Convenient one-pot synthesis of 1,2,4-oxadiazoles and 2,4,6-triarylpyridines using graphene oxide (GO) as a metal-free catalyst: importance of dual catalytic activity

TFA-Mediated Synthesis of 1,2,4-Oxadiazoles from Carbamates and Nitriles

An unprecedented protocol for the synthesis of 1,2,4-oxadiazoles from carbamates has been developed by employing nitriles as both substrates and solvents. This one-pot procedure achieves the formation of C═N bonds via TFA-mediated [3+2] annulation. A series of 1,2,4-oxadiazoles are synthesized in moderate to good yields.

Efficient synthesis of symmetrically substituted pyridines and substituted alkenes through green and heterogeneous catalysis with zinc phosphate

This study presents a new environmentally sustainable catalytic method for the synthesis of symmetrically substituted pyridine derivatives and substituted alkene derivatives using zinc phosphate (Zn3(PO4)2·4H2O) as a non-toxic and green heterogeneous catalyst. The catalytic support was prepared by a co-precipitation method, and it was applied for the first time as a heterogeneous catalyst in organic synthesis. Trisubstituted pyridine derivatives were prepared with excellent yields (82-94%) via a three-component, one-pot synthesis of aromatic aldehydes, substituted acetophenones, and ammonium acetate in the presence of 0.4 mol% of Zn3(PO4)2·4H2O using an ethanol/water (4/1) mixture as the solvent, while substituted alkenes were synthesized with up to 90% yield using the prepared catalyst. The experimental results demonstrate the efficiency of these new catalytic syntheses that present various advantages such as short reaction times, excellent yields, and an environmentally friendly profile.

β-Cyclodextrin: a green supramolecular catalyst assisted eco-friendly one-pot three-component synthesis of biologically active substituted pyrrolidine-2-one

A green, novel and eco-efficient synthetic route towards the synthesis of highly substituted bio-active pyrrolidine-2-one derivatives was demonstrated using β-cyclodextrin, a water-soluble supramolecular solid as a green and eco-benign catalyst at room temperature under water-ethanol solvent medium. The exploration of the green catalyst β-cyclodextrin for the metal-free one-pot three-component synthesis of a wide range of highly functionalized bio-active heterocyclic pyrrolidine-2-one moieties from easily available aldehydes and amines explains the superiority and uniqueness of this protocol.

A Graphene Acid - TiO2 Nanohybrid as Multifunctional Heterogeneous Photocatalyst for the Synthesis of 1,3,4-Oxadiazoles

The immobilization of TiO₂ nanoparticles on graphene acid (GA), a conductive graphene derivative densely functionalized with COOH groups, is presented. The interaction between the carboxyl groups of the surface and the titanium precursor leads to a controlled TiO₂ heterogenization on the nanosheet according to microscopic and spectroscopic characterizations. Electronic communication shared among graphene and semiconductor nanoparticles shifts the hybrid material optical features toward less energetic radiation but maintaining the conductivity. Therefore, GA-TiO₂ is employed as heterogeneous photocatalyst for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles using ketoacids and hydrazides as substrates. The material presented enhanced photoactivity compared to bare TiO₂, being able to yield a large structural variety of oxadiazoles in reaction times as fast as 1 h with full recyclability and stability. The carbocatalytic character of GA is the responsible for the substrates condensation and the GA-TiO₂ light interaction ability is able to photocatalyze the cyclization to the final 1,3,4-oxadiazoles, demonstrating the optimal performance of this multifunctional photocatalytic material.