Aryl Alkenes Research Articles

Electrochemical Azidocyanation of Alkenes

AbstractThe difunctionalization of alkenes—a process that installs two functional groups in a single operation and transforms chemical feedstocks into value‐added products—is one of the most appealing synthetic methods in contemporary chemistry. However, the introduction of two distinct functional groups via two readily accessible nucleophiles remains a formidable challenge. Existing intermolecular alkene azidocyanation methods, which primarily focus on aryl alkenes and rely on stoichiometric chemical oxidants. We report herein an unprecedented electrochemical strategy for alkene azidocyanation that is compatible with both alkyl and aryl alkenes. This is achieved by harnessing the finely‐tuned anodic electron transfer and the strategic selection of copper/ligand complexes. The reactions of aryl alkenes were rendered enantioselective by employing a chiral ligand. Crucially, the mild conditions and well‐regulated electrochemical process assure exceptional tolerance for various functional groups and substrate compatibility with both terminal and internal alkyl alkenes.

Cp2ZrCl2-catalyzed synthesis of aryl substituted tertiary alcohols by the reaction of aryl olefins with ketones under the action of AlCl3 and Mg

An efficient one-step method for the synthesis of aryl substituted tertiary alcohols based on the reaction of aryl olefins with ketones under the action of AlCl3 and Mg in the presence of catalytic amounts of Cp2ZrCl2 was developed.

Synergistic silver-mediated and palladium-catalyzed nondirected olefination of aryl C–H bond: quick access to multi-substituted aryl olefins

Synergistic silver-mediated and palladium-catalyzed nondirected olefination of aryl C–H bond: quick access to multi-substituted aryl olefins

Synthesis of Carbonyl Compounds from Carboxylic Acids, Alkenes, and Aryl Alkanes by mpg-Carbon Nitride

Synthesis of Carbonyl Compounds from Carboxylic Acids, Alkenes, and Aryl Alkanes by mpg-Carbon Nitride

Organocatalytic Asymmetric Vinylogous Michael Addition of Electron-Deficient Aryl Alkane Nucleophiles to Enals.

We report herein a protocol for an organocatalyzed asymmetric vinylogous Michael addition of aryl alkane nucleophiles with enals under base- and additive-free conditions. A series of allylic building blocks were obtained in 60%-93% yield and 88-99% ee with 20 mol % diphenylprolinol silyl ether as catalyst. This protocol has advantages such as excellent chemoselectivity and regioselectivity, good tolerance of functionalities, and simple reaction conditions.

Substituent-Determined Intramolecular Hydrogen Transfer for Photopromoted Intermolecular Cycloaddition of Anthraquinones with Aryl Olefins.

The formation of intramolecular hydrogen bonds in anthraquinones makes them inert to photoinduced reactions; therefore, it is a great challenge to phototransform these compounds. Herein, we reported a formal visible-light-induced [4 + 2] cycloaddition of both 1-hydroxyanthraquinones and 1-aminoanthraquinones with olefins under external photocatalyst-free conditions with high regioselectivity. More than 60 substrates are disclosed, demonstrating the reliability of this protocol to construct diverse functionalized anthraquinone derivatives.

Regioselectivity Inversion in Hydroformylation of Aryl Alkenes with a Diphosphoramidite-rhodium Catalyst

Abstract: Rhodium catalysts for hydroformylation of aryl alkenes generally promote the formation of branched aldehydes. Here, we have demonstrated that by using a single rhodium catalyst containing a diphosphoramidite ligand derived from BINOL, it is possible to achieve the inversion of regioselectivity in the hydroformylation of aryl alkenes simply by reducing the syngas pressure or, alternatively, increasing the reaction temperature. Indeed, the hydroformylation of styrene carried out at 20 bar and 50°C resulted in 72% of 2- phenylpropanal, while at atmospheric pressure, 71% of 3-phenylpropanal was obtained. A similar linear selectivity (72-74%) was observed when the hydroformylation of styrene, pmethylstyrene, and p-methoxystyrene was performed at 10 bar and higher temperature (80°C). The regioselectivity of the hydroformylation of trans-β-methylstyrene under mild conditions (80°C, 10-20 bar) was also strongly influenced by the syngas pressure. The results of this study show that it is possible to reverse the selectivity of aryl alkenes hydroformylation with a single catalyst by simply exploring the reaction conditions. In this paper, we have shown that the inversion of the regioselectivity in the hydroformylation of aryl alkenes can be achieved using a single rhodium catalyst containing a BINOL-derived diphosphoramidite ligand by reducing the syngas pressure or, alternatively, increasing the reaction temperature.

