Cobalt-Catalyzed Fluoroallyllation of Carbonyls via C-C Activation of gem-Difluorocyclopropanes

Palladium-Catalyzed Ring-Opening Defluorinative Hiyama Cross-Coupling of gem-Difluorocyclopropanes with Arylsilanes

We report an efficient palladium-catalyzed ring-opening defluorinative Hiyama cross-coupling of gem-difluorocyclopropanes with structurally diverse (hetero)arylsilanes through C-C bond activation and C-F bond cleavage. This regioselective ring-opening defluorinative Hiyama cross-coupling features a broad substrate scope with excellent functional group compatibility, affording a diverse variety of linear 2-fluoroallylic scaffolds in good yields with high Z-selectivity.

Palladium-catalyzed cross-coupling of gem-difluorocyclopropanes with gem-diborylalkanes: facile synthesis of a diverse array of gem-diboryl-substituted fluorinated alkenes

This study introduces an efficacious palladium-catalyzed method for the regioselective and stereoselective cross-coupling of gem-difluorinated cyclopropanes with an array of gem-diborylalkanes under mild reaction conditions. The innovative methodology facilitates the synthesis of 2-fluoroallylic gem-diboronic esters with exceptional Z-stereo- and chemo-selectivity. Notably, this protocol extended to the ligand-modulated regio- and stereoselectivity divergence cross-coupling of 1,1-difluoro-2-vinylcyclopropane as a reaction partner. Furthermore, we explore further transformations of the fluorinated gem-diboronates, encompassing the oxidation to form ketone and hydrogenation to generate mono-fluorinated alkylated gem-diboronate.

Pd-IPent-Catalyzed Defluorinative Annulation of gem-Difluorocyclopropanes with Enamides: Synthesis of Multisubstituted N-H Pyrroles

We present a Pd-IPent-catalyzed ring-opening defluorinative annulation reaction of gem-difluorocyclopropanes with enamides, which provides a convenient and efficient strategy for the synthesis of multisubstituted N-H pyrrole derivatives. This transformation selectively cleaves the C1-C3 bond, two C-F bonds, and the C-N bond in a one-pot procedure. Additionally, this protocol allows for the modification of several bioactive molecules.

Pd-IHept-Catalyzed Ring-Opening of gem-Difluorocyclopropanes with Malonates Via Selective C-C Bond Cleavage: Synthesis of Monofluoroalkenes

Monofluoroalkene scaffolds are frequently found in various functional molecules. Herein, we report a Pd-IHept-catalyzed (NHC = N-heterocyclic carbene) defluorinative functionalization approach for the synthesis of monofluoroalkenes from gem-difluorocyclopropanes and malonates. The flexible yet sterically hindered N,N'-bis(2,6-di(4-heptyl)phenyl)imidazol-2-ylidene ligand plays a key role in ensuring the high reaction efficiency. In addition, sterically hindered 1,1- and 1,2-disubstituted gem-difluorocyclopropanes could also be used in this transformation.

Palladium-Catalyzed Regioselective Monofluoroallylation of Indoles with gem-Difluorocyclopropanes

We present a palladium-catalyzed ring-opening reaction that induces indoles to cross-couple with gem-difluorocyclopropanes. The reaction proceeds through a domino process of C-C bond activation and C-F bond elimination, followed by C-C(sp2) coupling to produce various 2-fluoroallylindoles. This method is characterized by its high functional group tolerance, good yields and high regioselectivity, under base-free conditions. The synthetic utility of the products is illustrated by the functionalization of the NH and C2 positions of the indole scaffold.

Enantioselective Tsuji-Trost α-Fluoroallylation of Amino Acid Esters with Gem-Difluorinated Cyclopropanes

A novel enantioselective Tsuji-Trost-type cross coupling reaction between gem-difluorinated cyclopropanes and N-unprotected amino acid esters enabled by synergistic Pd/Ni/chiral aldehyde catalysis is presented herein. This transformation streamlined the diversity-oriented synthesis (DOS) of optically active α-quaternary α-amino acid esters bearing a linear 2-fluoroallylic motif, which served as an appealing platform for the construction of other valuable enantioenriched compounds. The key intermediates were confirmed by HRMS detection, while DFT calculations revealed that the excellent enantioselectivity was attributed to the stabilizing non-covalent interactions between the Pd(II)-π-fluoroallyl species and the Ni(II)-Schiff base complex.

