Reversible Dehalogenation in On-Surface Aryl–Aryl Coupling

In the emerging field of on-surface synthesis, dehalogenative aryl–aryl coupling is unarguably the most prominent tool for the fabrication of covalently bonded carbon-based nanomaterials. Despite its importance, the reaction kinetics are still poorly understood. Here we present a comprehensive temperature-programmed x-ray photoelectron spectroscopy investigation of reaction kinetics and energetics in the prototypical on-surface dehalogenative polymerization of 4,4′′-dibromo-p-terphenyl into poly(para-phenylene) on two coinage metal surfaces, Cu(111) and Au(111). We find clear evidence for reversible dehalogenation on Au(111), which is inhibited on Cu(111) owing to the formation of organometallic intermediates. The incorporation of reversible dehalogenation in the reaction rate equations leads to excellent agreement with experimental data and allows extracting the relevant energy barriers. Our findings deepen the mechanistic understanding and call for its reassessment for surface-confined aryl–aryl coupling on the most frequently used metal substrates.     

CuI-catalyzed Synthesis of Aryl Thiocyanates from Aryl Iodides

Aryl thiocyanates are important compounds not only for their interesting biological properties, but also because of their use as a versatile starting material for many sulfur- containing aromatic compounds, including sulfonyl cyanides, sulfonic acids, sul…     

Aryl–Aryl Interactions in (Aryl-Perhalogenated) 1,2-Diaryldisilanes

Three 1,2-diaryltetramethyldisilanes X₅C₆-(SiMe₂)₂-C₆X₅ with two C₆H₅, C₆F₅, or C₆Cl₅ groups were studied concerning the importance of London dispersion driven interactions between their aryl groups. They were prepared from 1,2-dichlorotetramethyldisilane by salt elimination. Their structures were determined in the solid state by X-ray diffraction and for free molecules by gas electron-diffraction. The solid-state structures of the fluorinated and chlorinated derivatives are dominated by aryl–aryl interactions. Unexpectedly, Cl₅C₆-(SiMe₂)₂-C₆Cl₅ exists exclusively as an eclipsed syn-conformer in the gas phase with strongly distorted Si-C₆Cl₅ units due to strong intramolecular interactions. In contrast, F₅C₆-(SiMe₂)₂-C₆F₅ reveals weaker interactions. The contributions to the total interaction energy were analyzed by SAPT calculations.     

Overman Rearrangement of γ- Aryl Crotyl Alcohols: Effects of Aryl Substituents

Various α,α-methyl aryl allylic amines were synthesized from γ-aryl crotyl alcohols via thermal Overman rearrangement. Noteworthy is that the presence of the electron withdrawing groups at aryl group causes substantial increases in the reaction rates and product yields. The resulting trichloroacetamides were hydrolyzed to the corresponding amines in good yields.     

Convenient Synthesis of 5‐Aryl Uracils

A convenient one‐step synthesis of 5‐aryl uracils has been developed. The procedure involves heating ethyl 3‐hydroxy‐2‐arylpropenate with urea at 130°C, followed by base‐catalyzed cyclization. The method is simple and high yielding.     

Copper bis(2,2,6,6-Tetramethyl-3,5-heptanedionate)–Catalyzed Coupling of Sodium Azide with Aryl Iodides/Boronic Acids to Aryl Azides or Aryl Amines

This work reports an efficient protocol for the coupling reaction of aryl iodides/boronic acids with sodium azide to aryl azides/amines in the presence of copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate) Cu(TMHD)₂ catalyst. The Cu(TMHD)₂ catalyst is a structurally well-defined, O-containing, air- and moisture-stable, transition-metal complex and works at mild reaction conditions. It was observed that aryl azides can be reduced further to corresponding aniline derivatives using the same catalyst under basic reaction conditions for a prolonged period.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Pentamethylcyclopentadienylruthenium(II) Complexes: Synthesis,Characterization and Catalytic Activity in Aryl–Aryl Coupling

Ruthenium(II) complexes of the type [Ru(PPh₃)( ⁵-C₅Me₅)L] have been synthesized by the reactions of [RuCl(PPh₃)₂( ⁵-C₅Me₅)] with Schiff bases having the (N, O) donor atoms. The Schiff bases used in this study were prepared by condensing the appropriate aniline with salicylaldehyde or 2-hydroxy-1-naphthaldehyde in a 1:2 molar ratio respectively. The complexes were characterized by analytical, spectral (i.r., electronic and ¹H-n.m.r.) data. The new complexes have been used as catalysts in aryl–aryl coupling reactions.     

