Search Results (80)

This work describes the straightforward synthesis of a novel heterogeneous palladium catalyst immobilized on magnetic Janus-type silica particles coated with an amphiphilic ionic liquid (IL) layer. The material was prepared via a one-pot process wherein TEOS (tetraethoxysilane) and a bis(triethoxysilane) IL precursor are combined to form hollow shells. The IL motifs are selectively located on the outer surface of the hollow particles and serve as centers for the immobilization of palladium species on the material’s surface. The outer surface also hosts magnetic nanoparticles in close proximity to the palladium sites. Thanks to the uniform coverage of the surface with the amphiphilic IL functionality, the material exhibits a well-balanced wettability with reaction components of different polarities. The catalyst’s activity was tested in the Sonogashira cross-coupling reaction of terminal acetylenes and iodobenzene derivatives in water as the solvent. The results show that the mixed palladium–iron oxide catalyst exhibits higher activity than materials containing either immobilized palladium or iron oxide alone, suggesting a synergistic effect in this reaction. Additionally, the reaction proceeds well in the absence of expensive organic ligands and commonly employed additives such as copper co-catalysts or phase transfer catalysts. Furthermore, the material was also used in the oxidative Sonogashira coupling reaction of phenylboronic acid and phenylacetylene. The catalyst can be easily separated using an external magnet and can be reused several times. The feasibility of producing diphenylacetylene on a gram scale via the Sonogashira cross-coupling reaction was also investigated. Full article

Oligo(arylene ethynylene)s (OAEs) containing 4,5-(diethynylaryl)-1,2,3-triazoles with 3(OMe) and NR₂ substituents at the 5-position and bis-1,4-dialkoxybenzene moieties as spacers at the 4-position were obtained using the retro-Favorskii reaction as a key step. The most intense fluorescence was observed for OAEs with a trimethoxyphenyl substituent in THF solutions, with a quantum yield of up to 88%. Increasing the solvent polarity had minimal effect on the emission of trimethoxyphenyl substituted derivatives. A notable red shift in emission spectra was observed with increasing solvent polarity for OAEs 10a,g containing para-dimethylaminophenyl group. Their emission spectra in aqueous organic solutions revealed that an increase in water fraction in THF/water mixtures led to a bathochromic shift in emission spectra maxima accompanied by a hypochromic effect. An increase in intensity was observed in aqueous acetonitrile and DMSO. The maximum intensity was observed in DMSO solutions containing 30% water, which is attributed to aggregate-induced emission enhancement. Dynamic light scattering data also confirmed the formation of nanoscale aggregates in aqueous organic mixtures. Full article

A carbon-supported palladium-containing polysiloxane macrocatalyst (Pd-PDMS) was developed for pharmaceutical-grade cross-coupling reactions. The catalyst demonstrates exceptional year-long stability at room temperature while maintaining full catalytic activity. Pd-PDMS efficiently promotes three pharmaceutically relevant reactions: Suzuki coupling (80% yield), copper-free Sonogashira coupling (90% yield at 55 °C), and Heck coupling (80% yield at 90 °C). The copper-free Sonogashira protocol eliminates toxic copper cocatalysts, phosphine ligands, and organic bases while operating under mild conditions. Most significantly, palladium contamination in products reaches ultra-low levels of 22 ppb (Sonogashira, Suzuki) and 167 ppb (Heck), representing a 60–450-fold improvement over European Medicines Agency requirements (10 ppm). The catalyst exhibits excellent recyclability without activity loss over multiple cycles, with simple washing protocols between uses. Scanning electron microscopy and X-ray photoelectron spectroscopy confirmed uniform Pd-PDMS coating on carbon fibers, while density functional theory calculations revealed specific coordination interactions between the palladium complex and carbon support at 3.26 Å distance. This convergence of pharmaceutical-grade metal contamination control, exceptional stability, and multi-reaction versatility establishes a significant advancement for sustainable cross-coupling catalysis in pharmaceutical applications. Full article

Herein, we report a one-pot palladium- and ligand-free tandem Sonogashira coupling/regioselective 6-endo-dig oxacyclization reaction of 2,4-diiodo-1-methyl-imidazole-5-carboxylic acid with terminal alkynes mediated by Copper(I). This impressive approach offers a straightforward, practical, and efficient tandem procedure for accessing 2-alkynylated pyrano[4,3-d]imidazol-4-one in moderate to good yields with an exclusive 6-endo-dig oxacyclization. Notably, this cost-effective methodology demonstrates broad substrate compatibility with various commercially available aliphatic and (hetero)aromatic terminal alkynes. Furthermore, DFT studies were performed to elucidate the origin of this regioselective 6-endo-dig oxacyclization reaction. Full article