Rhodium-Catalyzed Enantio- and Regioselective Allylation of Indoles with gem-Difluorinated Cyclopropanes

The use of gem-difluorinated cyclopropanes (gem-DFCPs) as fluoroallyl surrogates under transition-metal catalysis has drawn considerable attention recently but such reactions are restricted to producing achiral or racemic mono-fluoroalkenes. Herein, we report the first enantioselective allylation of indoles under rhodium catalysis with gem-DFCPs. This reaction shows exceptional branched regioselectivity towards rhodium catalysis with gem-DFCPs, which provides an efficient route to enantioenriched fluoroallylated indoles with wide substrate scope and good functional group tolerance.

High-Valent Copper Catalysis Enables Regioselective Fluoroarylation of Gem-Difluorinated Cyclopropanes

Transition-metal (TM) catalyzed reaction of gem-difluorinated cyclopropanes (gem-DFCPs) has drawn much attention recently. The reaction generally occurs via the activation of the distal C─C bond in gem-DFCPs by a low-valent TM through oxidative addition, eventually producing mono-fluoro olefins as the coupling products. However, achieving regioselective activation of the proximal C─C bond in gem-DFCPs that overcomes the intrinsic reactivity via TM catalysis remains elusive. Here, a new reaction mode of gem-DFCPs enabled by high-valent copper catalysis, which allows exclusive activation of the congested proximal C─C bond is presented. The reaction that achieves fluoroarylation of gem-DFCPs uses NFSI (N-fluorobenzenesulfonimide) as electrophilic fluoro reagent and arenes as the C─H nucleophiles, enabling the synthesis of diverse CF3-containing scaffolds. It is proposed that a high-valent copper species plays an important role in the regioselective activation of the proximal C─C bond possibly via a σ-bond metathesis.

Selectivity in Rh-catalysis with gem-difluorinated cyclopropanes

Small-ring chemistry is a fascinating field in organic chemistry. gem-Difluorinated cyclopropanes, a unique class of cyclopropanes, have garnered significant interest due to their intrinsic high reactivity. In this context, gem-difluorinated cyclopropanes have been extensively investigated as fluoroallylic synthons in Pd-catalyzed ring-opening/cross-coupling reactions for the synthesis of monofluoroalkenes with linear or branched selectivity. In contrast, Rh-catalysis has revealed diverse selectivity in the reaction of gem-difluorinated cyclopropanes, such as regioselectivity, enantioselectivity, and chemoselectivity. This feature article aims to summarize our efforts towards developing Rh-catalyzed reactions of gem-difluorinated cyclopropanes, briefly discussing the design, selectivity, reaction mechanisms and future research prospects.

Sn(OTf)2-Catalyzed (3 + 2) Cycloaddition/Sulfur Rearrangement Reaction of Donor-Acceptor Cyclopropanes with Indoline-2-thiones

The (3 + 2) cycloaddition/sulfur rearrangement reaction of donor-acceptor cyclopropanes bearing a single keto acceptor with indoline-2-thiones has been realized. Under the catalysis of Sn(OTf)2, a series of functionalized 3-indolyl-4,5-dihydrothiophenes were synthesized with moderate to excellent yields.

Pd/IPrBIDEA-Catalyzed Hydrodefluorination of gem-Difluorocyclopropanes: Regioselective Synthesis of Terminal Fluoroalkenes

Developing new strategies to enable chemo- and regioselective reductions is an important topic in chemical research. Herein, an efficient and regioselective Pd/IPrBIDEA-catalyzed ring-opening hydrodefluorination of gem-difluorocyclopropanes to access terminal fluoroalkenes is developed. The success of this transformation was attributed to the use of 3,3-dimethylallyl Bpin as a novel hydride donor. DFT calculations suggest that a direct 3,4'-hydride transfer via a 9-membered cyclic transition state is more favorable, which combined with the irreversibility of the reaction enables the unusual selectivity for the less thermodynamically stable terminal alkene isomer. This reaction mode is also applicable to a variety of regioselective allylic and propargyl reductions.

