Stereoselective cobalt-catalyzed halofluoroalkylation of alkynes

Cobalt-Catalyzed Cross-Coupling of Glycosyl Sulfones with Zinc reagents toward the Stereoselective Synthesis of C(sp/sp2)-Glycosides

A cobalt-catalyzed desulfonylative cross-coupling of glycosyl sulfones with organozinc reagents toward the stereoselective synthesis of C-glycosides is reported. The new C-glycoside synthesis proceeds under mild reaction conditions and exhibits tolerance to a range of functional groups. Diverse alkynylated, arylated, and alkenylated products are formed with high efficiency and excellent diastereoselectivity. Mechanistic studies indicate a radical pathway.

Asymmetric Cobalt Catalysis for the Construction of Quaternary Stereogenic Centers with Fluorine Atoms

The advancement of robust synthetic methodologies for generating fluorinated quaternary carbon chiral centers is highly sought after in the fields of organic and medicinal chemistry. This study successfully provides such compounds through cobalt-catalyzed asymmetric Negishi coupling reactions of α-bromo-α-fluoro ketones with aryl/alkenyl zinc reagents. The adjustment of chiral unsymmetric N,N,N-tridentate (CUT) ligands played a key role in improving reactivity and selectivity in the cobalt catalysis, preventing the formation of hydrodebromination byproducts, and accommodating sterically hindered substrates and heterocycles. Control and kinetic experiments reveal that transmetalation serves as the rate-limiting step, a mechanistic characteristic that sets the newly developed asymmetric cobalt-catalyzed cross-couplings apart from previous methodologies.

Photoinduced Iron-Catalyzed Decarboxylation/Isomerization of gem-Difluoroallyl Carboxylic Acid to Access Vinyl Difluoromethylene Units

Vinyl difluoromethylene units (-CF-) significantly enhance the bioactivity and physical and chemical properties of compounds. Despite recent advances in introducing vinyl difluoromethylene units, radical-mediated formation of these motifs remains largely unexplored. A novel serial catalytic strategy for selective defluoroalkylation of trifluoromethyl alkenes has been developed, utilizing photocatalytic defluorocarboxylation followed by photoinduced iron-catalyzed decarboxylation/isomerization. The defluoroalkylation reaction involves generating difluoroallyl radicals, tautomerizing to vinyl difluoromethylene radicals, and proceeding through radical addition and alkylation.

Cobalt-Catalyzed Enantioselective Reductive Coupling of Imines and Internal Alkynes

Chiral allylamines are important structural components in natural products, pharmaceuticals, and chiral catalysts. Herein, we report a cobalt-catalyzed enantioselective reductive coupling of imines with internal alkynes to synthesize chiral allylamines. The reaction is catalyzed by a cobalt complex derived from commercially available bisphosphine ligand utilizing zinc as the electron donor. The substrate scope is extensive. Symmetric and unsymmetric alkyl and aryl alkynes have been successfully coupled with various imines derived from aryl and alkyl aldehydes. Tri- and tetra-substituted allyl amines were isolated in high yields, with enantiomeric excess surpassing >99.9 % and regioselectivities exceeding >20 : 1. These chiral allyl amines can serve as versatile platforms for subsequent transformations while preserving their stereochemical integrity. Extensive experimental and computational mechanistic studies were performed to elucidate the mechanism. These investigations have indicated that an in situ cobalt(I) catalyst enables the oxidative cyclization of alkynes and imines, and a spin crossover occurs during the enantio-determining step. Zinc plays a pivotal role in facilitating the transmetallation of the resulting azacobaltacycle. The observed enantioselectivity was interpreted by the stabilization of the transition state through higher stabilizing interaction energy from high negative polarization, dispersion, and C-H⋅⋅⋅π interactions.

