Reaction Of Arenes Research Articles

C−H Bond Activation in Ru‐Catalyzed Reactions of Arenes with Olefins: Theoretical Insights into Hydroarylation and Oxidative Coupling Mechanisms

AbstractA detailed mechanistic density functional theory (DFT) and coupled cluster study of Csp²−H activation in benzene and methyl acrylate by the catalyst RuClm(CO)n (m=2,3; n=0–4) is presented. We trace the entire reaction pathways from the precursor to the active form of the catalysts followed by catalytic hydroarylation and oxidative coupling reactions. Our results reveal that both computational methods provide very similar qualitative pictures, but only the coupled cluster DLPNO‐CCSD(T1) results are quantitatively consistent with experiment. At the latter level of theory, the Ru(II) and Ru(III) catalyst precursors transform into the same active form of the catalyst, which explains the experimental results. Oxidative addition is extremely endergonic, especially in the presence of CO. Oxidative hydrogen migration (OHM) occurs in complexes with a low Ru coordination number and leads to olefine hydroarylation. Strongly bound carbonyl ligands suppress this interaction. Concerted metalation‐deprotonation (CMD) of the aromatic C−H bond and σ‐bond metathesis mechanisms of catalyst regeneration do not involve Ru−H bonding and form the energetically favorable catalytic cycle of the oxidative coupling reaction. The key interaction in CMD mechanisms consists of proton abstraction by an inner‐sphere Cl‐anion. Carbonyl ligands facilitate CMD by weakening the Ru−Cl bond. An excess of CO slows the interaction by leading to replacement of the reactants in the Ru coordination sphere.

Real-time air concentrations and turbulent fluxes of volatile organic compounds (VOCs) over historic closed landfills to assess their potential environmental impact

For the first time, emission/deposition fluxes of volatile organic compounds (VOCs) and H2S from a historic closed landfill site in Southern Italy were determined by Eddy Covariance (EC) using Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS). This was done in two field campaigns of one week performed in July and October 2016, where fluxes of CO2 and CH4 were also measured. Many compounds not previously identified in the biogas were detected by PTR-TOF-MS, but only in July some of them produced positive fluxes exceeding the flux limit of detection. Methanol was the most emitted compound with an average flux of 44.20 ± 4.28 μg m−2 h−1, followed by toluene with a mean flux of 18.97 ± 2.47 μg m−2 h−1. Toluene fluxes were 10 times higher than those of benzene, fitting rather well with values previously measured in the biogas. VOCs emission fluxes of monoterpenes and highly reactive arenes did not reflect, however, the biogas composition. This, combined with tiny emissions of VOC oxidation products, suggests that landfill emissions underwent some photochemical degradation before being dispersed in the atmospheric boundary layer (ABL). Deposition fluxes of some VOCs emitted from the sea was also observed in July. No relevant VOC fluxes were instead measured in October, suggesting that temperature was the variable controlling most landfill emission. Albeit small, summer landfill emissions from the investigated site can have an impact on the population living nearby, because they contain or still generate compounds that causing nuisance.

Direct C–H amination reactions of arenes with N-hydroxyphthalimides catalyzed by cuprous bromide

An efficient Cu-catalyzed strategy for the direct C–H amination of arenes in high yields using N-hydroxyphthalimide as the amidyl radical precursor under air is reported. A possible mechanism is proposed that proceeds via a radical reaction in the presence of CuBr and triethyl phosphite.

TfOH/Hexafluoroisopropanol-Promoted Friedel–Crafts Reaction of Arenes with Aliphatic Epoxides or Alcohols

TfOH/Hexafluoroisopropanol-Promoted Friedel–Crafts Reaction of Arenes with Aliphatic Epoxides or Alcohols

Generation of a transient base-stabilised arylalumylene for the facile deconstruction of aromatic molecules.

