Construction of Spiro[benzo[a]acridine-12,4'-imidazolidine]-2',5'-dione Derivatives via Ring-Opening and Recyclization of Isatins and C-OH Cleavage of 2-Naphthol

An efficient three-component reaction to access spiro[benzo[a]acridine-12,4'-imidazolidine]-2',5'-dione derivatives has been developed through the ring-opening and recyclization process of isatins and dehydroxylation of 2-naphthol, which is different from their conventional reaction modes. Experimental observations suggest that p-toluenesulfonic acid is the key factor that promotes the success of this synthetic strategy. The research provided a novel approach for the construction of spiro compounds from isatins and 2-naphthol in organic synthesis.

Catalysis with magnetically retrievable and recyclable nanoparticles layered with Pd(0) for C–C/C–O coupling in water

Nanoparticles layered with palladium(0) were prepared from nano-sized magnetic Fe₃O₄ by coating it with silica and then reacting sequentially with phenylselenyl chloride under an N₂ atmosphere and palladium(ii) chloride in water. The resulting Fe₃O₄@SiO₂@SePh@Pd(0) NPs are magnetically retrievable and the first example of NPs in which the outermost layer of Pd(0) is mainly held by selenium. The weight percentage of Pd in the NPs was found to be 1.96 by ICP-AES. The NPs were authenticated via TEM, SEM-EDX, XPS, and powder XRD and found to be efficient as catalysts for the C–O and C–C (Suzuki–Miyaura) coupling reactions of ArBr/Cl in water. The oxidation state of Pd in the NPs having size distribution from ∼12 to 18 nm was inferred as zero by XPS. They can be recycled more than seven times. The main features of the proposed protocols are their mild reaction conditions, simplicity, and efficiency as the catalyst can be separated easily from the reaction mixture by an external magnet and reused for a new reaction cycle. The optimum loading (in mol% of Pd) was found to be 0.1–1.0 and 0.01–1.0 for O-arylation and Suzuki–Miyaura coupling, respectively. For ArCl, the required amount of NPs was more as compared to that needed for ArBr. The nature of catalysis is largely heterogeneous.

Fe₃O₄@SiO₂@SePh@Pd(0) (Pd, 1.96%) as the first example of NPs having a Pd(0) layer held by selenium can execute C–C/C–O coupling in 2–6 h (80 °C).

Ullmann Reactions of Carbon Nanotubes-Advantageous and Unexplored Functionalization toward Tunable Surface Chemistry

We demonstrate Ullmann-type reactions as novel and advantageous functionalization of carbon nanotubes (CNTs) toward tunable surface chemistry. The functionalization routes comprise O-, N-, and C-arylation of chlorinated CNTs. We confirm the versatility and efficiency of the reaction allowing functionalization degrees up to 3.5 mmol g⁻¹ by applying both various nanotube substrates, i.e., single-wall (SWCNTs) and multi-wall CNTs (MWCNTs) of various chirality, geometry, and morphology as well as diverse Ullmann-type reagents: phenol, aniline, and iodobenzene. The reactivity of nanotubes was correlatable with the nanotube diameter and morphology revealing SWCNTs as the most reactive representatives. We have determined the optimized conditions of this two-step synthetic protocol as: (1) chlorination using iodine trichloride (ICl₃), and (2) Ullmann-type reaction in the presence of: copper(I) iodide (CuI), 1,10-phenanthroline as chelating agent and caesium carbonate (Cs₂CO₃) as base. We have analyzed functionalized CNTs using a variety of techniques, i.e., scanning and transmission electron microscopy, energy dispersive spectroscopy, thermogravimetry, comprehensive Raman spectroscopy, and X-ray photoelectron spectroscopy. The analyses confirmed the purely covalent nature of those modifications at all stages. Eventually, we have proved the elaborated protocol as exceptionally tunable since it enabled us: (a) to synthesize superhydrophilic films from—the intrinsically hydrophobic—vertically aligned MWCNT arrays and (b) to produce printable highly electroconductive pastes of enhanced characteristics—as compared for non-modified and otherwise modified MWCNTs—for textronics.

Ligand-free Cu(ii)-catalyzed aerobic etherification of aryl halides with silanes: an experimental and theoretical approach

Owing to their wide occurrence in nature and immense applications in various fields, the synthesis of aryl alkyl ethers has remained a focus of interest.

Diaryl ethers synthesis: nano-catalysts in carbon-oxygen cross-coupling reactions

The diaryl ether moiety is not only prevalent in a significant number of natural products and synthetic pharmaceuticals but also widely found in many pesticides, polymers, and ligands. Ullmann-type cross-coupling reactions between phenols and aryl halides are regarded as one of the most important methods for the synthesis of this important and versatile structural motif. In recent years, the use of nano-sized metal catalysts in this coupling reaction has attracted a lot of attention because of these catalysts with their high surface-to-volume ratio, high surface energy, and reactive morphology allows for rapid C-O bond formation under mild and ligand-free conditions. In this review we will highlight the power of these catalysts in Ullmann-type C-O cross-coupling reactions.

Copper NPs supported on hematite as magnetically recoverable nanocatalysts for a one-pot synthesis of aminoindolizines and pyrrolo[1,2-a]quinolines

Copper mixed oxide NPs supported on a hematite surface were achieved using a facile hydrothermal method in a single step. The catalytic potential of the Cu@Fe₂O₃ NPs was explored for the synthesis of aminoindolizines and pyrrolo[1,2-a]quinolines.

CsF/clinoptilolite: an efficient solid base in SNAr and copper-catalyzed Ullmann reactions

CsF/clinoptilolite was found to be an efficient solid base catalyst for both SNAr and Ullmann ether reactions. A general and efficient one-step procedure was developed for the synthesis of biaryl ethers via direct coupling of electron-deficient aryl halides to phenols using CsF/clinoptilolite. The protocol was also applied to electron-rich aryl halides by addition of a catalytic amount of copper oxide nanoparticles. Both SNAr and Ullmann reactions were rapid and provided good to excellent yields.

Highly efficient CuxO/TiO2 catalysts: controllable dispersion and isolation of metal active species

Cu_xO/TiO₂ architectures with enhanced dispersion of the active phase are synthesized by a MOF-templated method. Such composites show excellent catalytic activity for CO oxidation.

Synthesis of copper nanoparticles supported on a microporous covalent triazine polymer: an efficient and reusable catalyst for O-arylation reaction

Cu NPs immobilized on a microporous covalent triazine polymer obtained by a cost-effective synthesis method were evaluated as a catalyst for Ullmann coupling of O-arylation.

Graphene-supported Cu2O nanoparticles: an efficient heterogeneous catalyst for C–O cross-coupling of aryl iodides with phenols

Cu₂O/graphene as a heterogeneous catalyst can efficiently catalyze the C–O cross-coupling of aryl iodides with phenols.