Transition metal free K2CO3 mediated thioarylation,selenoarylation and arylation of 2-aminomaleimides at ambient temperature

Transition metal free thioarylation, selenoarylation and arylation of 2-aminomaleimide, using thiophenols, diaryl diselenides and arylhydrazine hydrochlorides respectively, has been reported in DMSO under aerobic condition in presence of K₂CO₃ at room temperature. The reaction occurs smoothly without prerequisite N-protection of 2-aminomaleimide. The synthesis of novel, polyfunctionalized maleimides has been achieved by the direct C–H activation of enamines. Thioarylation and selenoarylation are proposed to be proceeding via disulfides/diselenides and arylation has been proposed to be proceeding via aryl free radicals.     

A facile synthesis of (Z)-1, 6-disubstituted-7H-benzo[b][1,5]diazonin-7-one derivatives via arylation-allylation-RCM pathway of anthranilamide and isatoic anhydride

A facile and efficient method has been developed for the synthesis of (Z)-6-allyl-1-phenyl-1,2,5,6-tetrahydro-7H-benzo[b][1,5]diazonin-7-one and (Z)-1,6-diphenyl-1,2,5,6-tetrahydro-7H-benzo[b][1,5]diazonin-7-one from anthranilamide via N-arylation/N-allylation and from isatoic anhydride via ring opening/N-arylation/N-allylation followed by ring closing metathesis using Grubbs-II catalyst as a key step. Grubbs-II catalyst was found to be superior over Grubbs-I catalyst in terms of reaction time and yield of the product, and the routes developed were suitable to synthesize benzo fused nine membered nitrogen heterocycles. The requirement of diallylated substrates with protected amine and amide nitrogen is suitable for RCM has been established for the synthesis of diazoninone derivatives.     

Synthesis of C-Homoaporphines via Microwave-Assisted Direct Arylation

Representatives of the C-homoaporphine class of alkaloids have shown interesting biological activities. To date the synthesis of these molecules has never been attempted via a direct-arylation strategy. We report herein the first Pd-mediated intramolecular direct arylation in the synthesis of C-homoaporphines via the use of microwaves. Use of tricyclohexylphosphine tetrafluoroborate as ligand gave good percentage conversions and suppressed competing debromination with the substrates evaluated. This arylation strategy should be broadly useful in the synthesis of C-homoaporphine alkaloids as demonstrated herein in the synthesis of (±)-homonantenine.     

Palladium-catalyzed intramolecular arylation of pyrimidines: a novel and expedient avenue to benzannulated pyridopyrimidines

A new efficient protocol for the synthesis of benzannulated pyrido[2,3-d]- and pyrido[3,2-d]pyrimidines has been successfully accomplished via the palladium-catalyzed intramolecular arylation of C-H bond of pyrimidine moiety. The methodology has also been extended to the synthesis of pyrimido[5,4,-c]isoquinoline-2,4,6(1H,3H,5H)-trione derivatives in excellent yields.     

<Emphasis Type="Italic">N</Emphasis>-Propylphthalimide-substituted bis-(NHC)PdX<Subscript>2</Subscript> complexes: synthesis,characterization and catalytic activity in direct arylation reactions

Palladium-catalyzed direct arylation of heteroaromatics has become a popular method for producing carbon–carbon bonds via C–H bond activation. A wide diversity of heteroaromatics such as furan, thiophenes and thiazoles can be used for this reaction. This paper reports the synthesis of N-propylphthalimide-substituted bis-(NHC)PdX₂ complexes (NHC = N-heterocyclic carbene), and their catalytic activity in direct arylation reactions. The complexes have been prepared from Ag(I)NHC precursors by transmetallation and characterized by spectroscopy and elemental analysis. The bis-(NHC)PdX₂ complexes show excellent activity as catalysts in the direct arylation reactions of 2-n-butylfuran, 2-n-butylthiophene and 2-isopropylthiazole.     

