Palladacycle-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylic Acids with Aryl Chlorides under Air

An Efficient and Sustainable Approach to Decarboxylative Cross-Coupling Using Silica Coated Magnetic Copper Nanocatalyst for the Synthesis of Internal Alkynes

A highly efficient magnetically separable copper nanocatalyst has been developed for decarboxylative cross-coupling reaction for the alkynylation of haloarenes using alkynoic acid as a reaction partner. The chemical nature, morphology, size, and magnetic properties of the prepared nanocatalyst were studied by SEM, TEM, EDS, FT-IR, VSM, and ICP techniques. Remarkably, this catalyst represents the first successful copper based heterogeneous system for this type of coupling that provides a low-cost, stable, and environmentally friendly magnetically recoverable entity that can be re-used for seven consecutive runs without appreciable loss in its catalytic performance.

Silver-Catalyzed Decarboxylative Allylation of Difluoroarylacetic Acids with Allyl Sulfones in Water

A practical silver-catalyzed decarboxylative allylation of α,α-difluoroarylacetic acids with allyl sulfones is described, which provides a variety of β,β-difluorinated alkenes in good yields. Notably, the reaction proceeds smoothly in water with good functional group tolerance. The practicality and synthetic value of this process was demonstrated by scaled-up experiment and elaboration of the products via reduction or Heck reaction. Primary mechanism investigations suggest that a radical process might be involved.

Palladium-catalyzed decarboxylative gem-selective addition of alkynoic acids to terminal alkynes

Alkynoic acids added to terminal alkynes to give gem-1,3-enynes with high selectivity and good yields. In addition, the reaction of alkynoic acids with propiolic acid provided the corresponding gem-1,3-enynes via double decarboxylation.

Pd-Catalyzed decarboxylative alkynylation of alkynyl carboxylic acids with arylsulfonyl hydrazides via a desulfinative process

The decarboxylative alkynylation of alkynyl carboxylic acids and arylsulfonyl hydrazides by desulfinative coupling could provide aryl alkynes in satisfactory yields by either judiciously selecting palladium catalysts or modulating phosphine ligands under mild conditions.

Facile Fabrication of Ordered Component-Tunable Heterobimetallic Self-Assembly Nanosheet for Catalyzing "Click" Reaction

How to maximize the number of desirable active sites on the surface of the catalyst and minimize the number of sites promoting undesirable side reactions is currently an important research topic. In this study, a new way based on the synergism to achieve the successful fabrication of an ordered heterobimetallic self-assembled monolayer (denoted as BMSAM) with a controlled composition and an excellent orientation of metals in the monolayer was developed. BMSAM consisting of phenanthroline and Schiff-base groups was prepared, and its novel heterobimetallic (Cu and Pd) self-assembled monolayer anchored in silicon (denoted as Si-Fmp-Cu-Pd BMSAM) with a controlled composition and a fixed position was fabricated and characterized by UV, cyclic voltammetry, Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and water-drop contact angle (WDCA) analyses. The effects of Si-Fmp-Cu-Pd BMSAM on its catalytic properties were also systematically investigated using "click" reaction as a template by WDCA, XPS, SEM, XRD, ICP-AES and in situ Fourier transform infrared analyses in a heterogeneous system. The results showed that the excellent catalytic characteristic could be attributed to the partial (ordered or proper distance) isolation of active sites displaying high densities of specific atomic ensembles. The catalytic reaction mechanism of the click reaction interpreted that the catalytic process mainly occurred on the surface of the monolayer, internal active site (Pd) and rationalized that the Cu(I) species and Pd(0) reduced from the Cu(II) and Pd(II) catalyst were active species, which had a proper distance between two different metals. The cuprate-triazole intermediate and the palladium intermediate, whose production is the key step, should lie in a proper position between the copper and active palladium sites, with which the reaction rate of transmetalation would be improved to increase the amount of the undesired Sonogashira coupling product.

Palladium-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylic Acids with Aryl Tosylates

Decarboxylative coupling reactions of alkynyl carboxylic acids with aryl tosylates were developed in the presence of a palladium catalyst. Among the commercially available phosphine ligands, only 1-dicyclohexylphosphino-2-(di-tert-butylphosphino-ethyl)ferrocene (CyPF-tBu) showed good reactivity. The reaction took place smoothly and gave the decarboxylative coupled products in moderate to good yields. This demonstrates the excellent functional group tolerance toward alkyl, alkoxy, fluoro, thiophenyl, ester, and ketone groups. In addition, alkyl-substituted propiolic acids, such as octynoic and hexynoic acids, were coupled with phenyl tosylate to provide the desired products. We found that the electronic properties of the substituents on the phenyl ring in arylpropiolic acids are an important factor. The order of reactivity was found to be aryl iodide > aryl bromide > aryl tosylate > aryl chloride. However, aryl chloride-bearing electron-withdrawing groups showed higher reactivity than those bearing aryl tosylates.

Transformation of Carbonyl Compounds into Homologous Alkynes under Neutral Conditions: Fragmentation of Tetrazoles Derived from Cyanophosphates

Cyanophosphates (CPs) can be easily prepared from either ketones or aldehydes, and their reaction with NaN₃-Et₃N·HCl results in the formation of azidotetrazoles. Under microwave irradiation, successive fragmentation of the azidotetrazoles generates alkylidene carbenes that undergo [1,2]-rearrangement and are transformed into homologous alkynes. Treatment of ketone-derived CPs with TMSN₃ and Bu₂SnO as catalyst in toluene at reflux directly yields the corresponding internal alkynes, whereas the reaction of aldehyde-derived CPs with NaN₃-Et₃N·HCl in THF at reflux or TMSN₃-Bu₂SnO (cat.) in toluene at reflux provides homologous terminal alkynes in good yields. These reactions take place under neutral conditions and can be successfully extended to obtain alkynes that are not usually accessible from the corresponding carbonyl compounds by the Ohira-Bestmann or Shioiri procedures, which require basic conditions.

