Hydroarylation Of Alkenes Research Articles

Cobalt‐Catalyzed Hydroarylation of 2,3‐Dihydrofuran to Access α‐Arylated Tetrahydrofurans

AbstractThe α‐arylated tetrahydrofurans, commonly found in biologically active molecules, exhibit diverse biological activities and pharmacological effects. The functionalization of 2,3‐dihydrofuran offers a potential route for the synthesis of substituted tetrahydrofurans. Nevertheless, the development of earth‐abundant metal‐catalyzed regioselective hydrofunctionalization of 2,3‐dihydrofuran for the synthesis of substituted tetrahydrofurans remains to be pursued. Herein, we report a cobalt‐catalyzed hydroarylation of 2,3‐dihydrofuran, which serves as the first example of cobalt hydride‐catalyzed alkene hydroarylation. This reaction provides an efficient method for the synthesis of α‐arylated tetrahydrofurans with high reaction efficiency, exclusive α‐arylation selectivity, and remarkable functional group compatibility.

Sulfoximine Aided Ru(II)-Catalyzed Asymmetric Double C(sp2)-H Hydroarylations of Olefins.

Presented here is a sulfoximine-directed Ru(II)-catalyzed asymmetric intramolecular double C(sp2)-H hydroarylation of olefins. This process provides a diastereoselective and enantiospecific synthetic route to highly substituted tetrahydrobenzodifurans. Notably, the reaction accommodates labile functional groups and is scalable to gram quantities.

Study of Palladium-Catalyzed Site and Regioselective Reductive Heck Hydroarylation of Unactivated Alkene.

We studied the reaction pathway of our reductive Heck hydroarylation using a palladium catalyst and a hydrosilane. A key question to verify the reaction mechanism was which active species, Ar-PdII-I or Si-PdII-H, first performs migratory insertion into the alkenes. Identifying this step is crucial to elucidate the reaction mechanism. To address this, we designed a substrate containing two trisubstituted alkenes and tested its product. The results suggest that the migratory insertion of Ar-PdII-I into the alkene is the initial step of the reaction. Furthermore, this reaction can construct a quaternary carbon center and give high yields with high functional group tolerance.

Iron(III) Triflate and γ-Cyclodextrin-Catalyzed Hydroarylation of Alkenes with 1-Naphthols and 2-Naphthols

AbstractA Fe(OTf)3 and γ-cyclodextrin-catalyzed hydroarylation of alkenes with 1-naphthols or 2-naphthols is demonstrated. This efficient and general method delivers a wide range of benzylic naphthols from readily available starting materials with high chemo- and regioselectivity in up to 99% yield, with no need for a strong base or additive.

Iridium-Catalyzed Asymmetric Hydroarylation of Unactivated Alkenes with Heterobiaryls: Simultaneous Construction of Axial and Central Chirality.

There are only a few examples being reported for the simultaneous control of central chirality and axial chirality because it is more challenging. Herein, we report an iridium-catalyzed asymmetric hydroarylation of unactivated alkenes with heterobiaryls to simultaneously construct axial and central chirality. The reaction showed a broad substrate scope and delivered the products with satisfactory results. The results of the control experiments demonstrated that the FerroLANE ligand promotes the reaction to proceed along a specific modified Chalk-Harrod mechanism.

Photoinduced Intermolecular Radical Hydroalkylation of Olefins via Ligated Boryl Radicals-Mediated Halogen Atom Transfer.

Light-mediated Halogen-Atom Transfer (XAT) has become a significant methodology in contemporary synthesis. Unlike α-aminoalkyl and silyl radicals, ligated boryl radicals (LBRs) have not been extensively explored as halogen atom abstractors. In this study, we introduce NHC-ligated boranes as optimal radical chain carriers for the intermolecular reductive radical hydroalkylation and hydroarylation of electron-deficient olefins by using direct UV-A light irradiation. DFT analysis allowed us to rationalize the critical role of the NHC ligand in facilitating efficient chain propagation.

Transition-metal-catalyst-free electroreductive alkene hydroarylation with aryl halides under visible-light irradiation.

The radical hydroarylation of alkenes is an efficient strategy for accessing linear alkylarenes with high regioselectivity. Herein, we report the electroreductive hydroarylation of electron-deficient alkenes and styrene derivatives using (hetero)aryl halides under mild reaction conditions. Notably, the present hydroarylation proceeded with high efficiency under transition-metal-catalyst-free conditions. The key to success is the use of 1,3-dicyanobenzene as a redox mediator and visible-light irradiation, which effectively suppresses the formation of simple reduction, i.e., hydrodehalogenation, products to afford the desired products in good to high yields. Mechanistic investigations proposed that a reductive radical-polar crossover pathway is likely to be involved in this transformation.