Et-duphos-nickel-catalyzed asymmetric arylation of benzaldehyde derivatives bearing an ortho-Me2PhSi group with potassium aryltriolborates

The Ni-catalyzed asymmetric arylation of benzaldehydes bearing an ortho-masked H group with potassium aryltriolborates has been developed. The keys to success were (i) steric tuning of benzaldehyde derivatives with an ortho-Me₂PhSi group, and (ii) the use of potassium aryltriolborates as aryl sources.     

Palladium-catalyzed highly regioselective and stereoselective decarboxylative arylation of unactivated olefins with aryl carboxylic acids

Palladium(II)-catalyzed highly regioselective and stereoselective decarboxylative arylation of unactivated olefins with aryl carboxylic acids has been developed. This method is applicable to a variety of unactivated olefins, including allylamides, long chain functionalized olefins and purely aliphatic olefins, leads to the formation of linear E-configured products in high yields. Both electron-rich and electron-deficient aryl carboxylic acids are suitable arylation reagents. It was found that the choice of solvent, catalyst precursor and oxidant had an important influence on reaction efficiency. As a co-solvent and ligand, DMSO is critical to catalysis. This chemistry expands the scope of decarboxylative arylation of olefins with aryl carboxylic acids, and provides a rapid access to useful linear arylation products of unactivated olefins.     

An efficient synthesis of an 8-phenoxy aporphine derivative utilizing mono-ligated palladium ortho-phenol arylation

8-Aryloxy aporphines are a structurally diverse subset of alkaloids that display an array of biological activities. An efficient synthesis of an 8-phenoxy aporphine model compound has been developed utilizing Pictet-Spengler cyclization followed by biaryl bond formation using Pd-XPhos catalyzed ortho-phenol arylation. Biaryl bond formation using direct arylation is also compared. Finally, the stability of the 8-phenoxy aporphine model compound is discussed with potential implications for the isolation, structure elucidation and pharmacognosy of 7-dehydroaporphine natural products.     

A general method for regioselective Heck arylation of electron-rich N-acyl-N-vinylamine with aryl halides

A highly efficient protocol for the Pd-catalyzed regioselective Heck arylation of the electron-rich olefin N-acyl-N-vinylamine with aryl halides has been developed. In the presence of hydrogen-bond donor [H₂NiPr₂][BF₄] as an additive, this proceeds smoothly in isopropanol to afford exclusively the branched products in high yields.     

Solvent-free 1,6-conjugate arylation of para-quinone methides: A greener approach to unsymmetrical triarylmethanes

A highly efficient arylation of para-quinone methides (p-QMs) with N,N-dimethylaniline under solvent free condition has been developed, which proceeded via a para-toluenesulfonic acid (TsOH)-promoted 1,6-conjugated addition pathway. This methodology provided a green and sustainable methodology to construct various novel unsymmetrical triarylmethanes (TAMs) with the advantages of good functional group tolerance, scalability, and regioselectivity.     

Palladium-mediated fragmentation of meta photocycloadducts using carbon based electrophiles. Part 1

Substituted benzene derived meta photocycloadducts have been shown to undergo a fragmentation/arylation reaction under Heck reaction conditions to give bridged bicyclo[3.2.1] compounds in a highly atom-efficient manner. When an anisole derived meta photocycloadduct is used, a bridgehead ketone is generated. However, if an alkylbenzene derived meta photocycloadduct is used, a bridgehead alkene is formed. This strategy has been used to create novel enol ether and transient allyl silane compounds.     

Palladium-catalyzed arylation/cyclization/desulfonation cascades toward 4-aryl quinolin-2(1H)-ones with diaryliodonium salts

Palladium-catalyzed cascades of arylation/cyclization/desulfonation of ortho-aminocinnamate esters by using diaryliodonium salts afforded a wide range of 4-aryl quinolin-2(1H)-ones. As such, the desired 4-aryl quinolin-2(1H)-ones with potential biological activity has been synthesized in the yields of 34–96%.     

