Catalytic Enantioselective Boryl and Silyl Substitution with Trifluoromethyl Alkenes: Scope, Utility, and Mechanistic Nuances of Cu–F β-Elimination

Copper-catalyzed highly switchable defluoroborylation and hydrodefluorination of 1-(trifluoromethyl)alkynes

CF2-containing compounds hold significant potential in drug discovery, organic synthesis, and materials science. However, synthesizing various CF2-containing building blocks from a single compound remains challenging. Here, we present a Cu-catalyzed, switchable defluoroborylation and hydrodefluorination of trifluoromethylated alkynes, yielding four types of CF2-containing compounds. The chemo- and regio-selective sp2/sp3 1,2-diborylation and sp2 monoborylation of 1-(trifluoromethyl)alkynes are controlled by adjusting the solvent and ligand quantity. Additionally, altering the base allows selective generation of gem-difluoroalkenes or difluoromethylalkenes. Notably, our method prevents over-defluorination of the CF3 group on unsaturated C-C bonds during nucleophilic additions, preserving the pharmaceutically valuable CF2 group. Experimental data and density functional theory (DFT) calculations elucidate the regioselectivities of Cu-Bpin addition and the regulatory role of the ligand in selective deborylation processes.

Synthesis of Z-gem-Cl,CF3-Substituted Alkenes by Stereoselective Cross-Metathesis and the Role of Disubstituted Mo Alkylidenes

Stereochemically defined organofluorine compounds are central to drug discovery and development. Here, we present a catalytic cross-metathesis method for the synthesis of Z-trisubstituted olefins that contain a Cl- and a CF3-bound carbon terminus. Notably, the process is stereoselective, which is in contrast to the existing stereoretentive strategies that also involve a trisubstituted olefin as starting material. Reactions are catalyzed by a Mo monoaryloxide pyrrolide alkylidene, involve a trisubstituted alkene and gem-Cl,CF3-substituted alkene, and are fully Z-selective. Catalytic cross-coupling can be used to convert the C-Cl bond of the trisubstituted olefin to C-B, C-D, and different C-C bonds. We elucidate the role of Cl,CF3-disubstituted Mo alkylidenes. Experimental and computational (DFT) data show that in some instances a disubstituted alkylidene is formed and then transformed to a more active complex. In other cases, the Cl,CF3-disubstituted alkylidene is a direct participant in a catalytic cycle. The studies described shed new light on the chemistry of high oxidation-state disubstituted alkylidenes-scarcely investigated entities likely to be pivotal to approaches for stereocontrolled synthesis of tetrasubstituted alkenes through olefin metathesis.

Photocatalytic Synthesis of γ,γ-Difluoroallylic Ketones and δ,δ-Difluoroallylic Ketones via a Desulfurative/Defluorinative Alkylation Process

The gem-difluoroalkene moiety is frequently found in medicinal chemistry. From α-keton sulfides and thioic acids, we were able to develop a universal approach for the synthesis of γ,γ-difluoroallylic ketones and δ,δ-difluoroallylic ketones via a desulfurative/defluorinative alkylation process. We expect that this mild and efficient method will be complementary to other known strategies.

Cu-Catalyzed Regioselective Silylation of Chloro-Substituted Allenyl-Bdan

A copper-catalyzed efficient regioselective silylation reaction of chloro-substituted allenyl-Bdan was developed. Under mild reaction conditions, allenyl and propargyl silane compounds can be selectively obtained in moderate to high yields by adjusting the bases and solvents used in the reactions. This study offers direct and efficient methods for synthesizing multifunctionalized allenyl and propargyl silane compounds from the same initial material of chloro-substituted allenyl-Bdan.

Catalytic Regio- and Enantioselective Boracarboxylation of Arylalkenes with CO2 and Diboron

Catalytic asymmetric carboxylation of readily available alkenes with CO2, an abundant and sustainable one-carbon building block, that gives access to value-added α-stereogenic carboxylic acids in an atom- and step-economic manner is highly attractive. However, it has remained a formidable challenge for the synthetic community. Here, the first example of Cu-catalyzed highly regio- and enantioselective boracarboxylation reaction on various arylalkenes with diboron under an atmospheric pressure of CO2 is described, which afforded a variety of chiral β-boron-functionalized α-aryl carboxylic acids with up to 87% yield and 97% ee under mild conditions. Importantly, α-substituted arylalkenes could also be subject to this protocol with excellent enantiopurities, thereby rendering an efficient approach for the generation of enantioenriched carboxylic acids with an α-chiral all-carbon quaternary center. Moreover, high functional group tolerance, scalable synthesis, and facile access to bioactive compounds, like (-)-scopolamine, (-)-anisodamine, and (-)-tropicamide, further demonstrated the synthetic utility of this strategy.

