Catalytic Arylation Research Articles

Enantioselective catalytic synthesis of ethyl mandelate derivatives using Rh(I)–NHC catalysts and organoboron reagents

Herein we describe for the first time the enantioselective catalytic arylation of ethyl glyoxalate using phenylboron reagents and chiral rhodium(I)–NHC catalysts. KOtBu was the base of choice, along with tert-amyl alcohol as the solvent. A novel chiral bis-imidazolium salt was synthesized and evaluated for the first time in this catalytic transformation. Although moderate enantioselectivities (up to 34% ee) were obtained for the phenylation reaction, despite the excellent yields, very low enantioselectivities were obtained using other arylboronic acids with a variety of chiral rhodium(I)–NHC catalysts.

Sp2 C–H bond activation in water and catalytic cross-coupling reactions

The metal-catalysed successive activation and functionalisation of sp(2) C-H bonds is the at heart of synthetic innovations for the development of C-C bond cross-coupling processes. Against expectation catalytic C-H bond transformations can be performed in water as an available, renewable, safe solvent but most importantly as a partner improving the catalyst activity. The objective of the review is to present the catalytic successes for C-H bond transformations in water, discovered mainly during the last six years and involving mostly palladium and ruthenium catalysts, often with the help of a carboxylate partner for the initial key C-H bond deprotonation. Water is beneficial for the direct catalytic arylation with (hetero)aryl halides of functional arene ortho C-H bonds with pyridine, pyrazole, oxazoline, imine, urea, amide… directing groups leading to functional biaryl derivatives, polyheterocycles and polydentate ligands. Metal-catalysed activation of the sp(2) C-H bond in water also allows the cross-coupling reaction of two different C-H bonds in the presence of an oxidant and regioselective alkenylations of arenes, heterocycles and functional alkenes are now controlled. Annulation reactions via insertion of alkynes into both activated C-H and heteroatom-hydrogen bonds in water constitute new routes to heterocycles.

Direct C-arylation of polyfluoroarenes with diaryliodonium salts via Pd(OAc)2-catalysis

A novel approach towards the Pd-catalyzed arylation of electron-deficient polyfluoroarenes with diaryliodonium salts was developed. The desired fluorinated biaryls were synthesized in good yields. The mechanistic insights involving the PdII/IV catalytic cycle for the present reaction were discussed, which will be helpful in the understanding of catalytic arylations with diaryliodonium salts.

ChemInform Abstract: Palladium‐Catalyzed Direct Arylation of 5‐Chloropyrazoles: A Selective Access to 4‐Aryl Pyrazoles.

AbstractA number of 4‐arylated pyrazoles can be prepared efficiently.

A New Method To Generate Arene-Terminated Si(111) and Ge(111) Surfaces via a Palladium-Catalyzed Arylation Reaction

Formation of silicon-aryl and germanium-aryl direct bonds on the semiconductor surface is a key issue to realize molecular electronic devices, but the conventional methods based on radical intermediates have problems to accompany the side reactions. We developed the first example of versatile and efficient methods to form clean organic monolayers with Si-aryl and Ge-aryl bonds on hydrogen-terminated silicon and germanium surfaces by applying our original catalytic arylation reactions of hydrosilanes and hydrogermanes using Pd catalyst and base in homogeneous systems. We could immobilize aromatic groups with redox-active and photoluminescent properties, and further applied in the field of rigid π-conjugated redox molecular wire composites, as confirmed by the successive coordination of terpyridine molecules with transition metal ions. The surfaces were characterized using cyclic voltammetry (CV), water contact angle measurements, X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, and atomic force microscopy (AFM). Especially, the AFM analysis of 17 nm-long metal complex molecular wires confirmed their vertical connection to the plane surface.

ChemInform Abstract: Catalytic Arylation of a C—H Bond in Pyridine and Related Six‐Membered N‐Heteroarenes Using Organozinc Reagents.

AbstractArylation of electron‐deficient N‐heteroarenes is achieved either with organozinc reagents through nickel catalysis or with arylboronic acids generating the active zinc reagent in situ.

Efficient catalytic aryl amination of bromoarenes using 3-iminophosphine palladium(II) chloride

While pursuing the development of new hydroamination catalysts, a 3-iminophosphine palladium(II) chloride complex [(3IP)PdCl2] was synthesized that has subsequently proven to be an effective precatalyst for the aryl amination of bromoarenes. This (3IP)PdCl2 complex has been utilized in the catalytic aryl amination of both bromobenzene and bromopyridine derivatives, specifically yielding excellent activity in coupling reactions involving bromobenzene, 4-bromotoluene, and 2-bromopyridine. Using a standard set of catalytic conditions, many alkyl and aryl amines have been investigated as coupling partners in the aryl amination of bromoarenes. In general, secondary alkyl amines and ortho-substituted anilines proved to be the best substrates for this reaction, commonly giving quantitative conversion to products, while primary amines and other anilines gave only poor to moderate results. Catalytic screening data, product yields, and full characterization of isolated products are included.