New reactivity of late 3d transition metal complexes in catalytic reactions of alkynes

Late 3d metals such as iron, cobalt, nickel, and copper are abundantly present in the Earth's crust and they are produced in huge quantities in the mining industry. Often, these inexpensive metals exhibit unique or special reactivities in catalytic reactions as compared with expensive noble metals such as palladium, iridium, and rhodium. The novel reactivities of 3d metal complexes originate from their unique physical and atomic properties as compared with heavier 4d/5d congeners: smaller ionic and covalent radii, contracted 3d orbitals of smaller sizes and lower energies, lower values of Pauli electronegativity, etc. This review summarizes the recent progress in late 3d transition metal-catalyzed transformations of alkynes. We organize catalytic examples according to each type of novel elementary reactivity exhibited by 3d metal complexes. Each section includes a description of the unique reactivity of the 3d metals, the atomic and theoretical basis of the reactivity and illustrations of catalytic examples: (1) single electron transfer from low-valent metal complexes to alkyl halides, (2) facile reductive elimination from nickel(III), (3) facile reductive elimination from copper(III), (4) cis-to-trans isomerization of alkenyl metal complexes after syn-insertion, (5) ligand-to-ligand hydrogen transfer, (6) hydrogen atom transfer from hydride complexes and (7) protonation of nickel metallacyclopropenes.

Cobalt-catalyzed reductive cross-coupling: a review

Transition-metal-catalyzed reductive cross-coupling is highly efficient for forming C-C bonds. It earns its limelight from its application by coupling unreactive electrophilic substrates to synthesize a variety of carbon-carbon bonds with various hybridizations (sp, sp2, and sp3), late-stage functionalization, and bioactive molecules' synthesis. Reductive cross-coupling is challenging to bring selectivity but promising approach. Cobalt is comparatively more affordable than other highly efficient metals e.g., palladium and nickel but cobalt catalysis is still facing efficacy challenges. Researchers are trying to harness the maximum out of cobalt's catalytic properties. Shortly, with efficiency achieved combined with the affordability of cobalt, it will revolutionize industrial applications. This review gives insight into the core of cobalt-catalyzed reductive cross-coupling reactions with a variety of substrates forming a range of differently hybridized coupled products.

Oxy-difluoroallylation of Ynamides by Nickel-Catalyzed Tandem Alkoxylation/Claisen Rearrangement

A nickel-catalyzed tandem alkoxylation/claisen rearrangement strategy for the oxy-difluoroallylation of ynamides has been developed. In this reaction, 3,3-difluoroallyl alcohol was used as a fluorine-containing building block to construct the C-CF2 bond for the first time. This approach is recognized for its robust tolerance of functional groups, impressive yields, and excellent atomic efficiency, all achieved under mild reaction conditions. A series of β,β-difluoromethyleneamide derivatives were efficiently obtained through simple operations, and their practicality was confirmed through gram-scale synthesis and product derivatization.

A metal-free strategy to construct fluoroalkyl-olefin linkages using fluoroalkanes

We present a metal-free strategy to access fluoroalkyl-olefin linkages from fluoroalkane precursors and vinyl-pinacol boronic ester (BPin) reagents. This reaction sequence is templated by the boron reagent, which induces C-C bond formation upon oxidation. We developed this strategy into a one-pot synthetic protocol using RCF2H precursors directly with vinyl-BPin reagents in the presence of a Brønsted base, which tolerated oxygen- and nitrogen-containing heterocycles, and aryl halogens. We also found that HCF3 (HCF-23; a byproduct of the Teflon industry) and CH2F2 (HCF-32; a low-cost refrigerant) are amenable to this protocol, representing distinct strategies to generate RCF2H and RCF3 molecules. Finally, we demonstrate that the vinyldifluoromethylene products can be readily derivatized, representing an avenue for late-stage modification after installing the fluoroalkyl unit.