Photocatalytic alkenes to ring-fused quinazolin-4(3H)-ones via proton-transfer shuttle using TFA

Herein, a novel metal-free photocatalytic system is reported that enables intramolecular hydroarylation of unactivated alkenes via a proton transfer shuttle using TFA, providing a concise access to the formation of pyrroloquinazolinone and pyridyquinazolinone products in moderate to good yields. Mechanistic studies revealed that the protonated quinazolinone is the key radical precursor mediating the intramolecular cyclization reaction.

The Resorcinarene Hexameric Capsule as a Supramolecular Photoacid to Trigger Olefin Hydroarylation in Confined Space.

The self-assembled resorcinarene capsule C6 shows remarkable photoacidity upon light irradiation, which is here exploited to catalyze olefin hydroarylation reactions in confined space. An experimental pKa* value range of -3.3--2.8 was estimated for the photo-excited hexameric capsule C6 *, and consequently an increase in acidity of 8.8 log units was observed with respect to its ground state (pKa=5.5-6.0). This makes the hexameric capsule the first example of a self-assembled supramolecular photoacid. The photoacid C6 * can catalyze hydroarylation reaction of olefins with aromatic substrates inside its cavity, while no reaction occurred between them in the absence of irradiation and/or capsule. DFT calculations corroborated a mechanism in which the photoacidity of C6 * plays a crucial role in the protonation step of the aromatic substrate. A further proton transfer to olefin with a concomitant C-C bond formation and a final deprotonation step lead to product releasing.

Transition-Metal-Free Anti-Markovnikov Hydroarylation of Alkenes with Aryl Chlorides through Consecutive Photoinduced Electron Transfer.

The hydroarylation of alkenes has emerged as a powerful strategy for arene functionalization. However, aryl chlorides remain a large challenge in this type of reaction due to the chemical inertness of the C(sp2)-Cl bond and high negative reduction potential. Herein, we report an anti-Markovnikov radical hydroarylation of alkenes with aryl chlorides via visible-light photoredox catalysis. The key reactive aryl radicals can be efficiently achieved from aryl chlorides by consecutive photoinduced electron transfer. This transition-metal-free protocol features mild conditions, a wide substrate scope, and functional group tolerance, producing a diverse range of linear alkylarenes in moderate to good yields. The reaction is proposed to proceed through a radical-polar crossover pathway.

Palladium-Catalyzed Reductive Heck Hydroarylation of Unactivated Alkenes Using Hydrosilane at Room Temperature.

The reductive Heck hydroarylation of unactivated alkenes has emerged as an essential reaction for regioselective hydroarylation. Herein, we report a palladium-catalyzed reductive Heck hydroarylation of unactivated alkenes under mild conditions with enhanced functional group tolerance using hydrosilane as the reducing reagent. Under the optimal conditions, the alkylarene yields increased, resulting in minimal undesired products. Mechanistic studies using deuterated reagents indicated the involvement of two competing catalytic cycles.

Photoinduced Co/Ni-cocatalyzed Markovnikov hydroarylation of unactivated olefins with aryl bromides.

Transition-metal-catalyzed hydroarylation of unactivated alkenes via metal hydride hydrogen atom transfer (MHAT) is an attractive approach for the construction of C(sp2)-C(sp3) bonds. However, this kind of reaction focuses mainly on using reductive hydrosilane as a hydrogen donor. Here, a novel photoinduced Co/Ni-cocatalyzed Markovnikov hydroarylation of unactivated alkenes with aryl bromides using protons as a hydrogen source has been developed. This reaction represents the first example of photoinduced MHAT via a reductive route intercepting an organometallic coreactant. The key to this transformation was that the CoIII-H species was generated from the protonation of the CoI intermediate, and the formed CoIII-C(sp3) intermediate interacted with the organometallic coreactant rather than reacting with nucleophiles, a method which has been well developed in photoinduced Co-catalyzed MHAT reactions. This reaction is characterized by its high catalytic efficiency, construction of quaternary carbons, simple reaction conditions and expansion of the reactive mode of Co-catalyzed MHAT reactions via a reductive route. Moreover, this catalytic system could also be applied to complex substrates derived from glycosides.

Visible light-induced ruthenium(ii)-catalyzed hydroarylation of unactivated olefins.

Hydroarylation reactions have emerged as a valuable tool for the direct functionalization of C-H bonds with ideal atom economy. However, common catalytic variants for these transformations largely require harsh reaction conditions, which often translate into reduced selectivites. In contrast, we herein report on a photo-induced hydroarylation of unactivated olefins at room temperature employing a readily available ruthenium(ii) catalyst. Our findings include high position- and regio-selectivity and remarkable tolerance of a wide range of functional groups, which further enabled the late-stage diversification.