While a stable base-free arylalumylene bearing a sterically encumbered terphenyl substituent has been reported previously, we herein report that our attempts to form a base-stabilised arylalumylene bearing a relatively small terphenyl substituent and an N-heterocyclic carbene base led instead to a “masked” dialumene (LRAl Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> AlRL), self-stabilised by one peripheral aromatic group. Intriguingly, examining the behavior of this species or its transient dialumene formed from reducing the diiodoarylalane in aromatic solvents under different conditions reveals that they both decouple into the desired base-stabilised arylalumylene. This transient acyclic, dicoordinate alumylene is highly reactive, deconstructing benzene and toluene to furnish dialuminium derivatives of pentalene, providing the first example of a neutral AlI compound able to deconstruct these less reactive arenes. Computational insights were also gained on the dialumene dissociation and on the mechanism of arene deconstruction by alumylene.

Regioselective iodination of activated arenes using KI-DMSO in aqueous hydrochloride

The KI-DMSO in aqueous hydrochloride has been utilized for selective iodination of activated arenes. The iodination of substrate such as hydroxyacetophenones, amines, phenols, anisole and toluene took place with high regioselectivity and mono-iodination was found to occur. The electron releasing substituents (–CH3, –OCH3, –OH, –NH2) exclusively form para substituted product while ortho-iodination occurred only when para-position was blocked by other substituents. The method is simple and noteworthy for reactive arenes with comprises some advantages as easy reaction procedure, short reaction time (5–12 min.) and fair to good yield of aryl iodides (65–90%). The structure of aryl iodide was established on the basis of spectral and elemental data.

Electrosynthesis 2.0 in 1,1,1,3,3,3‐Hexafluoroisopropanol/Amine Mixtures

AbstractThe intention of this review is to highlight the innovative electrolyte combination of 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) with tertiary nitrogen bases in electro‐organic synthesis. This easy applicable and promising mixture is not yet well established in electro‐organic synthesis, but expands the various possibilities in the latter. Combinations of fluorinated alcohols with nitrogen bases form highly conductive electrolyte systems, which can be evaporated completely. Consequently, no additional supporting electrolyte is required and work‐up procedures are tremendously simplified. With this electrolyte mixture carbon‐carbon homo‐ and cross‐coupling reactions of arenes and phenols have been established with substrates that have not been previously susceptible to the anodic dehydrogenative coupling reaction. The intermediate installation of highly fluorinated alkoxy moieties can be exploited for subsequent conversions as well as various benzylic functionalization, including asymmetric transformations. These transformations show unique selectivity and functional group tolerance making them highly applicable to the synthesis of sophisticated structural motifs, including natural products.

The Steric Effect in Green Benzylation of Arenes with Benzyl Alcohol Catalyzed by Hierarchical H-beta Zeolite

For decades the steric effect was still ambiguously understood in catalytic benzylation reactions of arenes with benzyl alcohol, which limited the green synthesis of phenylmethane derivates in industrial scale. This research applies a series of silica–alumina beta zeolites to systematically evaluate factors like catalyst porosity, reactants molecule size, and reaction temperature on catalytic benzylation. First, a suitable hierarchical beta zeolite catalyst was screened out by X-ray powder diffraction, N2 adsorption−desorption, and probe benzylation with p-xylene. In the following substrates expanding study, for a typical benzylation of benzene, it showed extraordinary performance among literature reported ones that the conversion was 98% while selectivity was 90% at 353 K only after 10 min. The steric effect of aromatics with different molecular sizes on benzylation was observed. The reaction activities of four different aromatics followed the order: benzene > toluene > p-xylene > mesitylene. Combined with macroscopic kinetic analysis, this comprehensive study points out for the first time that the nature of this steric effect was dominated by the relative adsorption efficiency of different guest aromatic molecules on the host zeolite surface.

