Solvent-Controlled Highly Selective Bis- and Monoallylation of Active Methylene Compounds by Allyl Acetate with Palladium(0) Nanoparticle

Unprecedented C-C Bond Formation via Ipso Nucleophilic Substitution of 2,4-Dinitrobenzene Sulfonic Acid with Active Methylene Compounds

The sulfonic acid functionalization of sufficiently electron-deficient benzene sulfonic acids undergoes ipso nucleophilic substitution with various active methylene compounds, leading to new C-C bond formation. Good to excellent yields are obtained under mild conditions without transition-metal (Pd or Cu) catalyst, PTC, and ligand. No solid waste is generated. It is a highly effective strategy for incorporating various active methylene compounds into the o-nitro-substituted benzene ring. This method has been applied not only for synthesizing APIs but also in materials chemistry. It shows a novel route for creating heavily crowded all-carbon quaternary centers. Carbon-carbon bond formation by substituting a sulfonic acid group was unknown.

Au-Catalyzed Formal Allylation of Diazo(thio)oxindoles: Application to Tandem Asymmetric Synthesis of Quaternary Stereocenters

We report an efficient Au(I)-catalyzed formal allylation of diazo(thio)oxindoles using allyltrimethylsilane to give 3-allyl (thio)oxindoles, which are difficult to access by using traditional alkylation methods under basic conditions. The approach enables a highly stereoselective synthesis of quaternary (thio)oxindoles via a formal allylation-asymmetric Michael addition sequence. These adducts are versatile synthons for spirocyclic (thio)oxindoles. Initial biological studies reveal that chiral thiooxindoles show promising antiproliferation activity that is better than that of the corresponding oxindoles.

Boron-catalyzed dehydrative allylation of 1,3-diketones and β-ketone esters with 1,3-diarylallyl alcohols in water

A metal-free catalytic allylation with atom economy and green environment friendly was developed. Allylic alcohols could be directly dehydrated in water by B(C6F5)3, without using any base additives. The reaction can afford the corresponding monoallylated product in moderate to high yield and has been performed on a gram-scale, and a quaternary carbon center can be constructed for the active methine compounds of 1,3-diketones or β-ketone esters in this process. The product can be further converted, such as the synthesis of tetra-substituted pyrazole compounds, or 1,4-dienes and functionalized dihydropyrans.

Monoallylation and benzylation of dicarbonyl compounds with alcohols catalysed by a cationic cobalt(iii) compound

Monoallylation and monoalkylation of diketones and β-keto esters with allylic and benzylic alcohols catalysed by [Cp*Co(CH3CN)3][SbF6]2 (I) are reported. The method does not require any additive and affords regioselective products. The mechanistic investigations were done by in situ 1H NMR spectroscopy as well as control experiments. It has been shown that reactions proceed via η3-allyl complex formation or ally ether intermediate. The alkylation takes place via only ether intermediate. The resulting allylated and alkylated products have been used for the synthesis of eleven new trisubstituted pyrazoles and one pyrazolone.

Highly efficient Tsuji–Trost allylation in water catalyzed by Pd-nanoparticles

Palladium nanoparticles stabilized by poly(vinylpyrrolidone) catalyze Tsuji–Trost allylations in water with very high turnover numbers.

Rational synthesis of Pd nanoparticle-embedded reduced graphene oxide frameworks with enhanced selective catalysis in water

A three-dimensional (3D) Pd-reduced graphene oxide framework (Pd-rGOF) with hierarchical macro- and mesoporous structures has been developed via covalence- and coordination-assisted self-assembly approach. In this facile fabrication process, GO was first cross-linked with triethylene tetramine (TETA) to form 3D GOF, in which well-dispersed and ultrasmall Pd nanoparticles (NPs) in situ grew and embedded the framework. The obtained nanopores, 3D Pd-rGOF, can act as nanoreactors to help the reaction substrates thoroughly contact with the surface of Pd NPs, thereby exhibiting high activity and selectivity toward the Tsuji-Trost reaction in water, with 99% conversion and selectivity for most substrates. Moreover, the 3D Pd-rGOF catalyst can be reused more than ten times without significant loss of activity, rendering this catalyst long-term stability. The abovementioned observations make the rGOF a universal platform to coordinate other noble metal ions (NM) to construct desired NM-rGOF nanocatalysts with improved activity, selectivity, and durability that can be used in a broad range of practical applications.

A Pd–bisphosphine complex and organic functionalities immobilized on the same SiO2 surface: detailed characterization and its use as an efficient catalyst for allylation

A Pd–bisphosphine complex and several organic functionalities were immobilized on the same SiO₂ surface.

