Structural Requirements of 1-(2-Pyridinyl)-5-pyrazolones for Disproportionation of Boronic Acids

We observed an unusual formation of four-coordinate boron(III) complexes from the reaction of 1-(2-pyridinyl)-5-pyrazolone derivatives with arylboronic acids in the basic media. The exact mechanism is not clear; however, the use of unprotected boronic acid and the presence of a bidentate ligand appeared to be the key structural requirements for the transformation. The results suggest that base-promoted disproportionation of arylboronic acid with the assistance of the [N,O]-bidentate ligation of 1-(2-pyridinyl)-5-pyrazolone should take place and facilitate the formation of pyrazole diarylborinate. Experiments to obtain a deeper understanding of its mechanism are currently underway.

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

The transition metal (palladium)-catalysed asymmetric 1,4-addition of arylboronic acids to conjugated enones belong to the most important and emerging strategies for the construction of C–C bonds in an asymmetric fashion. This review covers known catalytic systems used for this transformation. For clarity, we are using the type of ligand as a sorting criterion. Finally, we attempted to create a flowchart facilitating the selection of a suitable ligand for a given combination of enone and arylboronic acid.

Systematic Incorporation of Gold Nanoparticles onto Mesoporous Titanium Oxide Particles for Green Catalysts

This report describes the systematic incorporation of gold nanoparticles (AuNPs) onto mesoporous TiO2 (MPT) particles without strong attractive forces to efficiently serve as reactive and recyclable catalysts in the homocoupling of arylboronic acid in green reaction conditions. Unlike using nonporous TiO2 particles and conventional SiO2 particles as supporting materials, the employment of MPT particles significantly improves the loading efficiency of AuNPs. The incorporated AuNPs are less than 10 nm in diameter, regardless of the amount of applied gold ions, and their surfaces, free from any modifiers, act as highly reactive catalytic sites to notably improve the yields in the homocoupling reaction. The overall physical properties of the AuNPs integrated onto the MPT particles are thoroughly examined as functions of the gold content, and their catalytic functions, including the rate of reaction, activation energy, and recyclability, are also evaluated. While the rate of reaction slightly increases with the improved loading efficiency of AuNPs, the apparent activation energies do not clearly show any correlation with the size or distribution of the AuNPs under our reaction conditions. Understanding the formation of these types of composite particles and their catalytic functions could lead to the development of highly practical, quasi-homogeneous catalysts in environmentally friendly reaction conditions.

Palladium Catalyzed α,β-Homodiarylation of Vinyl Esters in Aqueous Medium

A palladium catalyzed 1,2-diarylation of vinyl esters with sustainable arylbornic acids in water has been developed. This newly elaborated protocol features good functional group tolerance and provides a one-step access to 1,2-diaryletahol derivatives under mild reaction conditions. The presented reaction can be carried out in water smoothly without the addition of any ligands at ambient temperature what makes this procedure environmentally benign. The transformation occurs within a single catalytic cycle and is feasible due to the modification of transition metal catalytic activity through the influence of π-acceptor olefin (benzoquinone) as well as the polar protic reaction medium (water in particular). Moreover, the protocol allows to generate entire compounds libraries (highly profitable in medicinal chemistry) and utilizes sustainable arylboronic acid as coupling partners under mild conditions.

Precision synthesis of fluorene-thiophene alternating copolymer by means of Suzuki-Miyaura catalyst-transfer condensation polymerization: importance of the position of alkyl substituent on thiophene of biaryl monomer to suppress disproportionation

Suzuki-Miyaura catalyst-transfer condensation polymerization (CTCP) of fluorene-thiophene biaryl monomers was investigated for the synthesis of well-defined poly(fluorene-alt-thiophene). Model reactions of α,ω-dibromo(fluorene-thiophene) with arylboronic acid esters showed that t-Bu3P Pd and...