Synthetic Advantages of Defluorinative C-F Bond Functionalization

Much progress has been made in the development of methods to both create compounds that contain C-F bonds and to functionalize C-F bonds. As such, C-F bonds are becoming common and versatile synthetic functional handles. This review summarizes the advantages of defluorinative functionalization reactions for small molecule synthesis. The coverage is organized by the type of carbon framework the fluorine is attached to for mono- and polyfluorinated motifs. The main challenges, opportunities and advances of defluorinative functionalization are discussed for each class of organofluorine. Most of the text focuses on case studies that illustrate how defluorofunctionalization can improve routes to synthetic targets or how the properties of C-F bonds enable unique mechanisms and reactions. The broader goal is to showcase the opportunities for incorporating and exploiting C-F bonds in the design of synthetic routes, improvement of specific reactions and advent of new methods.

Copper-Catalyzed Regio- and Enantioselective Hydroboration of Difluoroalkyl-Substituted Internal Alkenes

Catalytic asymmetric hydroboration of fluoroalkyl-substituted alkenes is a straightforward approach to access chiral small molecules possessing both fluorine and boron atoms. However, enantioselective hydroboration of fluoroalkyl-substituted alkenes without fluorine elimination has been a long-standing challenge in this field. Herein, a copper-catalyzed hydroboration of difluoroalkyl-substituted internal alkenes with high levels of regio- and enantioselectivities is reported. The native carbonyl directing group, copper hydride system, and bisphosphine ligand play crucial roles in suppressing the undesired fluoride elimination. This atom-economic protocol provides a practical synthetic platform to obtain a wide scope of enantioenriched secondary boronates bearing the difluoromethylene moieties under mild conditions. Synthetic applications including functionalization of biorelevant molecules, versatile functional group interconversions, and preparation of difluoroalkylated Terfenadine derivative are also demonstrated.

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.

Catalytic σ-Bond Annulation with Ambiphilic Organohalides Enabled by β-X Elimination

We describe a catalytic cascade sequence involving directed C(sp3 )-H activation followed by β-heteroatom elimination to generate a PdII (π-alkene) intermediate that then undergoes redox-neutral annulation with an ambiphilic aryl halide to access 5- and 6-membered (hetero)cycles. Various alkyl C(sp3 )-oxygen, nitrogen, and sulfur bonds can be selectively activated, and the annulation proceeds with high diastereoselectivity. The method enables modification of amino acids with good retention of enantiomeric excess, as well as σ-bond ring-opening/ring-closing transfiguration of low-strain heterocycles. Despite its mechanistic complexity, the method employs simple conditions and is operationally straightforward to perform.

Stereospecific Nickel-Catalyzed Cross-Electrophile Coupling Reaction of Alkyl Mesylates and Allylic Difluorides to Access Enantioenriched Vinyl Fluoride-Substituted Cyclopropanes

Cross-electrophile coupling reactions involving direct C-O bond activation of unactivated alkyl sulfonates or C-F bond activation of allylic gem-difluorides remain challenging. Herein, we report a nickel-catalyzed cross-electrophile coupling reaction between alkyl mesylates and allylic gem-difluorides to synthesize enantioenriched vinyl fluoride-substituted cyclopropane products. These complex products are interesting building blocks with applications in medicinal chemistry. Density functional theory (DFT) calculations demonstrate that there are two competing pathways for this reaction, both of which initiate by coordination of the electron-deficient olefin to the low-valent nickel catalyst. Subsequently, the reaction can proceed by oxidative addition of the C-F bond of the allylic gem-difluoride moiety or by directed polar oxidative addition of the alkyl mesylate C-O bond.

