Pd-catalyzed coupling reaction of acid chlorides with terminal alkynes using 1-(2-pyridylethynyl)-2-(2-thienylethynyl)benzene ligand

Platform for the Immobilizing of Ultrasmall Pd Clusters for Carbonylation: In Situ Self-Templating Fabrication of ZIF-8 on ZnO

Incorporating metal clusters into the confined cavities of metal-organic frameworks (MOFs) to form MOF-supported catalysts has attracted considerable research interest with regard to carbonylation reactions. Herein, a self-templating method is used to prepare the zinc oxide (ZnO)-supported core-shell catalyst ZnO@Pd/ZIF-8. This facile strategy controls the growth of metal sources on the ZIF-8 shell layer and avoids the metal diffusion or aggregation problems of the conventional synthesis method. The characteristics of the catalysts show that the palladium (Pd) clusters are highly dispersed with an average particle size of ≈1.2 nm, making them excellent candidates as a catalyst for carbonylation under mild conditions. The optimal catalyst (1.25-ZnO@Pd/ZIF-8) exhibits excellent activity in synthesizing α, β-alkynyl ketones under 1 atm of carbon monooxide (CO), and the conversion rate of 1, 3-diphenylprop-2-yn-1-one is 3.09 and 3.87 times more than those of Pd/ZIF-8 and Pd2+, respectively, for the first 2 h. Moreover, the 1.25-ZnO@Pd/ZIF-8 is recyclable, showing negligible metal leaching, and, under the conditions used in this investigation, can be reused at least five times without considerable loss in its catalytic efficiency. This protocol can also be applied with other nucleophile reagents to synthesize esters, amides, and acid products.

Are bis(pyridine)iodine(I) complexes applicable for asymmetric halogenation?

Enantiopure halogenated molecules are of tremendous importance as synthetic intermediates in the construction of pharmaceuticals, fragrances, flavours, natural products, pesticides, and functional materials. Enantioselective halofunctionalizations remain poorly understood and generally applicable procedures are lacking. The applicability of chiral trans-chelating bis(pyridine)iodine(i) complexes in the development of substrate independent, catalytic enantioselective halofunctionalization has been explored herein. Six novel chiral bidentate pyridine donor ligands have been designed, routes for their synthesis developed and their [N–I–N]⁺-type halogen bond complexes studied by ¹⁵N NMR and DFT. The chiral complexes encompassing a halogen bond stabilized iodenium ion are shown to be capable of efficient iodenium transfer to alkenes; however, without enantioselectivity. The lack of stereoselectivity is shown to originate from the availability of multiple ligand conformations of comparable energies and an insufficient steric influence by the chiral ligand. Substrate preorganization by the chiral catalyst appears a necessity for enantioselective halofunctionalization.

The enantioselectivity of the iodine(i) transfer process from chiral bis(pyridine)iodine(i) complexes to alkenes is explored.

Straightforward Stereoselective Synthesis of Seven-Membered Oxa-Bridged Rings through In Situ Generated Cycloheptenol Derivatives

An iodine-mediated stereoselective synthesis of seven-membered oxa-bridged rings via in situ generated cycloheptenols was reported. This process was realized through the combination of C-C σ-bond cleavage and C-O bond-forming reactions in a one-pot fashion from simple and easily accessible raw materials. The formation of carbon radicals initiated by I₂ was the key to the reaction.

Investigation of the Selectivity of the Palladium-Catalyzed Aroylation and Arylation of Stannyl Glycals with Aroyl Chlorides

The selectivity of the palladium-catalyzed aroylation and arylation of 1-tributylstannyl glycals with aroyl chlorides was investigated. The selectivity was controlled by the palladium catalyst, and high selectivity was achieved via ligand modification of the palladium catalyst. The reaction catalyzed by Pd(OAc)2 provided aroyl C-glycals with high selectivity, whereas the reaction catalyzed by Pd(PPh3)4 produced aryl C-glycals with diminished selectivity. The scope and limitation of the selectivity in this reaction are discussed.

Synthesis of Alkynyl Ketones by Sonogashira Cross-Coupling of Acyl Chlorides with Terminal Alkynes Mediated by Palladium Catalysts Deposited over Donor-Functionalized Silica Gel

Palladium catalysts deposited over silica gel bearing simple amine (≡Si(CH2)3NH2) and composite functional amide pendants equipped with various donor groups in the terminal position (≡Si(CH2)3NHC(O)CH2Y, Y = SMe, NMe2 and PPh2) were prepared and evaluated in Sonogashira-type cross-coupling of acyl chlorides with terminal alkynes to give 1,3-disubstituted prop-2-yn-1-ones. Generally, the catalysts showed good catalytic activity in the reactions of aroyl chlorides with aryl alkynes under relatively mild reaction conditions even without adding a copper co-catalyst. However, their repeated use was compromised by a significant loss of activity after the first catalytic run.