Alkylation of Aromatic Hydrocarbons with 2-Methyl-2-Vinyl-gem-Dichlorocyclopropane over Zeolite Catalysts

It has been found as a result of the investigation of the catalytic properties of various microporous zeolites (of FAU, BEA, MOR, and MFI structural types) and a micro–meso–macroporous H-Ymmm zeolite (FAU) in the alkylation reaction of arenes (benzene (II) and toluene (III)) with the unsaturated compound 2-methyl-2-vinyl-gem-dichlorocyclopropane (I) that the reaction proceeds with the formation of chloroalkylarenes [1-(2,2-dichloro-1-methylcyclopropyl)ethyl]benzene (IV) and 1-[1-(2,2-dichloro-1-methylcyclopropyl)ethyl]-4-methylbenzene(V). Compounds IV and V are the most selectively formed over H-Beta (up to 82%) and H-Ymmm (up to 79%) zeolite catalysts with a high conversion of I (from 90% to full). It has been shown that high selectivity for chloroalkylarenes IV and V is achieved at 100°C, an arene : unsaturated compound molar ratio of 8 : 1, a catalyst concentration of 20 wt % of the reaction mass, and a reaction time of 2 h.

Synthesis of Azine- and Hydrazone-Based Triarylmethanes

Firstly, a series of new formylated-triarylmethanes (FTRAMs) were synthesized via the Friedel–Crafts reaction of arenes with terephthalaldehyde or isophthalaldehyde in the presence of silica sulfuric acid (SSA) under solvent-free conditions. Secondly, a series of new azines and hydrazones derivatives of formylated-triarylmethanes were synthesized in good yields. The structures of all the compounds were confirmed by elemental analysis, IR, 1H NMR and 13 C NMR spectroscopy.

Green, Mild, and Efficient Friedel-Crafts Benzylation of Scarcely Reactive Arenes and Heteroarenes under On-Water Conditions.

Metal-free Friedel-Crafts benzylation (FCB) of scarcely reactive arenes and heteroarenes was performed under on-water conditions by an environmentally sustainable procedure. The catalytic strategy exploits the hydrophobicity of the resorcinarene macrocycle 1 a. The proposed mechanism is based on the activation of benzyl chloride by H-bonding interactions with catalyst 1 a. In fact, under on-water conditions the hydrophobic amplification of the strength of the H-bonding interactions between the OH groups of the resorcinarene catalyst and the chlorine atom of benzyl chloride leads to polarization of the C-Cl bond, which consequently promotes electrophilic attack of the π nucleophile. Thus, many arenes and heteroarenes were efficiently benzylated under mild on-water conditions by using resorcinarene 1 a as catalyst. The FCB of benzene is industrially relevant for the synthesis of diphenylmethane, and hence the on-water procedure was extended to the gram-scale synthesis of diphenylmethane, starting from benzene and benzyl chloride in the presence of resorcinarene catalyst 1 a.

Synthesis of Benzamide Derivatives by the Reaction of Arenes and Isocyanides through a C–H Bond Activation Strategy

A carbon–carbon bond formation reaction between isocyanides and benzene derivatives is reported. In contrast to traditional cross-coupling reactions, which require aryl halides or pseudohalides, we use a palladium catalyst to generate the aryl–palladium through C–H bond activation of arenes. This method offers an attractive approach to a range of benzamides from readily accessible benzene derivatives.

Recent Advances in the Intramolecular Reactions of Epoxides with Arenes and Heteroarenes

AbstractOver the years, the reactions and applications of epoxides have attracted the attention of many research groups. Intramolecular reactions of epoxides with arenes, termed epoxide–arene cyclizations (EACs) in this Focus Review, are the intramolecular C−C bond‐forming reactions of arenes with tethered epoxides and represent a particular type of epoxide‐derivatization reactions. EACs have been successfully applied to the synthesis of various benzo‐fused carbo‐ and heterocycles as reliable C−C bond‐forming reactions with complete atom economy. In this Focus Review, results in the literature since 2011 on the development of EACs are presented. Different aspects of substrate reactivities, the regio‐ and stereochemical outcomes of these reactions, and their proposed mechanisms are discussed.

