H2 Activation with Co Nanoparticles Encapsulated in N-Doped Carbon Nanotubes for Green Synthesis of Benzimidazoles

Multifunctional Heterogeneous Cobalt Catalyst for the One-Pot Synthesis of Benzimidazoles by Reductive Coupling of Dinitroarenes with Aldehydes in Water

The endeavor of sustainable chemistry has led to significant advancements in green methodologies aimed at minimizing environmental impact while maximizing efficiency. Herein, a straightforward synthesis of benzimidazoles by reductive coupling of o-dinitroarenes with aldehydes is reported for the first time in aqueous media while using a non-noble metal catalyst. This work demonstrates that the combination of nitrogen and phosphorous ligands in the synthesis of supported heteroatom-incorporated Co nanoparticles is crucial for obtaining the desired benzimidazoles. The process achieves >99 % conversion, >99 % chemoselectivity and stability for the reduction of dinitroarenes using water as the solvent and hydrogen as the reductant under mild reaction conditions. The robustness of the catalyst has been investigated using several advanced techniques such as HRTEM, HAADF-STEM, XEDS, EELS, and NAP-XPS. In fact, we have shown that the introduction of N and P dopants prevents metal leaching and the sintering of the cobalt nanoparticles. Finally, to explore the general catalytic performance, a wide range of substituted dinitroarenes and benzaldehydes were evaluated, yielding benzimidazoles with competitive and scalable results, including MBIB (94 % yield), which is a compound of pharmaceutical interest.

Nitroarenes and nitroalkenes as potential amino sources for the synthesis of N-heterocycles

Nitro-compounds are one of the cheapest and most readily available materials in the chemical industry and are commonly utilized as versatile building blocks. Previously, the synthesis of N-heterocycles was largely based on anilines. The utilization of nitroarenes and nitroalkenes for the synthesis of N-heterocyclic compounds can save at least one step, however, as compared to anilines. Thus, considerable attention has been paid to nitroarenes and nitroalkenes as new potential amino sources. Significant progress has been made in the reductive cyclization of nitroarenes or nitroalkenes to access various N-heterocycles in recent years. Herein, we comprehensively summarize the recent progress in the construction of N-heterocycles using nitroarenes and nitroalkenes as potential amino sources. The compatibility of the reaction substrate, its mechanism, applications, advantages, and limitations in this field are also discussed in detail.

Tandem Reduction, Ammonolysis, Condensation, and Deamination Reaction for Synthesis of Benzothiadiazines and 1-(Phenylsulfonyl)-1H-benzimidazoles

A novel route for a SnCl₂-promoted tandem reduction, ammonolysis, condensation, and deamination reaction which uses nitrile and 2-nitro-N-phenylbenzenesulfonamide/N-(2-nitrophenyl)benzenesulfonamide to synthesize derivatives of benzothiadiazine/1-(phenylsulfonyl)-1H-benzimidazole has been developed. The method features convenient operation and good functional group tolerance. In addition, it employs unsensitive and inexpensive SnCl₂/i-PrOH as the reaction reagent and provides a direct approach for the synthesis of pharmaceutically important targets.

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

This report describes an efficient transition-metal-free process toward the transfer hydrogenative cascade reaction between nitroarenes and amines or alcohols. The developed redox-economical approach was realized using a combination of KO^tBu and Et₃SiH as reagents, which allows the synthesis of benzimidazole derivatives via σ-bond metathesis. The reaction conditions hold well over a wide range of substrates embedded with diverse functional groups to deliver the desired products in good to excellent yields. The mechanistic proposal has been depicted on the basis of a series of control experiments, mass spectroscopic evidence which is well supported by density functional theory (DFT) calculations with a feasible energy profile.

Hydrogenative coupling of nitriles with diamines to benzimidazoles using lignin-derived Rh2P catalyst

Nitrile (C≡N bond) activation for direct organic synthesis has been less explored so far due to a high redox potential of nitrile and its low dissociation energy of C−CN bond. Herein, we demonstrate a direct reductive coupling of nitriles and 1,2-phenylenediamines to yield various benzimidazoles in excellent yields (95%–99%) by using rhodium phosphide (Rh₂P) catalyst supported on lignin-derived carbon (LC) using H₂ (or hydrazine hydrate) as a hydrogen source. The high catalytic performance of Rh₂P/LC is attributed to enhanced charge transfer to Rh and strong P−Rh interactions. Our isotope trace experiment confirms the presence of H/D exchange between H₂ and the inert –CD₃ group of CD₃CN via an intramolecular D-shift. Reusability of Rh₂P/LC is further demonstrated by a seven-time recycling without evident loss of activity. This research thus highlights a great potential in organic transformation with nitrile as a synthetic building block.

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Nitrile was developed as synthetic building block for organic synthesis

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Reductive coupling of nitriles to 1,2-phenylenediamines yielded benzimidazoles

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Strong P−Rh interaction and charge transfer to Rh enhanced Rh₂P activity

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H/D exchange between H₂ and –CD₃ in CD₃CN occurred via intramolecular D-shift