A Dual Palladium and Copper Hydride Catalyzed Approach for Alkyl–Aryl Cross-Coupling of Aryl Halides and Olefins

We report an efficient means of sp²–sp³ cross coupling for a variety of terminal monosubstituted olefins with aryl electrophiles using Pd and CuH catalysis. In addition to its applicability to a range of aryl bromide substrates, this process was also suitable for electron-deficient aryl chlorides, furnishing higher yields than the corresponding aryl bromides in these cases. The optimized protocol does not require the use of a glovebox and employs air-stable Cu and Pd complexes as precatalysts. A reaction on 10 mmol scale further highlighted the practical utility of this protocol. Employing a similar protocol, a series of cyclic alkenes were also examined. Cyclopentene was shown to undergo efficient coupling under these conditions. Lastly, deuterium-labeling studies indicate that deuterium scrambling does not take place in this sp²-sp³ cross coupling, implying that β-hydride elimination is not a significant process in this transformation.     

Synthesis of a New Aryl Ether Ketone Polymer

SemicrystallinearyletherketonepolymerssuchasPEEKbelongtoaclassofmaterialsknownasengineeringthermoplastics.PEEKexhibitsarelativelyhighdegreeofcrystallinityandameltingpoint(T.)of335"C.Ontheotherhand,PEEKsuffersfrompoorcreepbehavioraboveitsrelativelylowglasstransitiontemperature(T,)of143"C.Therefore,thesynthesisofnewvariantsisthefocusofmuchresearchl'2.Thesenewvariantsareusuallysemicrystallineinnatureandexhibithighmeltingpoints.Thisresultsinprocessingdifficulties,whichhascreatedaneedforpoly…     

Synthesis of α-Arylated Esters from Aryl Halides

The preparation of α-arylalkanoic acid esters has received significant attention, not only due to these compounds are important industrial materials, but also some of them are nonsteroidal anti-inflammatory drugs (NSAID)1. Arylation of β-dicarbonyl carb…     

Controlling Regioselectivity in Palladium-Catalyzed C−H Activation/Aryl–Aryl Coupling of 4-Phenylamino[2.2]paracyclophane

Selective activation/functionalization of C−H bonds has emerged as an atom- and step-economical process at the forefront of modern synthetic chemistry. This work reports palladium-catalyzed exclusively para-selective C−H activation/aryl–aryl bond formation with a preference over N-arylation under the Buchwald–Hartwig amination reaction of 4-phenylamino[2.2]paracyclophane. This innovative synthetic strategy allows a facile preparation of [2.2]paracyclophane derivatives featuring disparate para-substitutions at C-4 and C-7 positions in a highly selective manner, gives access to a series of potential candidates for [2.2]paracyclophane-derived new planar chiral ligands. The unprecedented behavior in reactivity and preferential selectivity of C−C coupling over C−N bond formation via C−H activation is unique to the [2.2]paracyclophane scaffold compared to the non-cyclophane analogue under the same reaction conditions. Selective C−H activation/aryl–aryl bond formation and sequential C−N coupling product formation is evidenced unambiguously by X-ray crystallography.     

Ammonium Chloride Promoted Palladium-Catalyzed UIImann Coupling of Aryl Bromide

In water, ammonium chloride was found to promote palladium-catalyzed Ullmann coupling reactions of aryl bromides. In the presence of Pd/C, zinc, NH4Cl, and water, coupling of various aryl bromides was carried out smoothly to afford the corresponding homocoupling products in moderate yields.     