Mechanistic insight into Ni(i)-catalyzed regioselective alkene hydroarylation: is it carbonickelation or hydronickelation?

DFT calculations reveal a hydronickelation rather than carbonickelation mechanism for the Ni(i)-catalyzed alkene hydroarylation, demonstrating strong theoretical–experimental synergy.

Asymmetric Nickel-Catalyzed Hydroarylation and Dicarbofunctionalization of Unactivated Alkenes

Asymmetric Nickel-Catalyzed Hydroarylation and Dicarbofunctionalization of Unactivated Alkenes

Highly selective α-C(sp3)-H arylation of alkenyl amides via nickel chain-walking catalysis

Herein, we report the migratory hydroarylation of unactivated alkenes with aryl iodides using native and weakly coordinating amide directors under mild conditions. Synergistic coordination of the monodentate directing group and the ligand enable the highly regioselective migratory hydroarylation via a chain walking process to form the thermodynamically stable five-membered nickelacyle intermediate. The protocol provides a variety of valuable α-aryl-substituted alkylamine products, and exhibited good functional group tolerance. The modification of bioactive compounds such as fenofibrate and indomethacin further highlights the synthetic value of this protocol.

Divergent Photosensitizer Controlled Reactions of 4‐Hydroxycoumarins and Unactivated Olefins: Hydroarylation and Subsequent [2+2] Cycloaddition

AbstractHerein, we report a photoinduced approach for hydroarylation of unactivated olefins using 4‐hydroxycoumarins as the arylating reagent. Key to the success of this reaction is the conversion of nucleophilic 4‐hydroxycoumarins into electrophilic carbon radicals via photocatalytic arene oxidation, which not only circumvents the polarity‐mismatch issue encountered under ionic conditions but also accommodates a broad substrate scope and inhibits side reactions that were previously observed. Moreover, divergent reactivity was achieved by changing the photocatalyst, enabling a subsequent [2+2] cycloaddition to deliver cyclobutane‐fused pentacyclic products that are otherwise challenging to access in high yields and with high diastereoselectivity. Mechanistic studies have elucidated the mechanism of the reactions and the origin of the divergent reactivity.

Divergent Photosensitizer Controlled Reactions of 4-Hydroxycoumarins and Unactivated Olefins: Hydroarylation and Subsequent [2 + 2] Cycloaddition.

Herein, we report a photoinduced approach for hydroarylation of unactivated olefins using 4-hydroxycoumarins as the arylating reagent. Key to the success of this reaction is the conversion of nucleophilic 4-hydroxycoumarins into electrophilic carbon radicals via photocatalytic arene oxidation, which not only circumvents the polarity-mismatch issue encountered under ionic conditions but also accommodates a broad substrate scope and inhibits side reactions that were previously observed. Moreover, divergent reactivity was achieved by changing the photocatalyst, enabling a subsequent [2+2] cycloaddition to deliver cyclobutane-fused pentacyclic products that are otherwise challenging to access in high yields and with high diastereoselectivity. Mechanistic studies have elucidated the mechanism of the reactions and the origin of the divergent reactivity.

Mo-catalyzed Friedel-Crafts alkylation using alkenes under mild condition

Mo-catalyzed hydroarylation of alkenes can be achieved at room temperature. The procedure can perform by using electron rich arenes, and the corresponding product is obtained regioselectively as a mixture of para- and ortho-isomers in good yield. Both aryl alkenes and aliphatic alkenes are available in the procedure. On the other hand, a reaction of allylic acetates gives the corresponding allyl arenes via leaving of acetoxy group.

Iridium‐Catalyzed Remote Site‐Switchable Hydroarylation of Alkenes Controlled by Ligands

AbstractAn iridium‐catalyzed remote site‐switchable hydroarylation of alkenes was reported, delivering the products functionalized at the subterminal methylene and terminal methyl positions on an alkyl chain controlled by two different ligands, respectively, in good yields and with good to excellent site‐selectivities. The catalytic system showed good functional group tolerance and a broad substrate scope, including unactivated and activated alkenes. More importantly, the regioconvergent transformations of mixtures of isomeric alkenes were also successfully realized. The results of the mechanistic studies demonstrate that the reaction undergoes a chain‐walking process to give an [Ar−Ir−H] complex of terminal alkene. The subsequent processes proceed through the modified Chalk–Harrod‐type mechanism via the migratory insertion of terminal alkene into the Ir−C bond followed by C−H reductive elimination to afford the hydrofunctionalization products site‐selectively.