Cobalt-Catalyzed Enantioconvergent Negishi Cross-Coupling of α-Bromoketones

Cobalt-catalyzed enantioconvergent cross-coupling of α-bromoketones with aryl zinc reagents is achieved to access chiral ketones bearing α-tertiary stereogenic centers with high enantioselectivities. The more challenging and sterically hindered α-bromoketones bearing a 2-fluorophenyl group or β-secondary and tertiary alkyl chains could also be well-tolerated. Adjusting the electronic effect of chiral unsymmetric N,N,N-tridentate ligands is critical for improving the reactivity and selectivity of this transformation, which is beneficial for further studies of asymmetric 3d metal catalysis via ligand modification. The control experiments and kinetic studies illustrated that the reaction involved radical intermediates and the reductive elimination was a rate-determining step.

Cobalt-Catalyzed Decarboxylative Allylations: Development and Mechanistic Studies

In recent years, there has been a concerted drive to develop methods that are greener and more sustainable. Being an earth-abundant transition metal, cobalt offers an attractive substitute for commonly employed precious metal catalysts, though reactions engaging cobalt are still less developed. Herein, we report a method to achieve the decarboxylative allylation of nitrophenyl alkanes, nitroalkanes, and ketones employing cobalt. The reaction allows for the formation of various substituted allylated products in moderate-excellent yields with a broad scope. Additionally, the synthetic potential of the methodology is demonstrated by the transformation of products into versatile heterocyclic motifs. Mechanistic studies revealed an in situ activation of the Co(II)/dppBz precatalyst by the carboxylate salt to generate a Co(I)-species, which is presumed to be the active catalyst.

Dual Photoredox/Nickel-Catalyzed Dehydrative Difluoroalkylation of Benzyl Alcohols for the Synthesis of Allylic gem-Difluorides

A photoredox/Lewis acid cooperative catalytic system has been developed for the construction of Cvinyl-CRf bonds through the dehydrative difluoroalkylation of benzyl alcohols. A variety of allylic gem-difluorides could be obtained in moderate yields with good to excellent E/Z selectivity. In addition, several control experiments have been explored, and a possible mechanism was proposed for this process.

Synthesis of Chiral Tertiary Allylic- and Propargylic Fluorides from Nonaflates of Chiral α-Fluorinated β-Keto Dicarbonyl Compounds

The acetyl group of chiral α-fluorinated dicarbonyl compounds was transformed to nonaflates through a reaction with perfluorobutanesulfonyl fluoride in the presence of DBU in 82-95% yield. These nonaflates were used in Suzuki and Sonogashira coupling reactions to afford chiral tertiary allylic fluorides bearing gem-disubstituted terminal alkenes with excellent optical purities (45-91%, ≥94% ee). In addition, chiral tertiary propargylic fluorides were obtained from the reaction of nonaflates with DBU (73-86%, ≥94% ee).

Visible-Light-Induced Radical gem-Iodoallylation of 2,2,2-Trifluorodiazoethane

A visible-light-induced radical gem-iodoallylation of CF₃CHN₂ was developed under mild conditions, delivering a variety of α-CF₃-substituted homoallylic iodide compounds in moderate to excellent yields. The transformation features broad substrate scope, good functional group compatibility, and operational simplicity. The described protocol provides a convenient and attractive tool to apply CF₃CHN₂ as CF₃-introduction reagent in radical synthetic chemistry.

Iodine-Mediated Coupling of 2,2,2-Trifluorodiazoethane and Alkynes To Access Bistrifluoromethylated 1,3,5-Trienes

Multi-component reaction of higher degree ultilization of diazo molecules for polyene formation is highly intriuging but still underexplored. We present herein an unprecedented coupling of 2,2,2-trifluorodiazoethane and aryl alkynes mediated by iodine under visible light. The multi-component reaction involving two diazo units and two alkyne units provides a straightforward and step-economic access to bistrifluoromethylated 1,3,5-trienes in high stereoselectivity by creation of three C═C bonds in a single step under mild conditions.