Ammonium Chloride Promoted Palladium-Catalyzed Ullmann Coupling of Aryl Bromide

The Ullmann coupling reaction is one of the most useful methods for the synthesis of symmetrical biaryls. It is usually carried out with copper as a reagent.1 However, it generally requires more than a stoichiomet-ric amount of copper and high reaction temperature. In recent years, various reagents, especially combination of the transition metal with reducing reagents,2-6 were proposed to overcome these problems. For example, Li and co-workers2a,2b have reported the Pd/C and zinc-mediated Ul…     

Nickel-Catalyzed Aminocarbonylation of Aryl Iodides with 1 atm CO

Reported here is a nickel-catalyzed aminocarbonylation of aromatic iodides with (hetero)aryl anilines and alkyl amines under atmospheric CO pressure. The reaction features with broad substrate scope with excellent functional group tolerance, providing an expedient method for the construction of amide analogues. Notably, amino alcohols can be selectively transformed into the corresponding amides successfully without interfering the hydroxyl group under the current standard conditions.     

Synthesis of α,α-Difluoroethyl Aryl and Heteroaryl Ethers

Fluorine plays a critical role in modern medicinal chemistry due to its unique properties, and new methods for its incorporation into target molecules are of high interest. An efficient new method for the preparation of aryl-α,α-difluoroethyl ethers (4) via addition of aryl and heteroaryl alcohols (1) to commercially available 2-bromo-1,1-difluoroethene (2) and subsequent hydrogenolysis is presented. This procedure is an attractive alternative to existing methods that employ harshly reactive fluorinating systems such as xenon difluoride and hydrogen fluoride.     

Base-Free Pd-Catalyzed C−Cl Borylation of Fluorinated Aryl Chlorides

Catalytic C−X borylation of aryl halides containing two ortho-fluorines has been found to be challenging, as most previous methods require stoichiometric amounts of base and the polyfluorinated aryl boronates suffer from protodeboronation, which is accelerated by ortho-fluorine substituents. Herein, we report that a combination of Pd(dba)₂ (dba=dibenzylideneacetone) with SPhos (2-dicyclohexylphosphino-2’,6’-dimethoxybiphenyl) as a ligand is efficient to catalyze the C-Cl borylation of aryl chlorides containing two ortho-fluorine substituents. This method, conducted under base-free conditions, is compatible with the resulting di-ortho-fluorinated aryl boronate products which are sensitive to base.     

Polyethylene Glycol–Promoted Dialkyl,Aryl/Heteroaryl Phosphonates

A new, straightforward polyethylene glycol–promoted method for Michaelis–Arbuzov rearrangement has been described.     

Facile One‐Pot Synthesis of 2‐Aryl‐substituted Nitriles and 2‐Aryl‐3‐keto Nitriles via Benzyne Reaction

2‐Aryl‐substituted nitriles were prepared in good to excellent yields in a one‐pot reaction by the reaction of benzyne, generated using neutral conditions from (phenyl)[o‐(trimethylsilyl)‐phenyl]iodonium triflate, and 2‐lithionitriles. 3‐Keto nitriles substituted at the 2‐position were obtained in good yields when these reactions were trapped with acid chlorides. The mechanism of the benzyne reaction in terms of a N‐lithiobenzocyclobutanimine intermediate is discussed.     

Cu（OAc）2/Pyrimidines-Catalyzed Cross-coupling Reactions of Aryl Iodides and Activated Aryl Bromides with Alkynes under Aerobic, Solvent-free and Palladium-free Conditions

Excellent results have been achieved in the Cu（OAc）2-catalyzed Sonogashira cross-couplings of aryl iodides and activated aryl bromides utilizing TBAF （tetrabutylammonium fluoride） as the base and 4,6-dimethoxypyrimidin-2-amine as the ligand. It is noteworthy that the reaction is conducted under aerobic, solvent-free and palladium-free conditions.     

Synthesis of Methyl N‐Aryl Oxamate Using Soluble Polymer Support

A variety of methyl N‐aryl oxamates were synthesized using poly(ethylene glycol) (PEG) as a soluble polymer support and a monoproctection group with excellent yields.