Photo/Ni dual-catalyzed radical defluorinative sulfonylation to synthesize gem-difluoro allylsulfones

Radical defluorinative functionalization of α-trifluoromethyl styrenes represents an effective way toward gem-difluoroalkenes. There are general interests in developing novel synthetic protocols for defluorinative functionalization with various types of radicals. However, reports on the preparation of gem-difluoro allylsulfones via an S-centered radical pathway are limited. Herein, we developed a photo/nickel dual-catalyzed defluorinative sulfonylation that rapidly and reliably synthesizes gem-difluoro allylsulfones. The merit of this protocol is exhibited by its mild conditions and wide scope, thus providing a novel strategy for the sulfonyl radical participating in radical defluorinative coupling.

Copper-catalyzed defluorinative arylboration of vinylarenes with polyfluoroarenes

An unprecedented but challenging defluorinative arylboration has been achieved. Enabled by a copper catalyst, an interesting procedure on defluorinative arylboration of styrenes has been established. With polyfluoroarenes as the substrates, this methodology offers flexible and facile access to provide a diverse assortment of products under mild reaction conditions. In addition, by using a chiral phosphine ligand, an enantioselective defluorinative arylboration was also realized, affording a set of chiral products with unprecedented levels of enantioselectivity.

Cu-catalyzed cascade difluoroalkylation/5-endo cyclization/β-fluorine cleavage of ynones

A copper-catalyzed, redox-neutral cascade difluoroalkylation/5-endo annulation/β-fluorine cleavage of ynones is developed, providing a direct and stereoselective method to access synthetically important α-monofluoroalkenyl cyclopentanones. Mechanistic studies suggest an unprecedented Cu^II-assisted β-fluorine fragmentation, which may be valuable for the challenging but important C-F bond activation. Moreover, the in situ generated difluorocarbene was found to serve as an effective reductant for the regeneration of copper(I) catalyst, thus avoiding the addition of external reductants.

Theoretical Insight into the Multiple Roles of LiHMDS in Pd-Catalyzed Borylation of Fluorobenzene

Pd-catalyzed borylation of fluorobenzene was theoretically studied. DFT calculations revealed that the reaction occurs through an unprecedented 3 + 6-membered ring transition state, in which one LiHMDS (HMDS = hexamethyldisilazane) acts as a ligand and another LiHMDS is essential to provide Li···N and Li···F interactions, overcoming the large destabilization of the strong phenyl-F bond distortion. The characteristic feature of LiHMDS was elucidated by comparing it with HMDS and NaHMDS analogues.

Diastereo- and enantioselective synthesis of compounds with a trifluoromethyl- and fluoro-substituted carbon centre

Molecules that contain one or more fluorine atoms are crucial to drug discovery. There are protocols available for the selective synthesis of different organofluorine compounds, including those with a fluoro-substituted or a trifluoromethyl-substituted stereogenic carbon centre. However, approaches for synthesizing compounds with a trifluoromethyl- and fluoro-substituent stereogenic carbon centre are far less common. This potentially impactful set of molecules thus remains severely underdeveloped. Here we introduce a catalytic regio-, diastereo- and enantioselective strategy for the preparation of homoallylic alcohols bearing a stereogenic carbon centre bound to a trifluoromethyl group and a fluorine atom. The process, which involves a polyfluoroallyl boronate and is catalysed by an in situ-formed organozinc complex, can be used for diastereodivergent preparation of tetrafluoro-monosaccharides, including ribose core analogues of the antiviral drug sofosbuvir (Sovaldi). Unexpected reactivity/selectivity profiles, probably originating from the trifluoromethyl- and fluoro-substituted carbon site, are discovered, foreshadowing other unique chemistries that remain unknown.

Divergent Synthesis of Fluorinated Alkenes, Allenes, and Enynes via Reaction of 2-Trifluoromethyl-1,3-enynes with Carbon Nucleophiles

Herein, inorganic base K₃PO₄ promoted divergent synthesis of CF₃-substituted allenes, cyclopentenes, alkynes, and fluorinated enynes via regioselective nucleophilic addition of carbon nucleophiles to 2-trifluoromethyl-1,3-enynes was developed. With the choice of different carbon nucleophiles, various fluorinated compounds could be obtained under K₃PO₄/DMF reaction system. When malononitriles were used as nucleophiles, CF₃-substituted allenes, cyclopentenes, and alkynes could be obtained, respectively. By using 1,3-dicarbonyl compounds as nucleophiles, ring-monofluorinated 4H-pyrans could be prepared, and 1,1-difluoro-1,3-enynes could be furnished with the participation of diethyl malonate. Moreover, these five kinds of fluorinated allenes, alkenes, and enynes are valuable building blocks.

