Regioselectivity-switchable hydroarylation of styrenes

Cobalt-phosphine and cobalt-carbene catalysts have been developed for the hydroarylation of styrenes via chelation-assisted C-H bond activation, to afford branched and linear addition products, respectively, in a highly regioselective fashion. Deuterium-labeling experiments suggested a mechanism involving reversible C-H bond cleavage and olefin insertion steps and reductive elimination as the rate- and regioselectivity-determining step.     

Efficient metal-catalyzed hydroarylation of styrenes

[reaction: see text] A highly efficient metal-catalyzed hydroarylation of various styrenes has been developed. This new bismuth-catalyzed C-H functionalization provides straightforward access to a series of valuable 1,1-diarylalkane products.     

Regioselective allylic alkylation and etherification catalyzed by in situ generated N-heterocyclic carbene ruthenium complexes

Benzimidazolium halides are used for the first time as ligand precursors in ruthenium-catalyzed substitution of allylic carbonates and chlorides by carbon nucleophiles and phenols, respectively. After generation of diaminocarbene species upon deprotonation by tBuOK, their association with [Cp*Ru(MeCN)₃]PF₆ induces a very high regioselectivity in favor of the branched isomers when cinnamyl derivatives are used as starting substrates. They also provide good regioselectivities for the allylation of phenols by unsymmetrical aliphatic allylic substrates such as 3-chloro-4-phenylbut-1-ene, and thus provide a straightforward access to new allylic phenyl ethers.     

Asymmetric palladium-catalyzed hydroarylation of styrenes and dienes

Alkenes are desirable and highly versatile starting materials for organic transformations, and well-known substrates for palladium catalysis. Typically, these reactions result in the formation of a new alkene product via β-hydride elimination. In contrast to this scenario, our laboratory has been involved in the development of alkene hydro- and difunctionalization reactions, where β-hydride elimination can be controlled. We report herein the development of an asymmetric palladium-catalyzed hydroarylation, which yields diarylmethine products in up to 75% ee. Interestingly, a linear free energy relationship is observed between the steric bulk of the ligand within a certain range and the ee of the reaction.     

Highly efficient iodine-catalyzed hydroarylation of arenes with styrenes

Iodine mediates the hydroarylation of styrenes with arenes and heteroarenes to afford 1,1-diarylalkanes in good to high yields. Details regarding the substrate scope and selectivity of this hydroarylation reaction are discussed.     

A convenient FeCl3-catalyzed hydroarylation of styrenes

[reaction: see text] 1,1-Diarylalkanes are easily synthesized by CH-functionalization reactions of electron-rich arenes and heteroarenes with styrenes in the presence of FeCl(3) as catalyst.     

Norbornene hydroarylation catalyzed by ferrocene palladacycle complexes

Two ferrocene derivatives containing palladacycles with bidentate (C,N) and tridentate (C,N,N) ligands were successfully used as catalysts for the hydroarylation of norbornene.     

Esterification of carboxylic acids catalyzed by in situ generated tetraalkylammonium fluorides

Esterification of carboxylic acids with alkyl halides can be efficiently catalyzed by tetrabutylammonium fluoride (TBAF) generated in situ from tetrabutylammonium hydrogensulfate (TBAHSO₄) and KF·2H₂O in THF. The general applicability and the characteristic feature of this approach has been amply demonstrated.     

Silylation of silanols with vinylsilanes catalyzed by a ruthenium complex

A new ruthenium complex-catalyzed O-silylation of silanols with vinylsilanes leading to siloxane bond formation with the evolution of ethylene is described. A maximum conversion of silanol is reached using an excess of vinylsilane to also yield the product of the homo-coupling of the latter. Under the optimum conditions, when vinylsilane with at least one ethoxy substituent is used, the reaction gives exclusively unsymmetrical siloxanes.     

Highly efficient epoxidation of cyclic alkenes catalyzed by ruthenium complex

The epoxidation of cyclic alkenes with molecular oxygen was efficiently completed in excellent epoxide yield using a novel ruthenium complex as catalyst under mild reaction conditions.     

Regioselective hydrostannation of activated alkynes catalyzed by in situ generated copper hydride

The hydrostannation of activated alkynes proceed in good yields and high regioselectivities catalyzed by CuCl, in the presence of potassium tert-butoxide, triphenylphosphine, and tributylstannane, by generating copper hydride in situ.     

Highly stable ECL active films formed by the electrografting of a diazotized ruthenium complex generated in situ from the amine

The electrodeposition of the electrochemiluminescent (ECL) ruthenium complex, bis(2,2'-bipyridyl)(4'-(4-aminophenyl)-2,2'-bipyridyl)ruthenium(II), [Ru(bpy)(2)(apb)](2+), via the in situ formation of a diazonium species from aqueous media is reported. Surface characterization undertaken using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) determined that the layer is bound to the substrate via azo bonding. The layer displays good ECL activity and is stable over a long period of time. The excellent potential of this system for ECL sensing applications is demonstrated using the well-known ECL coreactant 2-(dibutylamino)ethanol (DBAE) as a model analyte, which can be detected to a level of 10 nM with a linear range between 10(-8) and 10(-4) M.     

Aerobic oxidative dehydrogenation of benzylamines catalyzed by a cyclometalated ruthenium complex

The ruthenium(III) complex bearing phenylpyridine as a cyclometalated ligand serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzylamines to the corresponding benzonitriles under mild conditions.     

Unexpected reaction of dimethyl acetylenedicarboxylate with in situ generated arylketenes catalyzed by 1-methylimidazole

[reaction: see text]. An unexpected 1-methylimidazole-catalyzed reaction of dimethyl acetylenedicarboxylate (DMAD) with in situ generated arylketenes leading to the synthesis of dimethyl 2-arylidenesuccinates under mild conditions is described. A plausible mechanism has been proposed.     

Photoredox-copper catalyzed Meerwein cyanoarylation of styrenes

A new procedure for the cyanoarylation of styrenes with arenediazonium salts and Bu₄NCN employs double catalytic system Eosyn Y/Cu(OAc)₂ under the irradiation with green light (530 nm). In the case of diazonium salts bearing electron withdrawing substituents, the products are formed in 40–65% yields. The relative thiocyanatoarylation proceeds only in the presence of photocatalyst, but the Cu(OAc)₂ additive allows for the product yield improvement     

Photostimulated oxidation of water catalyzed by a tetranuclear ruthenium complex with lithium countercations

Photostimulated oxidation of water by potassium persulfate in the presence of photosensitizer bpy₃RuCl₂ ? 6H₂O and ruthenium catalyst Li₁₀[{Ru₄(μ-O)₄(μ-OH)₂(H₂O)₄} ? (γ-SiW₁₀O₃₆)₂] ? 10H₂O has been studied. It has been shown that the quantum yield of O₂ (0.29) is much higher than the quantum yield in a similar photocatalytic system with rubidium countercations (0.09).     

NH insertion reactions catalyzed by reusable water-soluble ruthenium(II)-hm-phenyloxazoline complex

A water-soluble Ru(II)-hm-pheox complex was efficiently catalyzed NH insertion of EDA with a broad class of amine derivatives in water/ether biphasic medium to deliver the biologically active precursors α-aminoester products with excellent yields (up to >99%). The products were separated by decantation and the catalyst was washed and reused several times (at least 8 times) without any specific loss of its catalytic activity. The plausible mechanism of the reaction was explained. Additionally, In case of ethylene diamine, the NH insertion product could be transformed to biological active piperazinone compound in high yield. The asymmetric version of this catalytic reaction is under investigation.