presence of 3 mol% of...

Ruthenium-catalyzed meta-difluoromethylation of arene phosphines enabled by 1,3-dione

A highly efficient, meta-selective difluoromethylation of arene phosphines has been developed with ruthenium catalysis using 1,3-dione as an effective ligand.

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.

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.

Catalyst-free gem-chlorosulfurization of difluoromethyl-substituted diazo compounds with disulfide and PhICl2

A series of gem-chlorosulfurization products bearing difluoromethyl substituents were synthesized in high to excellent yields directly from p-toluenesulfonyl difluorodiazoethane (TsCF₂CHN₂), disulfides and PhICl₂ without any catalysts or additives. The mild reaction conditions and high functional group compatibility indicated the utility and sustainability of the method. In addition, the gem-chlorosulfurization products could be efficiently converted to sulfur-containing and aryl substituted difluoromethyl derivatives by a feasible multi-component operation.

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.

Chemoselective N- and O-Difluoromethylation of 2-Pyridones, Isoquinolinones, and Quinolinones with TMSCF2Br

An operationally simple protocol for direct N- and O-difluoromethylation of 2-pyridones, quinolinones, and isoquinolinones using commercially available TMSCF₂Br is disclosed. The chemoselectivity is modulated by simple variations in temperature, solvent, and strength of the base. Diverse, synthetically relevant functional groups are tolerated, including functional groups that have reported reactivity with TMSCF₂Br. Gram-scale reactions to prepare both N- and O-difluoromethyl compounds are included.

Base promoted gem-difluoroolefination of alkyl triflones

A new synthesis of gem-difluoroalkenes from readily available alkyl triflones and difluorocarbene precursors such as TMSCF₂Br has been reported. The reaction, regardless of electronic effect, gives gem-difluoroalkenes in good to excellent yields. The mechanism may involve deprotonation of triflones, nucleophilic addition, and the elimination of SO₂CF₃.

Copper-Catalyzed Enantioselective Difluoromethylation of Amino Acids via Difluorocarbene

Difluoromethyl amino acids (DFAA) exhibit intriguing biological properties, making them highly desirable motifs in agrochemical and pharmaceutical science. However, stereochemical control of direct difluoromethyl transformation via the difluorocarbene species has not been demonstrated. Here we describe an efficient copper-catalyzed asymmetric difluoromethylation reaction that systematically delivers chiral DFAA as rationally designed mechanism-based inhibitors of PLP-dependent amino acid decarboxylases. The reaction employs difluoromonochloromethane, an abundant raw material, as the direct precursor of difluorocarbene species, enabling the unprecedentedly direct conversion of amino esters into corresponding valuable DFAA products in good yields with excellent enantioselectivities. This de novo synthesis creates opportunities to integrate an asymmetric catalytic platform for the preparation of diverse libraries of biologically important DFAA derivatives and will support efforts in both drug discovery and development.

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.

Modern approaches towards the synthesis of geminal difluoroalkyl groups

This review will cover the importance of and most recent approaches toward geminal difluoroalkyl groups. Transition metal-mediated, photochemical, organocatalytic, and other methods as well as their mechanistic implications will be discussed, with special emphasis on applications to biologically-relevant compounds.

Difluoromethylation of Alkyl Bromides and Iodides with TMSCF2H

We describe, for the first time, two protocols for direct difluoromethylation of unactivated alkyl bromides and iodides. Reactions of alkyl iodides with TMSCF₂H were mediated by a copper catalyst using CsF as the activator, while reactions of less reactive alkyl bromides required a combination of palladium and a stoichiometric amount of CuI as the catalysts. Preliminary mechanistic studies of the synergistic Pd/Cu-catalyzed difluoromethylation of alkyl bromides suggest that it proceeds likely via a Pd(I)/Pd(III) catalytic cycle.

Late-stage difluoromethylation: concepts, developments and perspective

This review describes the conceptual advances that have led to the multiple difluoromethylation processes making use of well-defined CF₂H sources.

