Transition-Metal-Free Transfer Hydrogenative Cascade Reaction of Nitroarenes with Amines/Alcohols: Redox-Economical Access to Benzimidazoles

Generation of C(sp3)-CAr bonds in the synthesis of triarylmethanes (TRAMs): comprehensive progress since 2009

Triarylmethanes are useful compounds in materials science and medicinal chemistry. These moieties are important constituents of dyes and pharmaceuticals. These scaffolds are synthesized either by Friedel-Crafts alkylation of aldehydes and arenes or by the functionalization of diarylmethanes. The development of effective catalytic systems and the discovery of highly regio- and stereoselective methods using Brønsted or Lewis acid catalysts represent particularly important achievements in this field. This review explores the detailed documentation of the various catalytic strategies witnessed since 2009 for the synthesis of triarylmethanes, which could arouse the interest of readers in organic synthesis.

TiO2 nanoparticles decorated with Co-Schiff base-g-C3N4 as an efficient photocatalyst for one-pot visible light-assisted synthesis of benzimidazoles

In this study, a novel heterogeneous visible light-driven nanocatalyst was produced via the complexation of Co(ii) with g-C₃N₄-imine-functionalized TiO₂ nanoparticles. It was characterized using different techniques such as Fourier-transform infrared (FT-IR), energy-dispersive X-ray spectrum (EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), thermogravimetric analysis (TGA), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The catalyst promoted several different transformations in a one-pot reaction sequence: aerobic photooxidation of benzylic alcohols to aldehydes and then the tandem synthesis of benzimidazoles through the dehydrogenative coupling of primary benzylic alcohols and aromatic diamines. The photocatalyst proved to be highly active, robust, selective, and recyclable under organic reaction conditions and provided affordable products with good to high yields. The results proposed that the improved photoactivity predominantly benefits from the synergistic effects of the heterojunction of Co-carbon nitride on TiO₂ nanoparticles. Moreover, this protocol provides standard conditions avoiding undesirable additives and limitations of oxidation methods, and may help to develop a new strategy for the development of photocatalysis based organic transformations.

The Co-g-C₃N₄-imine/TiO₂ nanohybrid promotes different transformations in a one-pot reaction sequence: aerobic photooxidation of benzylic alcohols to aldehydes, and then the tandem synthesis of benzimidazoles.