Rhodium‐Catalyzed Defluorinative Vinylation of gem‐Difluoroalkenes for the Synthesis of 2‐Fluoro‐1,3‐dienes

Herein, we present a strategy for the formation of 2‐fluoro‐1,3‐diene derivatives via rhodium‐catalyzed direct C(sp²)—C(sp²) cross‐coupling of gem‐difluoroalkenes and acrylamides. By merging Rh(III)‐catalyzed C(sp²)–H bond activation and nucleophilic addition/F‐elimination of gem‐difluoroalkene, an efficient defluorinative vinylation reaction is uncovered, which leads to the generation of 2‐fluoro‐1,3‐dienes in moderate to good yields with excellent stereoselectivity under mild conditions. Preliminary mechanistic study suggests unique effects of fluorine substituents which allow the reactivity profile not observed with the congeners bearing heavier halides.     

Cleavage of Unactivated Si−C(sp3) Bonds with Reed's Carborane Acids: Formation of Known and Unknown Silylium Ions

An efficient method for the benzenium‐ion‐mediated cleavage of inert Si−C(sp³) bonds is reported. Various tetraalkylsilanes can thus be converted into the corresponding counteranion‐stabilized silylium ions. The reaction is chemoselective in the case of hexamethyldisilane. Computations reveal a mechanism with backside attack of the proton at one of the alkyl groups. Several activated Si−C(spⁿ) bonds (n=3–1) react equally well, and the procedure can be extended to the generation of stannylium ions.     

Synthesis and Reactivity of Paramagnetic Nickel Polypyridyl Complexes Relevant to C(sp2)–C(sp3)Coupling Reactions

A number of new transition metal catalyzed methods for the formation of C(sp²)–C(sp³) bonds have recently been described. These reactions often utilize bidentate polypyridyl‐ligated Ni catalysts, and paramagnetic Ni^I halide or aryl species are proposed in the catalytic cycles. However, there is little knowledge about complexes of this type. Here, we report the synthesis of paramagnetic bidentate polypyridyl‐ligated Ni halide and aryl complexes through elementary reactions proposed in catalytic cycles for C(sp²)–C(sp³) bond formation. We investigate the ability of these complexes to undergo organometallic reactions that are relevant to C(sp²)–C(sp³) coupling through stoichiometric studies and also explore their catalytic activity.     

Visible‐Light‐Driven Palladium‐Catalyzed Radical Alkylation of C−H Bonds with Unactivated Alkyl Bromides

Reported herein is a novel visible‐light photoredox system with Pd(PPh₃)₄ as the sole catalyst for the realization of the first direct cross‐coupling of C(sp³)−H bonds in N‐aryl tetrahydroisoquinolines with unactivated alkyl bromides. Moreover, intra‐ and intermolecular alkylations of heteroarenes were also developed under mild reaction conditions. A variety of tertiary, secondary, and primary alkyl bromides undergo reaction to generate C(sp³)−C(sp³) and C(sp²)−C(sp³) bonds in moderate to excellent yields. These redox‐neutral reactions feature broad substrate scope (>60 examples), good functional‐group tolerance, and facile generation of quaternary centers. Mechanistic studies indicate that the simple palladium complex acts as the visible‐light photocatalyst and radicals are involved in the process.     

Intramolecular Metal‐Free Oxidative Aryl–Aryl Coupling: An Unusual Hypervalent‐Iodine‐Mediated Rearrangement of 2‐Substituted N‐Phenylbenzamides

Hypervalent‐iodine‐mediated oxidative coupling of the two aryl groups in either 2‐acylamino‐N‐phenyl‐benzamides or 2‐hydroxy‐N‐phenylbenzamides, with concomitant insertion of the ortho‐substituted N or O atom into the tether, has been described for the first time. This unusual metal‐free rearrangement reaction involves an oxidative C(sp²)? C(sp²) aryl–aryl bond formation, cleavage of a C(sp²)? C(O) bond, and a lactamization/lactonization. Furthermore, unsymmetrical diaryl compounds can be easily obtained by removing the tether within the cyclized product.     