A mild and regioselective Ullmann reaction of indazoles with aryliodides in water

A mild and regioselective Ullmann reaction of indazoles with aryliodides has been developed as a general method for the synthesis of 1-aryl-1H-indazoles. Water was used as the solvent wherein Tween 20 (2% w/w) was added to form aqueous micelles to improve solubility of starting materials and accelerate reaction rate. This aqueous protocol allows the Ullmann reaction to proceed at a mild temperature (60 °C) within a short reaction time (2 h), which typically requires high temperatures (≥100 °C) and prolonged duration (≥24 h). The protocol demonstrated broad substrate scopes with good isolated yields and high regioselectivity (N-1 arylation over N-2 arylation) for 25 examples examined.     

Polynuclear isocyanide complexes of rhenium

The arylation of carbonylgold chloride with diarylzinc compounds yields either triarylgoldzinc or diarylgoldzinc chlorides, depending on the reactant ratio and the nature of the aryl group. The same reactions with diphenylcadmium and diphenylmercury yield exclusively diphenylgoldcadmium chloride and diphenylgoldmercury chloride, respectively. The reactions of the products with N,N,N′,N′-tetramethylethylenediamine and triphenylphosphine were studied.Phenylgold has been obtained as a very unstable solid from diphenylgoldzinc chloride and diphenylgoldmercury chloride.     

Syntheses of effectively-shielded N-heterocyclic carbene ligands

A novel type of N-heterocyclic carbene ligand, with a bicyclic motif at the non-carbenic carbons of an imidazolin-2-ylidene core, has been developed. This type of ligand formed an air and moisture stable silver complex even with N,N′-dimethyl NHC. Allylic arylation with a Grignard reagent catalyzed by copper complexes of the NHC ligands proceeded preferentially at the γ-position, indicating the effective steric shielding ability of this framework.     

Direct ortho-arylation of 2-arylbenzoxazoles via C-H activation

A new and highly regioselective arylation of 2-arylbenzoxazoles based on C-H activation has been developed. The results represent the first examples of palladium-catalyzed direct ortho-arylation of 2-arylbenzoxazoles and also provide a facile route for the synthesis of complicated structures containing arylated benzoxazoles moieties.     

Modified palladium-catalyzed regioselective ortho-arylation of sp C-H bond substrates with a low catalyst loading

A novel and generally applicable system for ortho-arylation of a broad range of sp² C-H bond substrates such as arylated benzoxazoles, acylated anilines, and pyridines has been developed. The arylation was performed in trifluoroacetic acid (TFA) under air by using PdCl₂ as the catalyst with a low catalyst loading of 1 mol %. And it was found for the first time that the addition of weak base K₃PO₄ to the acidic solvent could remarkably enhance the reaction rate. The arylated products were isolated in moderate to good yields with high regioselectivity for the substrates containing a meta-substituent. This arylation is tolerant with various functional groups such as CH₃, CH₃O, CH₃CO, Br, and Cl.     

Copper-promoted Chan-Lam coupling between enaminones and aryl boronic acids

A novel copper-promoted N-arylation of enaminones with aromatic boronic acids has been developed, which provides an efficient way to synthesize N-aryl enaminones with a broad substrate scope and excellent functional group compatibility. The N-aryl enaminones could be converted into a series of highly valuable building blocks and bioactive compounds. Notably, in comparison with traditional methods, this alternative approach provides accesses to N-aryl enaminones bearing multiple aromatic rings.     

Arylation with aryllead triacetates produced in situ by mercury-lead exchange

Reaction of a diarylmercury with lead tetraacetate to give an aryllead triacetate has been found to be a rapid reaction. The in situ generation of aryllead triacetates is thus an attractive alternative to the use of the purified reagents in the various electrophilic arylation reactions of these compounds.     

Radical-clock α-halo-esters as mechanistic probes for bisphosphine iron-catalyzed cross-coupling reactions

The mechanism of chiral bisphosphine iron-catalyzed C(sp²)-C(sp³) cross-coupling reactions has been studied via the synthesis of novel radical-clock α-halo-esters and quantum mechanical calculations. These results provide insights into the role of the substrate (halogen and substituents) in competing in-cage and out-of-cage arylation pathways and provide a basis for the future rational design of novel tandem cyclization-arylation reactions using bisphosphine-iron as catalysts.