Nickel-catalyzed enantioselective α-heteroarylation of ketones via C-F bond activation to construct all-carbon quaternary stereocenters

Nickel-catalyzed asymmetric α-heteroarylation of ketones with fluorinated heteroarenes is reported via C-F bond activation. A series of ketones and 2-fluoropyridine derivatives with different functional groups proceed well to provide the corresponding products containing all-carbon quaternary stereocenters in good yields (up to 99% yield) and high ee values (up to 99% ee). In addition, drug molecule donepezil could also be compatible under the reaction conditions to afford late-stage diversification of pharmaceuticals.

Cu-Catalyzed Switchable Asymmetric Defluoroalkylation and [3 + 2] Cycloaddition of Trifluoropropene

Chiral fluorinated amino esters and pyrrolidines are privileged scaffolds in synthetic chemistry and exhibit unique biological properties. We report the facile preparation of these compounds through copper-catalyzed switchable defluoroalkylation and [3 + 2] cycloaddition of trifluoropropene in an asymmetric fashion. The choice of solvent and chiral ligand was crucial for the efficient transformation and exquisite chemoselectivity pattern from identical starting materials that rapidly and reliably incorporate gem-difluoroalkene and trifluoromethyl (CF₃) motifs to generate a diverse range of enantioenriched fluorinated building blocks in good to excellent yields with high asymmetric induction.

Enantioselective nickel-catalyzed dicarbofunctionalization of 3,3,3-trifluoropropene

Despite paramount applications of chiral trifluoromethylated compounds in medicinal chemistry and materials science, limited strategies have been developed for catalytic asymmetric synthesis of such valuable fluorinated structures. Here, we report a nickel catalyzed enantioselective dicarbofunctionalization of inexpensive industrial chemical 3,3,3-trifluoropropene (TFP) with readily available tertiary alkyl and aryl iodides. The reaction overcomes the β-F elimination side reaction of TFP, and proceeds efficiently under mild reaction conditions. The protocol possesses advantages, such as synthetic convenience, high enantioselectivity, and excellent functional group tolerance, providing rapid and straightforward access to chiral trifluoromethylated compounds of medicinal interest.

Strategies for the catalytic asymmetric synthesis of trifluoromethylated compounds remain scarce. Here, the authors report the nickel-catalyzed enantioselective dicarbofunctionalization of 3,3,3-trifluoropropene.

Enantioselective Copper-Catalyzed sp2/sp3 Diborylation of 1-Chloro-1-Trifluoromethylalkenes

Fluorine-containing organoboron compounds have emerged as novel building blocks in chemical synthesis; among them, fluorinated sp²/sp³ diborylated compounds are particularly appealing, since they might undergo chemoselective and diversified transformations of different C-B bonds with fluorinated functionality, thus bringing versatility and complexity to the eventual products. However, expedient, synthetic strategies for the construction of such fluorinated diborylative compounds are very sparse. Herein, we disclose enantioselective Cu-catalyzed sp²/sp³ diborylations of 1-chloro-1-trifluoromethylalkenes, leading to diborylated compounds bearing a gem-difluoroalkenyl moiety; most intriguingly, the new formed C-B bonds include one stereoselective and optically pure Csp³-B bond. Further transformations on the eventual products demonstrated the values of our presented strategy.

Rhodium(I)-Catalyzed Defluorinative Coupling of Boronic Acids with Monofluoroalkenes

We herein describe a highly selective Rh(I)-catalyzed defluorinative coupling of boronic acids with (E)-β-monofluoroacrylates. In contrast to previous methods, the trisubstituted (Z)-alkene products were obtained in excellent dr with an inversion of double bond geometry. Experimental and computational studies established that Rh(I)-facilitated β-F elimination is favored over competing β-H elimination and protodemetalation.