ChemInform Abstract: Development of Efficient Catalytic Arylation of Aldehydes with Thioether‐Imidazolinium Carbene Ligands

AbstractReview: 74 refs.

Expeditious and novel synthesis of α-hydroxyesters via rhodium–NHC catalyzed arylation of ethyl glyoxalate

The rhodium–NHC catalyzed arylation reaction of ethyl glyoxalate with aryl and alkyl boronic acids provides an efficient method for the synthesis of α-hydroxyesters. A wide range of α-hydroxyesters (up to 12) were prepared in good to excellent yields. KOtBu was the base of choice, along with tert-amyl alcohol as the solvent. As far as we are aware, this is the first report of this catalytic arylation, using rhodium–NHC catalysts with this specific substrate type.

Catalytic Arylation of a CH Bond in Pyridine and Related Six‐Membered N‐Heteroarenes Using Organozinc Reagents

Despite significant advances in the catalytic direct arylation of heteroarenes, the application of this reaction to pyridines has been met with limited success. An oxidative nucleophilic arylation strategy has been developed to overcome this problem. Pyridine, pyrazine, quinolone, and related electron-deficient N-heteroarenes can be arylated at the most electrophilic site using the developed nickel-catalyzed reaction. This protocol serves as a complementary method to catalytic direct arylation reactions.

Stereoselective homogeneous catalytic arylation of methyl methacrylate: Experimental and computational study

Catalytic systems trans-[PdCl2(DEA)2]/DEA and trans-[PdCl2(DEA)2]/[DEA][HAc], used in the model reaction of methyl methacrylate with iodobenzene, 4-iodoanisole, and bromobenzene, provide homogeneous catalysis, good regioselectivity and excellent stereoselectivity. The major product of the regioselective reaction is internal olefin. In all examined cases the only stereoisomer of the internal olefin methyl 3-phenyl-2-methylpropenoate is the E-isomer, whereas the only stereoisomer of the double arylated reaction product methyl 2-benzyl-3-phenylpropenoate is the Z-isomer. A DFT study, which investigates mechanistic aspects of migratory insertion, β-hydride elimination and reductive elimination of this phosphine-free Heck reaction, is in agreement with our experimental findings.

Development of Efficient Catalytic Arylation of Aldehydes with Thioether-Imidazolinium Carbene Ligands

Effective methods of ligand design have been highly sought due to the significant roles of ligands in controlling metal catalyses. In particular, easy-to-handle ligands to realize high reaction efficacy, substrate tolerance, and environmental friendliness are desirable. Novel bidentate ligands containing N-heterocyclic carbene and thioether moieties were developed based on findings of hemilabile coordination, whose precursors were crystalline solids stable enough to handle and store in the air. The thioether-imidazolinium carbene ligand successfully brought out high catalyst performance of palladium in the catalytic arylation of aldehydes with organoboron reagents, which tolerated a diverse range of substrates including poorly reactive, sterically hindered, and heterocyclic compounds. This process was applied to gram-scale synthesis using only water as solvent with high efficiency and also achieved the effective one-pot synthesis of 3-arylphthalides known as useful biologically active agents and important synthetic intermediates for naturally occurring compounds.

Autocatalysis for C–H Bond Activation by Ruthenium(II) Complexes in Catalytic Arylation of Functional Arenes

Kinetic data for the C-H bond activation of 2-phenylpyridine by Ru(II)(carboxylate)(2)(p-cymene) I (acetate) and I' (pivalate) are available for the first time. They reveal an irreversible autocatalytic process catalyzed by the coproduct HOAc or HOPiv (acetonitrile, 27 °C). The overall reaction is indeed accelerated by the carboxylic acid coproduct and water. It is retarded by a base, in agreement with an autocatalytic process induced by HOAc or HOPiv that favors the dissociation of one carboxylate ligand from I and I' and consequently the ensuing complexation of 2-phenylpyridine (2-PhPy). The C-H bond activation initially delivers Ru(O(2)CR)(o-C(6)H(4)-Py)(p-cymene) A or A', containing one carboxylate ligand (OAc or OPiv, respectively). The overall reaction is accelerated by added acetates. Consequently, C-H bond activation (faster for acetate I than for pivalate I') proceeds via an intermolecular deprotonation of the C-H bond of the ligated 2-PhPy by the acetate or pivalate anion released from I or I', respectively. The 18e complexes A and A' easily dissociate, by displacement of the carboxylate by the solvent (also favored by the carboxylic acid), to give the same cationic complex B(+) {[Ru(o-C(6)H(4)-Py)(p-cymene)(MeCN)](+)}. Complex B(+) is reactive toward oxidative addition of phenyl iodide, leading to the diphenylated 2-pyridylbenzene.