Direct oxidative C(sp3)─H/C(sp2)─H coupling reaction using recyclable Sr-doped LaCoO3 perovskite catalyst

A strontium-doped lanthanum cobaltite perovskite, La_0.6Sr_0.4CoO₃, was prepared and utilized as a recyclable heterogeneous catalyst for the direct oxidative C(sp³)─H/C(sp²)─H coupling reaction between cyclic ethers and alkenes or coumarins to achieve corresponding α-functionalized ethers. The α-functionalization of cyclic thioethers or amides with alkenes or coumarins was also achieved via this protocol. The La_0.6Sr_0.4CoO₃ catalyst exhibited better performance than a variety of homogeneous and heterogeneous catalysts. Utilizing a recyclable catalyst would offer a greener option for the direct oxidative C(sp³)─H/C(sp²)─H coupling reaction. To our best knowledge, the C(sp³)─H/C(sp²)─H coupling between olefins and ethers to generate α-functionalized ethers using a heterogeneous catalyst has not been previously reported, and the α-functionalization of cyclic thioethers or amides with alkenes or coumarins is new.     

Methylation of Arenols through Ni‐catalyzed C—O Activation with Methyl Magnesium Bromide

Direct alkylation of arenols with alkyl organometallic reagents has never been approached. Herein we reported the first successful example of nickel‐catalyzed methylation of arenols with methyl Grignard reagents to construct C(sp²)‐C(sp³) bond under mild conditions. The transformation was compatible with broad substrate scope of 2‐naphthol derivatives. Benzyl alcohol and biphenols were also suitable substrates for this methylation.     

Copper‐Catalyzed Three‐Component Carboazidation of Alkenes with Acetonitrile and Sodium Azide

A copper‐catalyzed three‐component reaction of alkenes, acetonitrile, and sodium azide afforded γ‐azido alkyl nitriles by formation of one C(sp³)−C(sp³) bond and one C(sp³)−N bond. The transformation allows concomitant introduction of two highly versatile groups (CN and N₃) across the double bond. A sequence involving the copper‐mediated generation of a cyanomethyl radical and its subsequent addition to an alkene, and a C(sp³)−N bond formation accounted for the reaction outcome. The resulting γ‐azido alkyl nitrile can be easily converted into 1,4‐diamines, γ‐amino nitriles, γ‐azido esters, and γ‐lactams of significant synthetic value.     

Visible Light Activation of Boronic Esters Enables Efficient Photoredox C(sp2)–C(sp3) Cross‐Couplings in Flow

We report herein a new method for the photoredox activation of boronic esters. Using these reagents, an efficient and high‐throughput continuous flow process was developed to perform a dual iridium‐ and nickel‐catalyzed C(sp²)–C(sp³) coupling by circumventing solubility issues associated with potassium trifluoroborate salts. Formation of an adduct with a pyridine‐derived Lewis base was found to be essential for the photoredox activation of the boronic esters. Based on these results we were able to develop a further simplified visible light mediated C(sp²)–C(sp³) coupling method using boronic esters and cyano heteroarenes under flow conditions.     

Application of Langlois' reagent（NaSO2CF3） in C–H functionalisation

The process of selectively introducing a CF₃ group into an organic molecule using inexpensive,stable,and solid sodium trifluoromethanesulfinate has rapidly advanced in recent years to become an eco-friendly method used by organic chemists to synthesize various natural and bioactive molecules.This review focuses on advances made within the last five years regarding C-H functionalisation,namely thermochemical C（sp²）-H（thio）trifluoromethylations,photochemical C（sp²）...     

Copper‐Mediated/Catalyzed Oxyalkylation of Alkenes with Alkylnitriles

A copper‐promoted oxyalkylation of alkenes with alkylnitriles has been developed. The protocol provides rapid access to phthalides (γ‐lactones) or isochromanones (δ‐lactones) via the formation of a C(sp³)?C(sp³) and a C(sp³)?O bond with the generation of up to two quaternary carbon atoms. Mechanistic studies suggest that this reaction is initiated by the formation of the C(sp³)?C(sp³) bond rather than the C(sp³)?O bond. Catalytic conditions were subsequently developed using carboxylic acid as an internal nucleophile.     

Iron-Catalyzed Cross-Coupling Reactions of Alkyl Grignards with Aryl Chlorobenzenesulfonates

Aryl sulfonate esters are versatile synthetic intermediates in organic chemistry as well as attractive architectures due to their bioactive properties. Herein, we report the synthesis of alkyl-substituted benzenesulfonate esters by iron-catalyzed C(sp²)–C(sp³) cross-coupling of Grignard reagents with aryl chlorides. The method operates using an environmentally benign and sustainable iron catalytic system, employing benign urea ligands. A broad range of chlorobenzenesulfonates as well as challenging alkyl organometallics containing β-hydrogens are compatible with these conditions, affording alkylated products in high to excellent yields. The study reveals that aryl sulfonate esters are the most reactive activating groups for iron-catalyzed alkylative C(sp²)–C(sp³) cross-coupling of aryl chlorides with Grignard reagents.     