Enantiodivergent Functionalization of Aryl Alkenes into Diverse Biarylalkanoic Acids by Integrating Biocatalytic Cascades with Chemocatalysis

Enantiodivergent Functionalization of Aryl Alkenes into Diverse Biarylalkanoic Acids by Integrating Biocatalytic Cascades with Chemocatalysis

Cu‐Catalyzed Site‐ and Enantioselective Borylcyanation of 1,2‐Disubstituted Aryl Alkenes

AbstractA catalytic chemo‐ and enantioselective generation of secondary benzylic copper complexes from Cu−B(pin) (pin=pinacolato) additions to 1,2‐disubstituted aryl alkenes followed by in situ site selective cyanation at either aryl group or benzylic position to construct multifunctional alkylboron compounds is presented. The method is distinguished by identification of chiral Cu complexes leading to not only high enantioselectivity but also better efficiency compared with achiral catalysts. In addition, an unprecedented mode of cyanation at benzylic site through dearomative isomerization was disclosed. Functionalization of multifunctional alkylboron products provides useful building blocks that are otherwise difficult to access.

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.

Photoelectrochemical Asymmetric Catalysis Enables Enantioselective Heteroarylcyanation of Alkenes via C-H Functionalization.

The asymmetric difunctionalization of alkenes, a method transforming readily accessible alkenes into enantioenriched chiral structures of high value, has long been a focal point of organic synthesis. Despite tremendous efforts in this domain, it remains a considerable challenge to devise enantioselective oxidative dicarbofunctionalization of alkenes, even though these transformations can utilize stable and unfunctionalized functional group donors. In this context, we report herein a photoelectrocatalytic method for the enantioselective heteroarylcyanation of aryl alkenes, which employs unfunctionalized heteroarenes through C-H functionalization. The photoelectrochemical asymmetric catalysis (PEAC) method combines photoredox catalysis and asymmetric electrocatalysis to facilitate the formation of two C-C bonds operating via hydrogen (H2) evolution and obviating the need for external chemical oxidants.

Enhanced Catalytic Aryl Alkene Oxidation by Constructing Hierarchical Polyoxometalate‐Based Metal‐Organic Framework

AbstractAchieving highly selective oxidation of aryl alkenes to aldehydes is of great significance in chemical industry. Herein, the performance of catalytic aryl alkene oxidation is enhanced via constructing a hierarchical fractal polyoxometalate‐based metal–organic framework (POM@MOF) containing hierarchical pores and layered surface structure, which improve the mass transfer efficiency of substrates and increase the accessibility to active POMs clusters. Accordingly, the activity of fractal POM@MOF is increased by 4.8 times compared with microporous counterpart in 4‐tert‐butylstyrene oxidation to aldehyde product. This work paves a way for designing efficient catalysts for selective oxidation of aryl alkenes via increasing the accessibility of active sites and broadening the diffusion channels by hierarchical construction.

Merging of Light/Dark Palladium Catalytic Cycles Enables Multicomponent Tandem Alkyl Heck/Tsuji-Trost Homologative Amination Reaction toward Allylic Amines.

A visible light-induced palladium-catalyzed homologative three-component synthesis of allylic amines has been developed. This protocol proceeds via a unique mechanism involving two distinct cycles enabled by the same Pd(0) catalyst: a visible light-induced hybrid radical alkyl Heck reaction between 1,1-dielectrophile and styrene, followed by the "in dark" classical Tsuji-Trost-type allylic substitution reaction. This method works well with a broad range of primary and secondary amines, aryl alkenes, dielectrophiles, and in complex settings. The regiochemistry of the obtained products is primarily governed by the structure of 1,1-dielectrophile. Involvement of π-allyl palladium intermediates allowed for the control of stereoselectivity, which has been demonstrated with up to 95:5 er.