Highly Dispersed Palladium–Polypyrrole Nanocomposites: In‐Water Synthesis and Application for Catalytic Arylation of Heteroaromatics by Direct C–H Bond Activation

AbstractPd@PPy hybrid catalytic materials are synthesized in water via redox polymerization reaction of pyrrole with [Pd(NH3)4Cl2]. The nanocomposites formed are composed of highly dispersed palladium particles which are either zerovalent or easily reducible, and are embedded in spherical polypyrrole globules. A unique combination of high palladium dispersion (NP size: 2.4 nm) and elevated palladium content (35 wt%) is obtained. The components of these novel nanocomposites are characterized by means of FTIR, XPS, XRD, SEM, and TEM microscopy techniques. The process of formation in solution is also monitored using UV‐visible and DLS techniques. The application of these novel hybrid nanomaterials in the palladium‐catalyzed direct arylation of heteroaromatics is reported. High efficiency in C–C bond formation is obtained using these materials. Furans and thiophenes are arylated by using bromoarenes. Pd@PPy nanocomposites can efficiently couple n‐butyl furan and n‐butyl thiophene with bromobenzene and bromoquinoline, as well as with activated or deactivated electron‐poor and electron‐rich functionalized bromoarenes. Thus, a clean reaction process is developed that combines the absence of organic ligand in catalytic reactions and easy recovery of Pd@PPy nanocomposite via simple filtration. Preliminary kinetic and post‐catalysis studies suggest a molecular or colloidal soluble active species. These very active species are efficiently delivered by the nanocomposites and susceptible to a surprisingly uniform back redeposition within the polypyrrole support.

ChemInform Abstract: Palladium‐Imidazolinium Carbene‐Catalyzed Arylation of Aldehydes with Arylboronic Acids in Water.

Abstract The catalytic arylation of aldehydes with arylboronic acids in only water was found to be achieved using the palladium/thioether-imidazolinium chloride system in good to excellent yields. This catalytic process showed high tolerance for a broad range of substrates, giving a variety of carbinol derivatives with 2.0–3.0 mol % of the catalyst.

ChemInform Abstract: Catalytic Asymmetric Arylation of N-Substituted 2-Pyrrolines with Aryl Triflates.

Abstract Catalytic asymmetric arylation of 1-(alkoxycarbonyl-2-pyrrolines ( 4 ) with aryl triflates ( 1 ) in benzene in the presence of a base and a palladium catalyst, prepared in situ by mixing Pd(OAc) 2 and ( R )-BINAP, gives optically active ( R -1-(alkoxycarbonyl-5-aryl-2-pyrrolines ( 5 ) of up to 83% ee, together with the regioisomers 1-(alkoxycarbonyl)-5-aryl-3-pyrrolines ( 6 ).

Palladium-imidazolinium carbene-catalyzed arylation of aldehydes with arylboronic acids in water

The catalytic arylation of aldehydes with arylboronic acids in only water was found to be achieved using the palladium/thioether-imidazolinium chloride system in good to excellent yields. This catalytic process showed high tolerance for a broad range of substrates, giving a variety of carbinol derivatives with 2.0–3.0 mol % of the catalyst.

Catalytic arylation and alkylation of phenol with components of the 130–170°C fraction of pyrolysis products

The results of phenol aralkylation with components of the 130–170°C fraction of pyrolysis products on zeolite impregnated with orthophosphoric acid in a flow reactor are presented. The optimal conditions of p-aralkylphenol synthesis have been found. Under the optimal conditions, the yield of the desired aralkylphenol was 53.6% of the theoretical value and the selectivity was 95.5%. A p-aralkylphenolamine resin was synthesized on the basis of p-aralkylphenol and hexamethylenetetramine and was tested as an antioxidant for M-8 motor oil at high temperatures.

Mechanism of Meerwein arylation of furan derivatives

Catalytic arylation of furan-2-carbaldehyde with arenediazonium salts was studied. The yields of 5-arylfuran-2-carbaldehydes were found to depend on the solvent, catalyst, and anion in the arenediazonium salt. Redox catalysis and generation of aryl radicals are not sufficient conditions for the reaction to occur. The reaction is successful only under conditions ensuring formation of complex intermediates. A mechanism involving two Cu2+ ↔ Cu+ catalytic series and generation of furan-2-carbaldehyde was proposed.

ChemInform Abstract: Catalytic Arylation and Vinylation Reactions Directed by Anionic Oxygen Functions via Cleavage of C—H and C—C Bonds

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