Photoredox Metal-Free Allylic Defluorinative Silylation of α-Trifluoromethylstyrenes with Hydrosilanes

We report an efficient strategy that combines organic photoredox and hydrogen atom transfer to deliver gem-difluoroallylsilanes via defluorinative silylation of α-trifluoromethylstyrenes using hydrosilanes as silicon sources. This protocol provides an environmentally friendly approach for the preparation of structurally diverse gem-difluoroallylsilanes with excellent functional group compatibility and renders it suitable for late-stage modification of bioactive and complex molecules.

Catalytic Asymmetric Construction of CF3-Substituted Chiral sp3 Carbon Centers

Due to the unique steric and electronic nature of the fluorine atom, organofluorine compounds have received significant attention in the fields of pharmaceuticals and agrochemicals. In particular, the CF3 group is frequently found in biologically active compounds. However, compared to aryl- and alkenyl-CF3-containing molecules, the construction of sp3 carbon-based alkyl-CF3-containing molecules, particularly via catalytic enantioselective synthesis, remains a considerable challenge in spite of their high potential in medicinal applications. This short review focuses on recent advances in this research area, and the reported strategies are categorized according to reaction types and starting substrates. In addition, chiral catalysts, substrate scope, and reaction mechanisms are briefly summarized.

1 Introduction

2 Stereoselective Introduction of a CF3 Group

2.1 Nucleophilic Addition to Carbonyls and Imines

2.2 Electrophilic Substitution at the α Position of Carbonyls

2.3 Allylic Nucleophilic Substitution

3 Stereoselective Functionalization of CF3-Substituted Molecules

3.1 Electrophilic Substitution of α-CF3 Carbonyls

3.2 Substitution of α-Halo CF3 Compounds

3.3 Addition-Type Reactions with CF3-Substituted Alkenes

4 Conclusion and Outlook

Catalytic Asymmetric β‐Oxygen Elimination**

A catalytic enantioselective β‐O‐elimination reaction is reported in the form of a zirconium‐catalyzed asymmetric opening of meso‐ketene acetals. Furthermore, a regiodivergent β‐O‐elimination is demonstrated. The reaction proceeds under mild conditions, at low catalyst loadings, and produces chiral monoprotected cis‐1,2‐diols in good yield and enantiomeric excess. The combination with a Mitsunobu reaction or a one‐pot hydroboration/Suzuki reaction sequence then gives access to additional diol and aminoalcohol building blocks. A stereochemical analysis supported by DFT calculations reveals that a high selectivity in the hydrozirconation step is also important for achieving high enantioselectivity, although it does not constitute the asymmetric step. This insight is crucial for the future development of related asymmetric β‐elimination reactions.

Regio- and Stereoselective Addition to gem-Difluorinated Ene-Ynamides: Access to Stereodefined Fluorinated Dienes

The first synthesis of gem-difluorinated ene-ynamides is presented via deprotonation of trifluoromethylated N-allenamides and δ extrusion of fluorine. These highly reactive building blocks, owing to their dual functional groups, offer a unique entry to difluorinated dienes and to stereodefined, monofluoro-substituted dienes. Stereoselective addition to the ynamide moiety led to difluorinated dienes. A stereocontrolled domino δ elimination reaction followed by an addition/elimination sequence from trifluoromethylated N-allenamides provided exclusively stereodefined monofluorinated ene-ynamides.

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

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

Synthesis of Allenyl-Bdan via Cu(I)-Catalyzed Borylation of Propargyl gem-Dichlorides

A copper-catalyzed borylation of propargyl dichlorides was developed under mild reaction conditions. The corresponding chloro-substituted allenyl-Bdan products were obtained in good yields. The utilities of allenyl-Bdan products were examined by their diverse derivatizations.

Copper-Catalyzed Ring-Opening Defluoroborylation of gem-Difluorinated Cyclobutenes: A General Route to Bifunctional 1,3-Dienes and Their Applications

The exploration of the reactivity of gem-difluorinated small-size rings has continuously drawn attention in recent years but is limited to three-membered carbocycles. Herein we report a copper-catalyzed reaction of gem-fluorinated cyclobutenes with bis(pinacolato)diboron (B₂pin₂). A sequence of defluoroborylation and a ring-opening process produces B,F-bifunctional 1,3-dienes in a stereoselective manner. The transformation together with the efficient downstream coupling of the boronate and the fluoride moieties collectively constitutes a modular route to highly functionalized and stereocontrolled 1,3-dienes.