Palladium-Catalyzed Cross-Coupling of gem-Difluorocyclopropanes with gem-Diborylalkanes for the Synthesis of Boryl-Substituted Fluorinated Alkenes

This study presents a novel method for the regioselective coupling of gem-difluorinated cyclopropanes with gem-diborylmethane, utilizing a Pd-catalyst system. This innovative approach enables the synthesis of 2-fluoroalkenyl monoboronate scaffolds with high Z-selectivity. The resulting products undergo further transformations, including oxidation, Suzuki cross-coupling, and trifluoroborylation, all of which are achieved with good yields. This work introduces a valuable synthetic pathway to access important fluorinated compounds for various applications in organic chemistry.

Palladium-Catalyzed Fluorinative Bifunctionalization of Aziridines and Azetidines with gem-Difluorocyclopropanes

An unprecedented Pd-catalyzed fluorinative bifunctionalization of aziridines and azetidines was successfully developed via regioselective C-C and C-F bond cleavage of gem-difluorocyclopropanes, leading to various β,β'-bisfluorinated amines and β,γ-bisfluorinated amines. This reaction was achieved by incorporating a 2-fluorinated allyl group and a fluorine atom scissored from gem-difluorocyclopropane in 100 % atom economy for the first time. The mechanistic investigations indicated that the reaction underwent amine attacking 2-fluorinated allyl palladium complex to generate η2 -coordinated N-allyl aziridine followed by fluoride ligand transfer affording the final β- and γ-fluorinated amines.

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.

Synthesis of α-Difluoromethylene Ethers via Photoredox-Induced Hyperconjugative Ring Opening of gem-Difluorocyclopropanes

Fluorinated compounds have found widespread applications in pharmaceuticals, agrochemicals, and materials science. Precise construction of α-difluoromethylene ether (CF₂-O) moiety in organic molecules is of high demand. Herein, a visible light-promoted reaction protocol for the synthesis of α-difluoromethylene ether from gem-difluorocyclopropane is described. The key ring-opening step is induced by hyperconjugative interaction of cyclopropane with photo-oxidized aromatic rings. This reaction is easy scale-up, and the products bearing a synthetic handle enable their further manipulation.

Rh-catalyzed regio-switchable cross-coupling of gem-difluorinated cyclopropanes with allylboronates to structurally diverse fluorinated dienes

The control of linear/branched selectivity is one of the major focuses in transition-metal catalyzed allyl-allyl cross-coupling reactions, in which bond connection occurs at the terminal site of both the allyl fragments forming different types of 1,5-dienes. Herein, terminal/internal regioselectivity is investigated and found to be switchable in allyl-allyl cross-coupling reactions between gem-difluorinated cyclopropanes and allylboronates. The controlled terminal/internal regioselectivity arises from the fine-tuning of the rhodium catalytic system. Fluorinated 1,3-dienes, 1,4-dienes and 1,5-dienes are therefore produced in good yields with respectively isomerized terminal, internal, and terminal regioselectivity.

Enantioselective Formation of All-Carbon Quaternary Stereocenters in gem-Difluorinated Cyclopropanes via Rhodium-Catalyzed Stereoablative Kinetic Resolution

Herein, we report an effective method to offer chiral gem-difluorinated cyclopropanes containing an all-carbon quaternary stereocenter by rhodium-catalyzed stereoablative kinetic resolution. The activation of a sterically hindered all-carbon quaternary C-C bond through oxidative addition with a chiral rhodium complex is proposed as the enantiodetermining step. A wide range of gem-difluorinated cyclopropanes can be obtained with excellent ee values (ee = 87% to >99.9%), which are demonstrated to be useful chiral fluorine-containing building blocks by a series of postfunctionalizations.