Coordination-driven Cu(I) complexes constitute an interesting class of materials with rich opto-electronic properties and diverse applications. Various homo- and heteroleptic Cu(I) complexes have been reported in the literature. In continuation with our quest for new materials, we report herein two novel coordination-driven self-assembled Cu(I) complexes: the homoleptic (1) and the heteroleptic (2) complexes based on the 6,6′-bis(phenylethynyl)-2,2′-bipyridine (L1) and 2,9-dimethyl-1,10-phenanthroline (dmph) ligands. L1 was prepared by a Pd(II)-catalyzed Sonogashira cross-coupling reaction between phenylactylene and 6,6′-dibromo-2,2′-bipyridine. Homo- and heteroleptic Cu(I) complexes were obtained by the self-assembly of L1 and dmph ligands. Complexes (1) and (2) were obtained in high yields, and are soluble in common organic solvents and stable at room temperature over a long period of time. The optical (absorption and emission) properties of both complexes were evaluated. The optical properties in solution are a function of the ligands and varied for the complexes. Complex (2) was also characterized by single-crystal X-ray diffraction and the intermolecular interaction was studied using Hirschfeld surface analysis. In the solid state, complex (2) exhibited four-coordinate distorted tetrahedral geometry around Cu(I). Density functional theory (B3LYP/6-311++G(d,p) was utilised to determine various molecular descriptors. Full article

Thin films of poly(arylene ethynylene)-conjugated polymers, including low-energy-gap donor–acceptor polymers, can be prepared via stepwise polymerization utilizing surface-confined Sonogashira cross-coupling. This robust and efficient polymerization protocol yields conjugated polymers with a precise molecular structure and with nanometer-level control of the organization and the uniform alignment of the macromolecular chains in the densely packed film. In addition to high stability and predictable and well-defined molecular organization and morphology, the surface-confined conjugated polymer chains experience significant interchain electronic interactions, resulting in dominating intermolecular π-electron delocalization which is primarily responsible for the electronic and spectroscopic properties of polymer films. The fluorescent films demonstrate remarkable performance in chemosensing applications, showing a turn-off fluorescent response on the sub-ppt (part per trillion) level of nitroaromatic explosives in water. This unique sensitivity is likely related to the enhanced exciton mobility in the uniformly aligned and structurally monodisperse polymer films. Full article

A general approach is presented for synthesizing alkyne-modified nucleoside triphosphates via the Sonogashira cross-coupling reaction of unprotected halogenated 2ʹ-deoxynucleoside, followed by monophosphorylation and the reaction of the corresponding phosphoromorpholidate with tributylammonium pyrophosphate. A highly efficient approach for the milligram-scale synthesis of base-modified nucleoside triphosphates with an amino acid-like side chain was developed. The present chemical method outweighs the other reported methods of a base-modified nucleoside triphosphates synthesis in terms of it being a protection-free strategy, the shortening of reaction steps, and increased yields (about 70%). The resulting 8-alkynylated dATP was tested as a substrate for DNA polymerases in a primer extension reaction. Full article

Pterins are molecules of substantial interest as they occur in nature in a number of forms with quite distinct and often indispensable roles. Chemically, the synthesis of the principle pterin scaffold is comparably simple, while the insolubility of the pterin building block renders synthetic derivatization extremely difficult. When aiming at modeling naturally occurring pterins of extended chemical structure, this is a considerable problem. A notable set of strategies was developed in the course of the present study, which are able to overcome the lack of reactivity of the pterin backbone. These include a strategic choice regarding protection groups, uncommon chemical transformation, ball milling and combinations thereof. Some novel pterins with quite distinct substitution motifs were successfully synthesized and characterized by spectroscopic and spectrometric analyses as well as single-crystal structural analyses for three of them. Full article

Background/Objectives. The rise of antibiotic-resistant pathogens represents a significant global challenge in infectious disease control, which is amplified by the decline in the discovery of novel antibiotics. Staphylococcus aureus continues to be a highly significant pathogen, causing infections in multiple organs and tissues in both healthcare institutions and community settings. The bacterium has become increasingly resistant to all available antibiotics. Consequently, there is an urgent need for novel small molecules that inhibit the growth or impair the survival of bacterial pathogens. Given their large structural and chemical diversity, as well as often unique mechanisms of action, natural products represent an excellent avenue for the discovery and development of novel antimicrobial treatments. Anaephene A and B are two such naturally occurring compounds with significant antimicrobial activity against Gram-positive bacteria. Here, we report the rapid syntheses and biological characterization of five novel anaephene derivatives, which display low cytotoxicity against mammalian cells but potent antibacterial activity against various S. aureus strains, including methicillin-resistant S. aureus (MRSA) and the multi-drug-resistant community-acquired strain USA300LAC. Methods. A Sonogashira cross-coupling reaction served as the key step for the synthesis of the alkyl pyridinol products. Results/Conclusions. Using the compound JC-01-074, which displays bactericidal activity already at low concentrations (MIC: 16 μg/mL), we provide evidence that alkyl pyridinols target actively growing and biofilm-forming cells and show that these compounds cause disruption and deformation of the staphylococcal membrane, indicating a membrane-associated mechanism of action. Full article