Slicing and Splicing of Bromodifluoro-N-arylacetamides: Dearomatization and Difunctionalization of Pyridines

Copper-catalyzed dearomatization and difunctionalization of pyridines have been disclosed, in which bromodifluoro-N-arylacetamide was sliced into five fragments and three or four of them were transferred to pyridine partners. Through this reaction, novel N-difluoromethyl-2-imine dihydropyridine derivatives can be conveniently accessed from commercially available 4-amino substituted pyridines. This strategy demonstrates a novel fluorination method featuring high atom economy, environmental friendliness, an easily available catalyst, and simple operation.

Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers

A method for the light-mediated fluoroalkylation of silyl enol ethers with (bromodifluoromethyl)trimethylsilane followed by a reduction of the primary products with sodium borohydride is described. An 18 W, 375 nm LED was used as the light source. The reaction is performed in the presence of a gold photocatalyst, which effects the generation of a (trimethylsilyl)difluoromethyl radical via cleavage of the carbon–bromine bond.

The difluoromethylthio moiety lowers the LCST of oligo(ethylene glycol)-based homopolymers

Introduction of difluoromethylthio moiety could significantly lower LCSTs of oligo(ethylene glycol)-based thermo-responsive homopolymers.

Practical fluorothiolation and difluorothiolation of alkenes using pyridine-HF and N-thiosuccinimides

Fluorothiolation and difluorothiolation of alkenes using pyridine-HF and N-thiosuccinimides.

Ex Situ Generation of Difluorodiazoethane (CF2HCHN2): Application in the Regioselective Synthesis of CF2H-Containing Pyrazoles

A new method for the ex situ generation of difluorodiazoethane (CF₂HCHN₂) and a procedure for its efficient use in [3 + 2] cycloaddition with nitroolefins by the AcOH/O₂ catalyst system were developed by using a simple two-chamber system. The method provides a facile and straightforward access to a series of 4-substituted 5-difluoromethyl-3-nitro-1H-pyrazoles that are of interest in medicinal chemistry. Interestingly, the key factor for the success of this method is the efficient preparation of CF₂HCHN₂ by an ex situ process.

Highly chemoselective difluoromethylative homologation of iso(thio)cyanates: expeditious access to unprecedented α,α-difluoro(thio)amides

The new motif - α,α-difluoromethyl thioamide - has been assembled starting from isothiocyanate (as thioamide precursor) and a formal difluoromethyl-carbanion generated from commercially available TMSCHF2. Upon proper activation of this reagent with potassium tert-amylate, the high-yielding transfer of the difluorinated nucleophile takes place under high chemocontrol. Various sensitive functionalities (e.g. ester, nitrile, nitro, azido groups) can be accommodated across the isothiocyanate core, thus allowing a wide scope. The methodology is highly flexible and adaptable to prepare analogous α,α-difluoromethyl oxoamides by conveniently using isocyanates as the electrophilic building-blocks.

Direct and Chemoselective Synthesis of Tertiary Difluoroketones via Weinreb Amide Homologation with a CHF2-Carbene Equivalent

The homologation of Weinreb amides into difluoromethylketones with a formal nucleophilic CHF₂ transfer agent is reported. Activating TMSCHF₂ with potassium tert-amylate enables a convenient access to the difluorinated homologation reagent, which adds to the acylating partners. The high chemoselectivity showcased in the presence of variously multifunctionalized Weinreb amides, jointly with uniformly high yields, enables the strategy of general applicability without requiring any stabilization element for the putative carbanion.

A Unified Strategy for the Synthesis of Difluoromethyl- and Vinylfluoride-Containing Scaffolds

Here, we report a general method for the synthesis of quaternary and tertiary difluoromethylated compounds and their vinylfluoride analogues. The strategy, which relies on a two-step sequence featuring a C-selective electrophilic difluoromethylation and either a palladium-catalyzed decarboxylative protonation or a Krapcho decarboxylation, is practical, scalable, and high yielding. Considering the generality of the method and the attractive properties offered by the difluoromethyl group, this approach provides a valuable tool for late-stage functionalization and drug development.