Reactivity of (NNN)-pincer nickel(II) aryl complex towards oxidative carbon-heteroatom bond formation

The reactivity of an (NNN)-Ni(II) aryl complex towards C–X bond formation upon exposure to a panel of one- and two-electron oxidants is reported. High selectivity for C(sp²)–N bond formation is observed in all cases, except under conditions when C–C bond formation is accessible. Preliminary mechanistic investigations indicate access to either a Ni(III) or Ni(IV) intermediate dependent on oxidant used and that C–N bond formation is more efficient via Ni(IV) pathway due to geometry of reactive species.     

Pd(II)-catalyzed cascade Heck/intramolecular C(sp2)–H amidation reaction: An efficient route to 4-aryl-2-quinolinones

A Pd(II)-catalyzed cascade Heck/intramolecular C(sp²)–H amidation reaction is described for the synthesis of 4-aryl-2-quinolinone derivatives. Substituted cinnamamide containing 2-(pyridin-2-yl)ethanamine unit reacts with aryl iodide to form intermediate by Heck reaction. Then, the intermediate takes place intramolecular amidation via C(sp²)–H activated process promoted by orientation group.     

Rhodium(III)‐Catalyzed Cyclative Capture Approach to Diverse 1‐Aminoindoline Derivatives at Room Temperature

A Rh^III‐catalyzed C–H activation/cyclative capture approach, involving a nucleophilic addition of C(sp³)–Rh species to polarized double bonds is reported. This constitutes the first intermolecular catalytic method to directly access 1‐aminoindolines with a broad substituent scope under mild conditions.     

Photo‐promoted Skeletal Rearrangement of Phosphine–Borane Frustrated Lewis Pairs Involving Cleavage of Unstrained C−C σ‐Bonds

An unprecedented photo‐promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o‐(borylaryl)phosphines, involving cleavage of an unstrained sp²C–sp³C σ‐bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine–borane FLPs.     

Photo-promoted Skeletal Rearrangement of Phosphine–Borane Frustrated Lewis Pairs Involving Cleavage of Unstrained C−C σ-Bonds

An unprecedented photo-promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o-(borylaryl)phosphines, involving cleavage of an unstrained sp²C–sp³C σ-bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine–borane FLPs.     

Cross-coupling of 2-methylquinolines and in-situ activated isoquinolines: Construction of 1,2-disubstituted isoquinolinones

In this study, a method was developed to form C(sp³)–C(sp²) bonds via copper catalyst-promoted cross coupling of 2-methylquinoline and in-situ-activated 3-haloisoquinoline under mild conditions. The multi-component tandem reaction was used to construct new C–N, C=O and C–C bonds in one pot via sequential functionalization of the N1, C3 and C1 positions of 3-haloisoquinoline. This method can be used to efficiently access 1,2-disubstituted isoquinolinones by the three-component reaction of 3-halogen isoquinoline, alkyl halide, and 2-methylquinoline.     

Regio- and Diastereoselective Synthesis of Cyclohexadienylborons via an Intermolecular Diels–Alder Reaction of Alkenyl MIDA Boronates with 2-Pyrones

An efficient synthesis of highly functionalized cyclohexadienylborons via an inverse electron-demand Diels–Alder reaction/CO₂ extrusion of alkenyl MIDA boronates with 2-pyrones is outlined. By controlling the reaction temperature, the corresponding C(sp³)-rich bicyclolactones could also be readily formed. The exo-selective reactions feature good functional-group tolerance, broad substrate scope, and excellent regio- and diastereoselectivity. Oxidation of the cyclohexadienylborons in a one-pot procedure led to the construction of aromatic boronates bearing valuable functional groups. Synthetic transformations of the C−B bond were demonstrated.     

Transition-Metal-Free Coupling of Polyfluorinated Arenes and Functionalized,Masked Aryl Nucleophiles

A chemoselective C(sp²)−C(sp²) coupling of sufficiently electron-deficient fluorinated arenes and functionalized N-aryl-N’-silyldiazenes as masked aryl nucleophiles is reported. The fluoride-promoted transformation involves the in situ generation of the aryl nucleophile decorated with various sensitive functional groups followed by a stepwise nucleophilic aromatic substitution (S_NAr). These reactions typically proceed at room temperature within minutes. This catalytic process allows for the functionalization of both coupling partners, furnishing highly fluorinated biaryls in good yields.