Unraveling Hydrogen Atom Transfer Mechanisms with Voltammetry: Oxidative Formation and Reactivity of Cobalt Hydride.

The utility of transition metal hydride catalyzed hydrogen atom transfer (MHAT) has been widely demonstrated in organic transformations such as alkene isomerization and hydrofunctionalization reactions. However, the highly reactive nature of the hydride and radical intermediates has hindered mechanistic insight into this pivotal reaction. Recent advances in electrochemical MHAT have opened up the possibility for new analytical approaches for mechanistic diagnosis. Here, we report a voltammetric interrogation of Co-based MHAT reactivity, describing in detail the oxidative formation and reactivity of the key Co-H intermediate and its reaction with aryl alkenes. Insights from cyclic voltammetry and finite element simulations help elucidate the rate-limiting step as metal hydride formation, which we show to be widely tunable based on ligand design. Voltammetry is also suggestive of the formation of Co-alkyl intermediates and a dynamic equilibrium with the reactive neutral radical. These mechanistic studies provide information for the design of future hydrofunctionalization reactions, such as catalyst and silane choice, the relative stability of metal-alkyl species, and how hydrofunctionalization reactions utilize Co-alkyl intermediates. In summary, these studies establish an important template for studying MHAT reactions from the perspective of electrochemical kinetic frameworks.

Selective Electrochemical Benzylic C(sp3)−H Oxidations in Fluoroalcohols

AbstractA site‐selective electrochemical benzylic C(sp3)−H oxidation reaction of aryl alkanes has been reported for synthesis of the desired products. This method significantly expands the scope and enhances the selectivity of aryl aldehydes and fluorinated ethers. Electricity is used as a sustainable oxidant and promote H2 evolution. This protocol is eco‐friendly and easy to handle as it uses a simple undivided cell in mild conditions without employing any catalyst and oxidant.

Stereoselective Synthesis of Multisubstituted Alkenes via Ruthenium-Catalyzed Remote Migration Arylation of Nonactivated Olefins.

Polysubstituted alkenes are an important class of organic intermediates that widely exist in various natural products and drug molecules. Herein, we reported a stereoselective synthesis of multisubstituted alkenes via ruthenium-catalyzed remote migration arylation of nonactivated olefins. This strategy exhibited wide substrate suitability and excellent functional group tolerance. In addition, we demonstrated the indispensable role of two types of ruthenium through mechanism experiments.

Synthesis and Palladium-Catalyzed Cross-Coupling of an Alkyl-Substituted Alkenylboronic Acid Pinacol Ester with Aryl Bromides

The palladium-catalyzed cross-coupling reaction of alkyl-substituted alkenylboron reagents with aryl halides is a versatile method to introduce a hydrophobic hydrocarbon chain onto organic compounds of interest. The application of the cross-coupling reaction is enabled by synthetic methods for the preparation of alkenylboron reagents. The geometrically pure, alkyl-substituted alkenylboron reagent, (E)-octenylboronic acid pinacol ester, was prepared by 9-BBN-catalyzed hydroboration reaction of 1-octene with pinacolborane in refluxing 1 M THF solution. This reagent was then evaluated in palladium-catalyzed cross-coupling reactions with aryl bromides. The highest yield of the (E)-1-phenyloctene was obtained when SPhos was used as the ligand, K2CO3 was used as the base, and DMF was used as the reaction solvent. Other electron-rich, electron-poor, sterically hindered, and heteroaromatic substrates produced the corresponding (E)-1-phenyloctene derivatives in moderate to good yield. KEYWORDS: Organic synthesis; Aryl alkene synthesis; Palladium-catalyzed cross-coupling; Suzuki-Miyaura reaction; Stereocontrolled alkene preparation; Hydroboration; 9-Borobicyclo[3.3.1]nonane; Reaction optimization

