Acid-catalyzed solvent-free synthesis of 2-arylbenzimidazoles under microwave irradiation

Cu(II)-SBA-15 mediated synthesis of 2-aryl benzimidazoles and benzoxazoles: a sustainable approach

Benzimidazole and benzoxazole scaffolds are widely recognized for their presence in molecules with diverse pharmacological activities, including antiviral, antiulcer, antihypertensive, and anticancer effects. Motivated by their structural and synthetic significance, this work presents a green and efficient approach for the synthesis of 2-aryl benzimidazoles and benzoxazoles via the condensation of o-phenylenediamine or o-aminophenol with substituted benzaldehydes. The reaction is catalysed by Cu(II)-SBA-15, a recyclable and eco-friendly heterogeneous catalyst, offering an environmentally benign alternative to conventional methods. The catalytic system demonstrated a pristine reaction profile, with 100% conversion and 74-86% yields in a short timeframe. The heterogeneous mesoporous Cu-SBA-15 catalyst exhibited easy separability through simple centrifugation/filtration, emerging as a promising catalyst for the efficient and facile synthesis of 2-aryl benzimidazoles and 2-aryl benzoxazoles. Significantly, the catalyst demonstrated broad substrate scope and good recyclability with sustained efficiency, with its commercial viability impending.

Molecularly Engineering Defective Basal Planes in Molybdenum Sulfide for the Direct Synthesis of Benzimidazoles by Reductive Coupling of Dinitroarenes with Aldehydes

Developing more sustainable catalytic processes for preparing N-heterocyclic compounds in a less costly, compact, and greener manner from cheap and readily available reagents is highly desirable in modern synthetic chemistry. Herein, we report a straightforward synthesis of benzimidazoles by reductive coupling of o-dinitroarenes with aldehydes in the presence of molecular hydrogen. An innovative molecular cluster-based synthetic strategy that employs Mo₃S₄ complexes as precursors have been used to engineer a sulfur-deficient molybdenum disulfide (MoS₂)-type material displaying structural defects on both the naturally occurring edge positions and along the typically inactive basal planes. By applying this catalyst, a broad range of functionalized 2-substituted benzimidazoles, including bioactive compounds, can be selectively synthesized by such a direct hydrogenative coupling protocol even in the presence of hydrogenation-sensitive functional groups, such as double and triple carbon-carbon bonds, nitrile and ester groups, and halogens as well as diverse types of heteroarenes.

A Photochemical Intramolecular C-N Coupling Toward the Synthesis of Benzimidazole-Fused Phenanthridines

Herein, we report a direct photochemical dehydrogenative C-N coupling of unactivated C(sp²)-H and N(sp²)-H bonds. The catalysts or additive-free transformation of 2-([1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole to benzo[4,5]imidazo[1,2-f]phenanthridine was achieved at ∼350 nm of irradiation via ε-hydrogen abstraction. DFT calculations helped to understand that the N-H···π interaction was essential for the reaction to proceed at a lower energy than expected.

Heterogeneous Catalytic Synthesis of 2-Methylbenzimidazole from 2-Nitroaniline and Ethanol Over Mg Modified Cu-Pd/γ-Al2O3

The direct synthesis of benzimidazoles from 2-nitroaniline and ethanol over Cu-Pd/γ-Al2O3 catalysts has the advantages of requiring easily available starting materials, having high efficiency, and a simple procedure. The modification by Mg of the Cu-Pd/γ-Al2O3 catalyst could improve the catalytic activity significantly. The addition of Mg to the Cu-Pd/γ-Al2O3 catalyst could maintain and promote the formation of CuPd alloy active sites. Meanwhile, the basicity of the support was enhanced appropriately by Mg, which generated more basic sites (Al-Oδ−) to accelerate the dehydrogenation of alcohol and increased the rate of the whole coupled reaction. The 2-nitroaniline was completely converted over Cu-Pd/(Mg)γ-Al2O3 after reacting for six hours, and the yield of 2-methylbenzimidazole was 98.8%. The results of this work provide a simple method to develop a more efficient catalyst for the “alcohol-dehydrogenation, hydrogen transfer and hydrogenation” coupled reaction system.

Brønsted acidic reduced graphene oxide as a sustainable carbocatalyst: a selective method for the synthesis of C-2-substituted benzimidazole

A selective and sustainable methodology for the synthesis of C-2-substituted benzimidazole has been demonstrated using benzenesulfonic acid-grafted reduced graphene oxide as a Brønsted acidic carbocatalyst.

CO2 adsorption and catalytic application of imidazole ionic liquid functionalized porous organic polymers

A class of imidazole ionic liquid functionalized porous organic polymers has been synthesized by the Friedel–Crafts alkylation reaction. The resulting materials show high CO₂ uptake and catalytic activity in the syntheses of benzimidazole derivatives.

Synthesis of amino ester-embedded benzimidazoles: a one-pot sequential protocol under metal-free neutral conditions

A one-pot three-component protocol has been developed for the synthesis of amino ester-embedded benzimidazoles under metal-free neutral conditions. Sequentially, the methodology involves coupling of an amino ester with 1-fluoro-2-nitrobenzene, reduction of the coupled nitroarene by sodium dithionite, and cyclization of the corresponding diamine with an aldehyde.

Accessing Benzimidazoles via a Ring Distortion Strategy: An Oxone Mediated Tandem Reaction of 2-Aminobenzylamines

An exceptional oxone mediated tandem transformation of 2-aminobenzylamines to 2-substituted benzimidazoles is reported. It occurs at room temperature with aromatic, heteroaromatic, and aliphatic aldehydes. In this reaction initial condensation of 2-aminobenzylamine with appropriate aldehydes afforded a tetrahydroquinazoline intermediate which underwent oxone-mediated ring distortion to afford the desired compounds in moderate to excellent yields.

Catalytic transfer hydrogenation of azobenzene by low-valent nickel complexes: a route to 1,2-disubstituted benzimidazoles and 2,4,5-trisubstituted imidazolines

The one-pot synthesis of 1,2-disubstituted benzimidazoles by the transfer hydrogenation of azobenzene, using benzylamine as a hydrogen donor is reported, catalyzed by 2 mol% of [Ni(COD)₂] : dippe.

Acetic acid-promoted condensation of o-phenylenediamine with aldehydes into 2-aryl-1-(arylmethyl)-1H-benzimidazoles under microwave irradiation

An efficient and simple procedure was developed for the green synthesis of various 2-aryl-1-(arylmethyl)-1H-benzimidazoles in high yields by acetic acid-promoted condensation of o-phenylenediamine with aldehydes in air under microwave irradiation and transition metal catalystfree conditions.