Highly selective palladium-benzothiazole carbene-catalyzed allylation of active methylene compounds under neutral conditions

The Pd–benzothiazol-2-ylidene complex I was found to be a chemoselective catalyst for the Tsuji–Trost allylation of active methylene compounds carried out under neutral conditions and using carbonates as allylating agents. The proposed protocol consists in a simplified procedure adopting an in situ prepared catalyst from Pd₂dba₃ and 3-methylbenzothiazolium salt V as precursors. A comparison of the performance of benzothiazole carbene with phosphanes and an analogous imidazolium carbene ligand is also proposed.

Peptide-Nanofiber-Supported Palladium Nanoparticles as an Efficient Catalyst for the Removal of N-Terminus Protecting Groups

Sonication-induced tryptophan- and tyrosine-based peptide bolaamphiphile nanofibers have been used to synthesize and stabilize Pd nanoparticles under physiological conditions. The peptide bolaamphiphile self-assembly process has been thoroughly studied by using several spectroscopic and microscopic techniques. The stiffness of the soft hydrogel matrix was measured by an oscillatory rheological experiment. FTIR and circular dichroism (CD) experiments revealed a hydrogen-bonded β-sheet conformation of peptide bolaamphiphile molecules in a gel-phase medium. The π-π stacking interactions also played a crucial role in the self-assembly process, which was confirmed by fluorescence spectroscopy. Electron (SEM and TEM) and atomic force microscopy (AFM) studies showed that the peptide bolaamphiphile molecules self-assemble into nanofibrillar structures. Pd nanoparticles were synthesized in the hydrogel matrix in which redox-active tryptophan and tyrosine residues reduce the metal ions to metal nanoparticles. The size of the Pd nanoparticles are in the range of 3-9 nm, and are stabilized by peptide nanofibers. The peptide-nanofiber-supported Pd nanoparticles have shown effective catalytic activity for the removal of N-terminus protecting groups of amino acids and peptides.

Metal nanoparticles as efficient catalysts for organic reactions

Pd(0) nanoparticles have been demonstrated to be very efficient catalysts for C–C bond-forming reactions. These include coupling of vicinal-diiodoalkenes and acrylic esters and nitriles leading to the stereoselective synthesis of 2-alkene-4-yn-esters and nitriles, allylation of active methylene compounds by allyl acetate, and Hiyama cross-coupling of aryliodides with arylsilanes. Cu(0) nanoparticles catalyze aryl-sulfur bond formation, accomplishing the synthesis of functionalized aryl sulfides and aryl- and vinyl dithiocarbamates. Cu nanoparticles have also been used for the chemoselective reduction of aromatic nitro compounds.

Scope and Mechanistic Investigations on the Solvent-Controlled Regio- and Stereoselective Formation of Enol Esters from the Ruthenium-Catalyzed Coupling Reaction of Terminal Alkynes and Carboxylic Acids

The ruthenium-hydride complex (PCy(3))(2)(CO)RuHCl was found to be a highly effective catalyst for the alkyne-to-carboxylic acid coupling reaction to give synthetically useful enol ester products. Strong solvent effect was observed for the ruthenium catalyst in modulating the activity and selectivity; the coupling reaction in CH(2)Cl(2) led to the regioselective formation of gem-enol ester products, while the stereoselective formation of (Z)-enol esters was obtained in THF. The coupling reaction was found to be strongly inhibited by PCy(3). The coupling reaction of both PhCO(2)H/PhC identical withCD and PhCO(2)D/PhC identical withCH led to the extensive deuterium incorporation on the vinyl positions of the enol ester products. An opposite Hammett value was observed when the correlation of a series of para-substituted p-X-C(6)H(4)CO(2)H (X = OMe, CH(3), H, CF(3), CN) with phenylacetylene was examined in CDCl(3) (rho = +0.30) and THF (rho = -0.68). Catalytically relevant Ru-carboxylate and -vinylidene-carboxylate complexes, (PCy(3))(2)(CO)(Cl)Ru(kappa(2)-O(2)CC(6)H(4)-p-OMe) and (PCy(3))(2)(CO)(Cl)RuC(=CHPh)O(2)CC(6)H(4)-p-OMe, were isolated, and the structure of both complexes was completely established by X-ray crystallography. A detailed mechanism of the coupling reaction involving a rate-limiting C-O bond formation step was proposed on the basis of these kinetic and structural studies. The regioselective formation of the gem-enol ester products in CH(2)Cl(2) was rationalized by a direct migratory insertion of the terminal alkyne via a Ru-carboxylate species, whereas the stereoselective formation of (Z)-enol ester products in THF was explained by invoking a Ru-vinylidene species.