The effect of the coordination sphere of the platinum catalyst on the course of the direct С–С coupling in the systems PtII–ArH–ArI–base. The experimental and theoretical (DFT) study

The composition of coupling products in reaction of arenes with aryl iodides catalyzed with Pt(phen)Cl2, Pt(bipy)Cl2, Pt(py)2Cl2 and K2PtCl4 complexes was studied. Based on quantum-chemical calculations of the charges on platinum atoms, the energies of the frontier molecular orbitals of the metal complexes and substrates an approach is proposed to forecasting the effect of the structure of the catalyst on the direction of the reaction towards the homo or cross-coupling.

Furanyl Alcohols as Alkylating Reagents in Friedel–Crafts Reaction of Arenes

Furanyl alcohols react with arenes by a variant of the Friedel–Crafts reaction to give benzyl furans with fairly satisfying yields. The reaction is mediated by Tf2O and occurs with reduced times in the presence of Ph3PO. Some prepared compounds exhibit a lignan‐like backbone.

Peracetic Acid Mediated sp2 C–H Selenation of Arenes

Peracetic acid promoted C–Se coupling reaction of arenes with diselenides under metal-free and solvent-free conditions has been described. The resulting selenide ethers were obtained in good to excellent yields. Peracetic acid provided the selenide ethers via sp 2 C–H selenation whereas previously in case of DTBP sp 3 C–H selenation was observed.

ChemInform Abstract: Palladium‐Catalyzed Decarboxylative ortho‐Ethoxycarbonylation of O‐Methyl Ketoximes and 2‐Arylpyridines with Potassium Oxalate Monoester.

AbstractThe Pd‐catalyzed reaction of arenes (I) bearing a directing O‐methyl ketoxime group with potassium oxalate monoester leads selectively to ortho‐ethoxycarbonylated products (III).

ChemInform Abstract: Eaton′s Reagent‐Mediated Domino π‐Cationic Arylations of Aromatic Carboxylic Acids to Iasi‐Red Polymethoxylated Polycyclic Aromatic Hydrocarbons: Products with Unprecedented Biological Activities as Tubulin Polymerization Inhibitors.

AbstractThe π‐cationic arylation of methoxy substituted benzoic acids with reactive arenes [e.g. (II)] is developed to provide an optimized synthetic route to phenstatin (V).

Highly ortho‐Selective Trifluoromethylthiolation Reactions using a Ligand Exchange Strategy

AbstractThe trifluoromethylthio group (SCF3) is a highly privileged modifier for drug molecules. Direct CH trifluoromethylthiolation reactions are highly valuable synthetic tools for the late‐stage modification of drug candidates, which have so far been underexplored. We report a palladium‐catalyzed ortho‐selective mono‐trifluoromethylthiolation reaction of arenes. The reaction proceeds through a key ligand exchange pathway using readily available silver trifluoromethylthiolate (AgSCF3). Acetic acid was found to be crucial to minimize oxidative dimerization of the starting materials and to facilitate the “SCF3−” transfer. We expect this strategy to have broad applications in CH functionalization reactions using a stand‐alone oxidant and various anions.magnified image

The 2,4-dimethyl-7-pentafluorosulfanyl-5-(trifluoromethyl)dibenzo[b,d]thiophenium trifluoromethanesulfonate: The SF5-analog of Umemoto salt

The SF5-analog of the Umemoto salt was synthesized in just two steps by combining our recently reported SF5-biaryl synthesis, via Suzuki coupling with 4-(pentafluorosulfanyl)benzenediazonium tetrafluoroborate, with Magnier's one-pot synthesis of dibenzothiophenium salts employing CF3SO2Na and triflic anhydride. The trifluoromethylating power of this novel onium salt toward reactive arenes was tested in a survey study on small scale.