Catalytic Activity of trans-Bis(pyridine)gold Complexes

Gold catalysis has become one of the fastest growing fields in chemistry, providing new organic transformations and offering excellent chemoselectivities under mild reaction conditions. Methodological developments have been driven by wide applicability in the synthesis of complex structures, whereas the mechanistic understanding of Au(III)-mediated processes remains scanty and have become the Achilles’ heel of methodology development. Herein, the systematic investigation of the reactivity of bis(pyridine)-ligated Au(III) complexes is presented, based on NMR spectroscopic, X-ray crystallographic, and DFT data. The electron density of pyridines modulates the catalytic activity of Au(III) complexes in propargyl ester cyclopropanation of styrene. To avoid strain induced by a ligand with a nonoptimal nitrogen–nitrogen distance, bidentate bis(pyridine)–Au(III) complexes convert into dimers. For the first time, bis(pyridine)Au(I) complexes are shown to be catalytically active, with their reactivity being modulated by strain.

Acyl Sonogashira Cross-Coupling: State of the Art and Application to the Synthesis of Heterocyclic Compounds

The acyl Sonogashira reaction represents an extension of Sonogashira cross-coupling to acid chlorides which replace aryl or vinyl halides, while terminal acetylenes are used as coupling partners in both reactions. The introduction of a carbonyl functional group on the alkyne backbone determines a radical change in the reactivity of the products. Indeed, α,β-alkynyl ketones can be easily converted into different heterocyclic compounds depending on the experimental conditions employed. Due to its potential, the acyl Sonogashira reaction has been deeply studied with particular attention to the nature of the catalysts and to the structures of both coupling compounds. Considering these two aspects, in this review, a detailed analysis of the literature data regarding the acyl Sonogashira reaction and its role in the synthesis of several heterocyclic derivatives is reported.

Synthesis of ynones at room temperature catalyzed by copper chloride cryptand complex under solvent free conditions

An air-stable highly efficient reusable CuCl₂-cryptand-[2.2.Benzo] catalyst is reported first time for coupling reaction of terminal alkynes with different acyl chlorides in the presence of triethylamine acting both as base and solvent at room temperature to give the corresponding ynones. Easy-going, short reaction time, cost-effective, palladium-, phosphorus- and solvent-free, high yield and recyclability up to 5^th times make this method green procedure for ynones’ synthesis with wide substrate variety.

One-pot regioselective synthesis of substituted pyrazoles and isoxazoles in PEG-400/water medium by Cu-free nano-Pd catalyzed sequential acyl Sonogashira coupling–intramolecular cyclization

Catalyst efficacy of in situ generated Pd-nanoparticles in the regioselective one-pot synthesis of substituted pyrazoles and isoxazoles via sequential coupling-cyclization methodology in environmentally benign medium is described.

A polysalen based on polyacylamide stabilized palladium nanoparticle catalyst for efficient carbonylative Sonogashira reaction in aqueous media

Pd nanoparticles immobilized on polysalen based on polyacylamide was synthesized and used for carbonylative Sonogashira coupling of aryl iodides with terminal alkynes to produce α,β-alkynyl ketones in aqueous media.

Palladium-catalyzed carbonylative Sonogashira coupling of aryl diazonium salts with formic acid as the CO source: the effect of 1,3-butadiene

An efficient carbonylative cross-coupling of aryl diazonium salts with terminal alkynes using formic acid as the CO source has been developed. And 1,3-butadiene was found to play a crucial role in this transformation.

A facile and rapid route for the synthesis of Cu/Cu2O nanoparticles and their application in the Sonogashira coupling reaction of acyl chlorides with terminal alkynes

This work reports a simple, rapid and efficient protocol for synthesis of Cu/Cu₂O nanoparticles. The prepared Cu/Cu₂O nanoparticles were effectively utilized for Sonogashira coupling reaction of acyl chlorides with terminal alkynes.

A one-pot coupling-addition-cyclocondensation sequence (CACS) to 2-substituted 3-acylpyrroles initiated by a copper-free alkynylation

A novel three-component synthesis of 2-substituted 3-acylpyrroles can be initiated by a copper-free Pd-catalyzed alkynylation in a one-pot fashion. The reaction sequence proceeds under mild reaction conditions and in moderate to good yields with a broad scope of diversity.