Electronic influence of pyrazole-appended pyridine/pyrazine based N,N,N-tridentate ligands on Ru complexes: Impact on selectivity of catalytic alkene oxidation with mild oxidant NaIO4

Three discrete Ru(II) complexes [Ru(L1)(bpy)Cl]Cl (1), [Ru(L1)(phen)Cl]Cl (2) and [Ru(L2)(bpy)Cl]Cl (3) have been prepared with two different pyridine/pyrazine based tridentate ligands L1 and L2, with one bipyridine/phenanthroline and one chloride as co-ligands. These complexes are characterized fully via spectroscopic and crystallographic techniques. The crystal structures of the complexes revealed the discrete monomeric structures. The Density Functional Theory (DFT) calculations showed that for complexes 1 and 3, the highest occupied molecular orbital (HOMO) is metal-centered whereas the lowest unoccupied molecular orbital (LUMO) is centered on the bpy ligand in 1, but interestingly it is based on the ligand L2 in case of the complex 3. Also, both the HOMO and LUMO are relatively more stabilized in 3 in comparison to 1. This fact implies very good π-acceptor nature of the ligand L2. This is reflected on the redox behavior of the complexes where around 200 mV anodic shift of the RuII/III redox potential was observed in 3 as compared to complex 1. This electronic influence of the ligands L1 and L2 impacted remarkably in the catalytic behavior of their Ru-complexes (1–3). Thus, the catalysts 1 and 2 were found to oxidize aryl alkenes to the corresponding acid products with high selectivity, whereas the catalyst 3 was selective toward the formation of aldehydes only, in the presence of only 2.5–3.0 equiv. of NaIO4 as the mild oxidant.

Trifluoromethylative Bifunctionalization of Alkenes via a Bibenzothiazole-Derived Photocatalyst under Both Visible- and Near-Infrared-Light Irradiation

The incorporation of trifluoromethyl groups into organic molecules such as agrochemicals and pharmaceuticals has attracted a significant amount of interest because they will impact the binding ability, lipophilicity, metabolic stability, and chemical stability of the resulting molecules. Over the past few years, photocatalytic trifluoromethylation of aryl alkenes has been reported, which typically requires precious Ru/Ir-containing photocatalytic systems. Herein, we report a metal-free organic photocatalyst composed of a bibenzothiazole core and two imine-bridged methoxyphenyl substituents (dBIP–OMe), which is able to drive trifluoromethylative bifunctionalization of alkenes photocatalytically without the use of any sacrificial reagents. Mechanistic studies reveal two consecutive single-electron-transfer steps between the excited dBIP–OMe*, the CF3 precursor (Umemoto’s reagent), and the alkene substrate. Substrate scope studies demonstrated that our trifluoromethylative bifunctionalization strategy using dBIP–OMe is applicable for both aryl and aliphatic alkenes. Furthermore, a variety of nucleophiles, such as H2O, acetate, cyanide, azide, etc., can be readily incorporated into the carbocation intermediate once the foremost trifluoromethylation step is accomplished, substantially broadening the application scope of this photocatalytic method. Finally, taking advantage of the two-photon absorption capability of dBIP–OMe in the near-infrared region, we demonstrated that the hydroxytrifluoromethylation of styrene could be achieved using an inexpensive 740 nm LED as the sole light source.

Precision Deuteration Using Cu-Catalyzed Transfer Hydrodeuteration to Access Small Molecules Deuterated at the Benzylic Position.

A highly regio- and chemoselective Cu-catalyzed aryl alkyne transfer hydrodeuteration to access a diverse scope of aryl alkanes precisely deuterated at the benzylic position is described. The reaction benefits from a high degree of regiocontrol in the alkyne hydrocupration step, leading to the highest selectivities reported to date for an alkyne transfer hydrodeuteration reaction. Only trace isotopic impurities are formed under this protocol, and analysis of an isolated product by molecular rotational resonance spectroscopy confirms that high isotopic purity products can be generated from readily accessible aryl alkyne substrates.