Recent Advances in the Construction of Fluorinated Organoboron Compounds

Fluorinated organoboron compounds are important synthetic building blocks that combine the unique characteristics of a fluorinated motif with the versatile synthetic applications of organoboron moiety. This review article guides the research on fluorinated organoboron compounds mainly from four aspects in recent years: selective monodefluoroborylation of polyfluoroarenes and polyfluoroalkenes, selective borylation of fluorinated substrates, selective fluorination of organoboron compounds, and borofluorination of alkynes/olefins. In addition, this review will provide a necessary guidance and inspiration for the research on the valuable synthetic building block fluorinated organoboron compounds.

Nickel-Catalyzed Stereo- and Enantioselective Cross-Coupling of gem-Difluoroalkenes with Carbon Electrophiles by C-F Bond Activation

Stereo- and enantioselective cross-electrophile coupling involving C-F bond activation is reported. Treatment of gem-difluoroalkenes with racemic benzyl electrophiles in the presence of a chiral nickel complex using B₂ pin₂ as a stoichiometric reductant allows the construction of a C(sp² )-C(sp³ ) bond under mild conditions, affording a broad range of monofluoroalkenes bearing stereogenic allylic centers. Initial mechanistic studies indicate that a radical chain pathway may be operating, wherein the ester group in the gem-difluoroalkene promotes C-F bond activation through oxidative addition to a Ni species.

gem-Difluoroallylation of Aryl Halides and Pseudo Halides with Difluoroallylboron Reagents in High Regioselectivity

We report the palladium-catalyzed gem-difluoroallylation of aryl halides and pseudo halides with 3,3-difluoroallyl boronates in high yield with high regioselectivity, and we report the preparation of the 3,3-difluoroallyl boronate reactants by a copper-catalyzed defluorinative borylation of inexpensive gaseous 3,3,3-trifluoropropene with bis(pinacolato)diboron. The gem-difluoroallylation of aryl and heteroaryl bromides proceeds with low catalyst loading (0.1 mol % [Pd]) and tolerates a wide range of functional groups, including primary alcohols, secondary amines, ethers, ketones, esters, amides, aldehydes, nitriles, halides, and nitro groups. This protocol extends to aryl iodides, chlorides, and triflates, as well as substituted difluoroallyl boronates, providing a versatile synthesis of gem-difluoroallyl arenes that we show to be valuable intermediates to a series of fluorinated building blocks.

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.

Copper-Catalyzed Highly Selective Protoboration of CF3 -Containing 1,3-Dienes

The copper-catalyzed highly selective protoboration of CF₃ -containing conjugated diene with proton source and B₂ Pin₂ has been developed. This chemistry could suppress the well-known defluorination and provide borated reagents with an intact CF₃ -group. Further studies indicated that the functional group tolerance of this chemistry is very well, and the products could be used as versatile precursors for different types of transformations. Importantly, using chiral diphosphine ligand, we have developed the first example for using such starting material to synthesis allylic boron-reagents which bearing a CF₃ -containing chiral center. Notably, the reaction mechanism was intensively studied by DFT calculations, which could reveal the reason that defluorination was inhibited.

Selective C-F Bond Allylation of Trifluoromethylalkenes

Selective C-F bond functionalization of CF₃ group represents an appealing strategy for the incorporation of pharmaceutically privileged difluoromethylene moiety. Despite the recent significant advancement attained in the functionalization of Ar-CF₃ molecules, prescriptions amenable for alkenyl-CF₃ congeners remain sufficiently inadequate. Herein, we report a strategically novel protocol for the C-F bond elaboration of trifluoromethylalkene derivatives. By using readily available allyl metallics as nucleophilic coupling partner, the present reaction enables an expedient construction of structurally diversified CF₂ -bridged 1,5-dienes. Furthermore, the exquisite selectivity observed in this transformation is revealed to be based on the underlying mechanism that consists of a cascade of nucleophilic S_N 2' defluorinative allylation and electronically promoted Cope rearrangement.