Transition-metal-free Synthesis of tetra-substituted Vinyl Iodides by Cascade Sequential Reaction of α-Keto Acids, 1-Iodoalkynes, and Alkyl Halides

The cascade sequential reaction of α-keto acids, 1-iodoalkynes, and alkyl halides are reported herein to synthesize tetra-substituted vinyl iodides. It represents an efficient protocol to access a diverse range of tetra-substituted vinyl iodides starting from simple materials in a one-pot fashion, featuring mild reaction conditions, ease of operation, and broad substrate scope.

Co-Catalyzed atom transfer radical addition of bromodifluoroacetamides, expanding the scope of radical difluoroalkylation

The atom transfer radical addition (ATRA) of bromodifluoroacetamides to arylalkynes and terminal alkenes was conducted using von Wangelin's Co catalyst system (CoBr₂/1,2-bis(diphenylphosphino)benzene/Zn) in acetone/H₂O at 30 °C to afford the corresponding functionalized difluoroacetamides in 33-89% yields. Moreover, the Co catalyst was successfully applied to the tandem addition/cyclization of 1,6-diene and -enyne substrates and intramolecular ATRA of N-allyl and N-propargyl bromodifluoroacetamides, significantly expanding the scope of radical difluoroalkylation.

Iodoperfluoroalkylation of unactivated alkenes via pyridine-boryl radical initiated atom-transfer radical addition

The pyridine/bis(pinacolate)diboron combination has been found to be able to initiate the iodoperfluoroalkylation of unactivated alkenes with perfluoroalkyl iodides. Theoretical calculations and control experiments indicate that the atom transfer radical addition mechanism is responsible for the formation of iodoperfluoroalkylation products. This metal-free and photo-free strategy is applicable to a wide range of perfluoroalkyl iodides and unactivated alkenes with good functional group tolerance. Further applications in iodoperfluoroalkylation of organic semiconductor-relevant or bioactive molecules demonstrate the synthetic potential of this method.

A diastereoselective synthesis of cyclopentanones via photocatalytic reductive alkyltrifluoromethylation of ynones

A photocatalytic reductive alkyltrifluoromethylation of ynones with the Langlois reagent is developed, providing a regio- and diastereoselective access to trifluoromethylated cyclopentanones under mild conditions.

HFIP-Catalyzed Difluoroalkylation of Propargylic Alcohols to Access Tetrasubstituted Difluoroalkyl Allenes

A hexafluoroisopropanol (HFIP)-catalyzed difluoroalkylation of propargylic alcohols with difluoroenoxysilanes to access structurally diverse tetrasubstituted difluoroalkyl allenes has been developed. This convenient procedure enables the rapid construction of highly functionalized multisubstituted fluorinated allenes in a mild and straightforward way. Furthermore, the synthetic potential of this methodology has been demonstrated by the facile synthesis of various structurally interesting fluorine-containing molecules such as gem-difluorosubstituted dihydropyran, tetrasubstituted CF₂H-allene, and multisubstituted fluorinated cyclopentanone derivatives.

Organozinc pivalates for cobalt-catalyzed difluoroalkylarylation of alkenes

Installation of fluorine into pharmaceutically relevant molecules plays a vital role in their properties of biology or medicinal chemistry. Direct difunctionalization of alkenes and 1,3-dienes to achieve fluorinated compounds through transition-metal catalysis is challenging, due to the facile β-H elimination from the Csp³‒[M] intermediate. Here we report a cobalt-catalyzed regioselective difluoroalkylarylation of both activated and unactivated alkenes with solid arylzinc pivalates and difluoroalkyl bromides through a cascade Csp³‒Csp³/Csp³‒Csp² bond formation under mild reaction conditions. Indeed, a wide range of functional groups on difluoroalkyl bromides, olefins, 1,3-dienes as well as (hetero)arylzinc pivalates are well tolerated by the cobalt-catalyst, thus furnishing three-component coupling products in good yields and with high regio- and diastereoselectivity. Kinetic experiments comparing arylzinc pivalates and conventional arylzinc halides highlight the unique reactivity of these organozinc pivalates. Mechanistic studies strongly support that the reaction involves direct halogen atom abstraction via single electron transfer to difluoroalkyl bromides from the in situ formed cobalt(I) species, thus realizing a Co(I)/Co(II)/Co(III) catalytic cycle.