Supported palladium nanoparticles-catalyzed decarboxylative coupling approaches to aryl alkynes, indoles and pyrrolines synthesis

The polystyrene supported palladium (Pd@PS) nanoparticles catalyzed decarboxylative coupling of arylhalides and alkynyl carboxylic acids was developed for the synthesis of diaryl alkynes, indoles and pyrrolines.

Decarboxylative/Sonogashira-type cross-coupling using PdCl2(Cy*Phine)2

Expedient protocol to access a wide range of internal alkynes and symmetrical di(heteroaryl)alkynes via tandem decarboxylative–Sonogashira cross-coupling.

Position of Substitution: A Facile Way to Tune the Spectroscopic Properties of Dimethylamino-Substituted Arylene-Ethynylenes

A series of dimethylamino-substituted arylene-ethynylenes were synthesised by Sonogashira coupling reactions and characterised by the methods of 1H, 13C NMR, UV-Vis, fluorescence, HRMS and theoretical calculations. Effects on spectroscopic properties caused by the different positions of the dimethylamino group in arylene-ethynylenes were studied and discussed. The shortest absorption maximum, the largest Stokes shift and the highest fluorescence efficiency were observed for arylene-ethynylenes with a dimethylamino group present in the ortho-position.

Efficient Catalytic Sonogashira Reaction Catalysed by Modified Fibre-Palladium(II) Complex in Air

A hydroxylamine modified polypropylene fibre [Pd(II)-AOFs] was synthesised and used to catalyse the Sonogashira reaction between phenylacetylene and iodobenzene. The results showed that highly efficient catalytic activity can be achieved for the cross-coupling reaction. More importantly, the reaction conditions are moderate and do not require inert gas protection. The catalyst could be readily extracted by simple operations and conveniently recycled four times without an obviously significant decrease in activity.

Copper-catalyzed direct decarboxylative hydrosulfonylation of aryl propiolic acids with sulfonylhydrazides leading to vinylsulfones

A simple and facile protocol for (E)-vinylsulfones was developed using inexpensive propiolic acids or terminal alkynes as new alkene sources.

An electrochemically polymerized and assembled cyclopalladated bi-thiophene imine for catalyzing coupling reactions: a modern strategy to enhance catalytic activity

The catalytic activity and recyclability of thiophene imine as a catalyst for coupling reactions is enhanced using the LB-ECP-SA method.

Copper-catalyzed ring expansion of 2-aminobenzothiazoles with alkynyl carboxylic acids to 1,4-benzothiazines

A novel copper-catalyzed ring expansion of 2-aminobenzothiazoles to 1,4-benzothiazines is described.

Practical synthesis of aryl-2-methyl-3-butyn-2-ols from aryl bromides via conventional and decarboxylative copper-free Sonogashira coupling reactions

Two efficient protocols for the palladium-catalyzed synthesis of aryl-2-methyl-3-butyn-2-ols from aryl bromides in the absence of copper were developed. A simple catalytic system consisting of Pd(OAc)₂ and P(p-tol)₃ using DBU as the base and THF as the solvent was found to be highly effective for the coupling reaction of 2-methyl-3-butyn-2-ol (4) with a wide range of aryl bromides in good to excellent yields. Analogously, the synthesis of aryl-2-methyl-3-butyn-2-ols was performed also through the decarboxylative coupling reaction of 4-hydroxy-4-methyl-2-pentynoic acid with aryl bromides, using a catalyst containing Pd(OAc)₂ in combination with SPhos or XPhos in the presence of tetra-n-butylammonium fluoride (TBAF) as the base and THF as the solvent. Therefore, new efficient approaches to the synthesis of terminal acetylenes from widely available aryl bromides rather than expensive iodides and using 4 or propiolic acid rather than TMS-acetylene as inexpensive alkyne sources are described.

Synthesis of 2,5-diaryl-substituted thiophenes as helical mimetics: towards the modulation of islet amyloid polypeptide (IAPP) amyloid fibril formation and cytotoxicity

A range of 2,5-diarylated thiophenes were synthesised as small molecule mimetics of the α-helix to modulate the amyloidogenesis and cytotoxic effect of islet amyloid polypeptide (IAPP). 3-Substituted thiophene-2-carboxylic acids were used as key intermediates and functionalised by palladium decarboxylative cross-coupling and direct C-H activation successively with overall yields ranging from 23 to 95 %. The effect of the ligands on IAPP amyloid fibril formation was evaluated with the thioflavin T (ThT) fluorescence-based assay. Furthermore, the capacity of these compounds to inhibit the cytotoxic effect of IAPP was assessed using β-pancreatic cells.

A general catalyst for Suzuki–Miyaura and Sonogashira reactions of aryl and heteroaryl chlorides in water

An air-stable sulfonated indenyl phosphine/Pd-catalyst system was used in Suzuki–Miyaura and Sonogashira coupling reactions in water.

Synthesis of diarylalkynes via tandem Sonogashira/decarboxylative reaction of aryl chlorides with propiolic acid

A tandem Sonogashira/decarboxylative coupling of aryl chlorides with propiolic acid for one-pot synthesis of diarylalkynes was developed.