The microwave-assisted Sonogashira C-C cross-coupling reaction catalysed by Pd ionanofluids based on bis(trifluoromethane-sulfonyl)imide (NTf₂) ionic liquids, [C_nmim][NTf₂] (n = 4, 6 or 8), is described here. An organic solvent- and Cu(I)-free methodology running under very mild conditions was established by creating in situ catalysts from Pd(II) salts and [C_nmim][NTf₂]. The microwave-irradiated catalytic systems quickly yielded almost quantitative conversions of 4-bromoanisole and phenylacetylene (model reaction) into the desired 1-methoxy-4-(phenylethynyl)benzene as a single product, and a good recyclability of the Pd ionanofluids. Full article

As a development of our research on biocompatible glycoconjugate probes and specifically multi-chromophoric systems, herein, we report the synthesis and early bactericidal tests of two luminescent glycoconjugates whose basic structure is characterized by two boron dipyrromethene difluoride (BODIPY) moieties and three galactoside rings mounted on an oligophenylene ethynylene (OPE) skeleton. BODIPY fluorophores have found widespread application in many branches of biology in the last few decades. In particular, molecular platforms showing two different BODIPY groups have unique photophysical behavior useful in fluorescence imaging. Construction of the complex architecture of the new probes is accomplished through a convergent route that exploits a series of copper-free Heck–Cassar–Sonogashira cross-couplings. The great emergency due to the proliferation of bacterial infections, in conjunction with growing antibiotic resistance, requires the production of new multifunctional drugs and efficient methods for their targeted delivery to control bacteria-associated diseases. Preliminary studies of the glycoconjugate properties as antibacterial agents against representatives of Gram-negative (P. aeruginosa) and Gram-positive (S. aureus) pathogens, which are associated with chronic infections, indicated significant bactericidal activity ascribable to their structural features. Full article

Stable palladium (II) complexes, incorporating a double (N-benzoylthiourea) arrangement bonded to a complex heterocyclic scaffold, are used as precursors of catalytic species able to promote Suzuki–Miyaura, Mizoroki–Heck, Hiyama, Buchwald–Hartwig, Hirao and Sonogashira–Hagihara cross-coupling transformations in water. These sustainable processes are chemoselective and very versatile. The nanoparticles responsible for these catalytic reactions were analyzed and studied. Their usefulness is demonstrated after several tests and analyses. The heterogeneous character of this species in water was also confirmed. Full article

The increase of noble-metal-free catalysis in organic chemistry is a trending topic in constant growth due to the price increase of noble metals and their scarce abundance. As a result, many earth-abundant transition-metal complexes containing nickel, iron, or cobalt have been successfully applied in the homogeneous catalysis of a wide number of cross-coupling reactions, and the use of pincer complexes based on these earth-abundant metals was recently explored, affording interesting results. Thus, this review provides a general overview of earth-abundant 3D pincer complexes and their application during the last decade as catalysts in cross-coupling reactions such as Kumada–Corriu, Suzuki–Miyaura, Sonogashira, C–S cross-coupling, and C–N bond-forming reactions. Full article

Organotitanium compounds find application in diverse reactions, including carbon–carbon bond formation and oxidation. While titanium (IV) compounds have been used in various applications, the potential of bis(cyclopentadienyl)diaryltitanium in cross-coupling reactions remains unexplored. This study focuses on Sonogashira-type cross-coupling reactions involving terminal alkynes and organotitanium compounds. Diaryltitanocenes were synthesized using titanocene dichloride with lithium intermediates derived from aryl iodide. Under open-flask conditions, reactions of diphenyltitanocenes with ethynylbenzene in the presence of 20 mol% Pd(OAc)₂ in DMF produced coupling products in a remarkable 99% yield. Various diaryltitanocenes and alkynes under standard conditions yielded corresponding cross-coupling products with moderate to good yields. Notably, the Sonogashira-type alkynylation proceeds under mild conditions, including open-flask conditions, and without the need for a base. Furthermore, this cross-coupling is atom-economical and involves the active participation of both aryl groups of the diaryltitanocene. Remarkably, this study presents the first example of a Sonogashira-type cross-coupling using titanium compounds as pseudo-halides. Full article

Nowadays, amino acids (AAs) and peptides with bulky side chains hold significant interest for organic synthesis and the modern pharma industry. Non-proteinogenic (or unnatural) AAs are key building blocks used for obtaining pharmaceutically relevant peptides and for the development of chiral molecular catalysts, and they are extensively used in the total synthesis of complex natural compounds. Thus, an elaboration of cost-effective methods for the preparation of novel unnatural AAs to increase their structural diversity is highly desirable. In this context, herein, we present an asymmetric metal-templated synthesis of a number of enantiomerically pure (S)-2-amino-2-methyl-5-arylpent-4-ynoic acids starting from commercially available reagents and Belokon’s chiral auxiliary (S)-BPB, namely (S)-2-(N-benzylprolyl)aminobenzophenone. The construction of a chiral Ni(II) complex from alanine (Ala) and the subsequent propargylation, arylation by the Sonogashira cross-coupling reaction using various aryl halides, and, finally, an acidic decomposition of the obtained complexes deliver to the target complex α,α-disubstituted AAs featuring a triple bond in a side chain. Next, the Fmoc-protected α-AAs and dipeptide were synthesized. Finally, we examined the obtained α-AAs and peptide as collagenase inhibitors. Full article