Synthesis and Photochemical Application of Hydrofluoroolefin (HFO) Based Fluoroalkyl Building Block

A novel fluoroalkyl iodide was synthesized on multigram scale from refrigerant gas HFO-1234yf as cheap industrial starting material in a simple, solvent-free, and easily scalable process. We demonstrated its applicability in a metal-free photocatalytic ATRA reaction to synthesize valuable fluoroalkylated vinyl iodides and proved the straightforward transformability of the products in cross-coupling chemistry to obtain conjugated systems.

Chemoselective Hydro(Chloro)pentafluorosulfanylation of Diazo Compounds with Pentafluorosulfanyl Chloride

Pentafluorosulfanyl chloride (SF₅ Cl) is the most prevalent reagent for the incorporation of SF₅ group into organic compounds. However, the preparation of SF₅ Cl often relies on hazardous reagents and specialized apparatus. Herein, we described a safe and practical synthesis of a bench-stable and easy-to-handle solution of SF₅ Cl in n-hexane under gas-reagent-free conditions. The synthetic application of SF₅ Cl was demonstrated through the unprecedented reaction with diazo compounds. The chemoselective hydro- and chloropentafluorosulfanylations of α-diazo carbonyl compounds were developed in the presence of K₃ PO₄ or copper catalyst, respectively. These reactions provide a direct and efficient access to various α-pentafluorosulfanyl carbonyl compounds of high value for potential applications.

3,3-Difluoroallyl ammonium salts: highly versatile, stable and selective gem-difluoroallylation reagents

The selective synthesis of fluorinated organic molecules continues to be of major importance for the development of bioactive compounds (agrochemicals and pharmaceuticals) as well as unique materials. Among the established synthetic toolbox for incorporation of fluorine-containing units, efficient and general reagents for introducing -CF2- groups have been largely neglected. Here, we present the synthesis of 3,3-difluoropropen-1-yl ammonium salts (DFPAs) as stable, and scalable gem-difluoromethylation reagents, which allow for the direct reaction with a wide range of fascinating nucleophiles. DFPAs smoothly react with N-, O-, S-, Se-, and C-nucleophiles under mild conditions without necessity of metal catalysts with exclusive regioselectivity. In this way, the presented reagents also permit the straightforward preparation of many analogues of existing pharmaceuticals.

Diethylzinc-Mediated Radical 1,2-Addition of Alkenes and Alkynes

A novel diethylzinc-mediated radical 1,2-addition of perfluoroalkyl iodides to unactivated alkenes and alkynes is presented, which demonstrates a novel way to generate an ethyl difluoroacetate radical. This method is highly efficient and gives full conversions of the substrates, high yields of the products, and negligible byproducts and requires no column chromatography purifications. The mild conditions enable this protocol to exhibit excellent functional group compatibility.

Halotrifluoromethylation of 1,3-Enynes: Access to Tetrasubstituted Allenes

A highly regioselective copper-catalyzed 1,4-chloro- and bromotrifluoromethylation of 1,3-enynes has been presented for the first time, which affords an efficient transformation to access halo- and CF₃-containing tetrasubstituted allene derivatives with good to excellent yield. This protocol is practical and convenient, in which a wide range of functional groups are compatible. Applications of this method for the gram-scale preparation and late-stage functionalization of biologically active molecules are also demonstrated.

Radical 1,2-addition of bromoarenes to alkynes via dual photoredox and nickel catalysis

A 1,2-addition of aryl bromides to alkynes enabled by the photocatalytic generation of bromine radicals via photoredox and nickel catalysis is reported.

Cu-Catalyzed radical-triggered spirotricyclization of enediynes and enyne-nitriles for the synthesis of pentacyclic spiroindenes

A new copper-catalyzed radical-triggered fluoromethylation-spirotricyclization of enediyne- and enyne-nitrile-containing para-quinone methides (p-QMs) was reported for the first time, and used to produce a series of hitherto unreported pentacyclic spiroindenes.

Stereoselective synthesis of fluoroalkylated (Z)-alkene via nickel-catalyzed and iron-mediated hydrofluoroalkylation of alkynes

An efficient nickel-catalyzed, iron-mediated hydrofluoroalkylation of alkynes with bromodifluoroacetate or perfluoroalkyl iodide, which proceeded smoothly to give fluoroalkylated (Z)-alkenes with high stereocontrol (up to 99 : 1 Z/E), was developed.

Photoinitiated stereoselective direct C(sp2)–H perfluoroalkylation and difluoroacetylation of enamides

Photoinitiated regio- and stereoselective C(sp²)–H perfluoroalkylation and difluoroacetylation of enamides are developed, furnishing biologically and physiologically privileged fluoro-containing enamide scaffolds.

Visible light photocatalytic cross-coupling and addition reactions of arylalkynes with perfluoroalkyl iodides

Visible light photocatalytic cross-coupling and addition reactions of arylalkynes with perfluoroalkyl iodides have been developed. Through slight modifications of the reaction conditions, reactions that are selective for the preparation of the C-C coupling product (perfluoroalkyl alkynes) and the addition products (iodo-perfluoroalkyl substituted alkenes) can be achieved. These reactions work well with different types of alkynes and perfluoroalkyl iodides. As the iodide generated from the reaction can serve as a reductant to regenerate the photocatalyst from its oxidized form, no sacrificial electron donor is required.

Metal-Catalyzed Spiroannulation-Fluoromethylfunctionaliztions of 1,5-Enynes for the Synthesis of Stereodefined (Z)-Spiroindenes

Two classes of new catalytic spiroannulation-fluormethylfunctionaliztions of para-quinone methide (p-QM)-containing 1,5-enynes have been established under redox-neutral conditions. Palladium-catalyzed spiroannulation-iododifluoromethylation with ethyl difluoroiodoacetate oriented completely stereoselective access to (Z)-spiroindenes and the latter included copper-catalyzed three-component spiroannulation-cyanotrifluoromethylation starting from Togni's reagent and trimethylsilanecarbonitrile (TMSCN). Both reaction pathways involve fluoroalkyl radical-triggered 1,6-addition/5-exo-dig annulation/metal radical cross-coupling/reductive elimination sequence, providing practical and stereoselective protocols for rapidly constructing cyclohexadienone-containing spiroindenes with generally good yields.

AIBN-Induced Remote Trifluoromethyl-Alkynylation of Thioalkynes

A novel α,α'-azobis(isobutyronitrile) (AIBN)-induced remote trifluoromethyl-alkynylation of thioalkynes with alkynyl triflones as both the trifluoromethyl and alkyne sources is described. Structurally diverse trifluoromethylated (Z)-enynes can be constructed with full control of regio-, stereo-, and site-selectivity, which serves as a highly selective method for the rapid construction of trifluoromethylated molecules.

Visible-light Promoted Atom Transfer Radical Addition-Elimination (ATRE) Reaction for the Synthesis of Fluoroalkylated Alkenes Using DMA as Electron-Donor

Here, we describe a mild, catalyst-free and operationally-simple strategy for the direct fluoroalkylation of olefins driven by the photochemical activity of an electron donor−acceptor (EDA) complex between DMA and fluoroalkyl iodides. The significant advantages of this photochemical transformation are high efficiency, excellent functional group tolerance, and synthetic simplicity, thus providing a facile route for further application in pharmaceuticals and life sciences.