l-Proline catalyzed selective synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles

Sustainable and Advanced LED-Implanted Microfluidic Photoreactor with Coupled Optical Fiber Enabling Efficient Photocatalytic Synthesis Beside Online Reaction Progress Monitoring

The conventional methods for the photoinduced synthesis of benzimidazoles may need further improvement regarding a safer and energy-efficient synthesis platform with in-process monitoring for maximum yield within a much reduced reaction time. This work describes the use of a novel optofluidic Lab-on-a-Chip technology for safer, energy-efficient, and expedited synthesis of benzimidazole derivatives in excellent yields along with real-time quantitative measurement during product formation. This innovative method involves synthesis within LED-embedded microfluidic reactors, allowing for rapid synthesis of benzimidazole derivatives via photoinduced condensation cyclization reactions of aryl aldehydes and o-phenylenediamines using a Rose Bengal/fluorescein photocatalyst. It results in good to excellent yields (85-94%) in a notably shorter period of time (10 min) as compared to that for the batch protocol reaction (2-3 h). The incorporation of a reaction-monitoring microfluidic device precisely connected to the microfluidic reactor (microreactor) unit successfully avoids interference from light sources, ensuring consistent UV-vis spectroscopic observations of the produced benzimidazole derivatives. This LED-embedded microfluidic device's capability of photoinduced synthesis, along with real-time spectroscopic analysis, represents a promising breakthrough in organic synthesis. The proposed approach minimizes the potential for accidents, prevents waste of chemicals, maximizes atom economy, and designs an energy-efficient synthesis route, along with real-time in-process monitoring.

Agro-waste sourced catalyst as an eco-friendly and sustainable approach for Knoevenagel condensation reaction

Background:

The present work describes an eco-friendly and sustainable approach for the Knoevenagel condensation of an aromatic aldehyde with ethyl cyanoacetate, and salicylaldehyde with Meldrum acid for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin (2-oxo-2H-1-benzopyran) derivatives, respectively. The reaction performed under greener catalytic media Water Extract of Watermelon Fruit Peel Ash (WEWFPA) is an eco-friendly protocol derived from the agro-waste feedstock. Various protocols have been reported for the synthesis of Knoevenagel condensation reaction using a hazardous catalyst or/and solvent found toxic to the environment, reaction time longer, poor yield, and required purification of the final product. The present method provides several added advantages of being completely greener, economic, giving high yield, inexpensive catalyst, and the final product isolated in pure form with good yield.

Objective:

The objective of the study was to develop a green methodology for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives.

Results:

The agro-waste based catalyst developed avoids the use of external inorganic/organic base, additives, and solvent-free synthesis of Knoevenagel condensation of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives under rt and microwave irradiation, respectively described. The microwave irradiation condition requires less time for the completion of the reaction and also gave better yield isolation

Methods:

We have demonstrated WEWFPA as a greener homogenous agro-waste is employed under rt stirring and microwave irradiation for the economic synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives. The developed method was found robust, non-hazardous and solvent-free with simple work-up gave target product.

Conclusion:

In conclusion, we have established an efficient, simple, agro-waste based catalytic approach for the synthesis of ethylbenzylidenecyanoacetate and 3-carboxy coumarin derivatives employing WEWFPA as an efficient catalyst under rt stirring and microwave synthesis, respectively. The method is a greener, economical and eco-friendly approach for the synthesis of Knoevenagel condensation products. The advantages of the present approach are solvent-free, no external metal, chemical base free, short reaction time and isolated product in good to excellent yields. The catalyst is agro-waste derived, which has abundant in natural sources, thus making the present approach a greener one.

Ultrasound-Promoted Sustainable Synthesis and Antimicrobial Evaluation of 2-Aryl Benzimidazoles Catalyzed by BPAE at Room Temperature

Background:

Present-day chemists are more interested in developing and using green chemistry protocol for various organic transformations, which employ natural feedstock extracts, and solvent-free, and greener catalysts; they are well known for their non-hazardous nature and have replaced many organic and inorganic based catalysts. In literature, the reported homogenous catalytic approaches have been employed for various bioactive heterocycle syntheses, which follow the green chemistry principle established for various organic transformations catalyzed by WERSA, BFE, WEPPA, WEMFSA, WEMPA, and Eichhorniacrassipes. Among them, 2-aryl benzimidazole derivatives have emerged as prominent molecules with a wide variety of applications in biological and material science.

Methods:

The agro-waste sourced from the banana peel is utilized for the preparation of BPAE catalyst, which is employed for the synthesis of 2-aryl benzimidazole derivatives under ultrasound waves at room temperature.

Results:

Here, 2-Aryl benzimidazoles synthesized through the reaction of a substituted o-phenylene diamine with substituted benzoyl chloride catalyzed by BPAE under ultrasound waves at room temperature are described. Furthermore, catalyst BPAE is characterized by flame emission spectrometry, SEM-EDX, and XRD techniques.

Conclusion:

The present work established an eco-friendly, sustainable and novel approach for the synthesis of 2-aryl benzimidazoles using natural feedstock BPAE. The major merits of BPAE include its use as an agro-waste-derived catalyst. It is also highly abundant, inexpensive, yields faster reactions, has a simple workup, and does not require the use of column chromatography.

Silica–sulfuric acid and alumina–sulfuric acid: versatile supported Brønsted acid catalysts

–SO3H functionalized silica and alumina have emerged as efficient and eco-compatible heterogeneous solid acid catalysts for the construction of various important molecular skeletons.

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

Heterocycles have been found to be of much importance as several nitrogen- and oxygen-containing heterocycle compounds exist amongst the various USFDA-approved drugs. Because of the advancement of nanotechnology, nanocatalysis has found abundant applications in the synthesis of heterocyclic compounds. Numerous nanoparticles (NPs) have been utilized for several organic transformations, which led us to make dedicated efforts for the complete coverage of applications of metal nanoparticles (MNPs) in the synthesis of heterocyclic scaffolds reported from 2010 to 2019. Our emphasize during the coverage of catalyzed reactions of the various MNPs such as Ag, Au, Co, Cu, Fe, Ni, Pd, Pt, Rh, Ru, Si, Ti, and Zn has not only been on nanoparticles catalyzed synthetic transformations for the synthesis of heterocyclic scaffolds, but also provide an inherent framework for the reader to select a suitable catalytic system of interest for the synthesis of desired heterocyclic scaffold.

p-Toluenesulfonic Acid Coated Natural Phosphate as an Efficient Catalyst for the Synthesis of 2-Substituted Benzimidazole

2-Substituted benzimidazoles are selectively synthesised in high yields via the condensation of o-phenylenediamine derivatives with aldehyde derivatives using catalytic amount of p-toluenesulfonic acid coated natural phosphate (NP/PTSA) under mild conditions. The use of NP/PTSA as a reusable catalyst makes this process simple, convenient, and environmentally friendly.

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.

Structural characterization of two tetra-chlorido-zincate salts of 4-carb-oxy-1H-imidazol-3-ium: a salt hydrate and a co-crystal salt hydrate

Imidazole-containing compounds exhibit a myriad of pharmacological activities. Two tetra-chlorido-zincate salts of 4-carb-oxy-1H-imidazol-3-ium, ImHCO2H+, are reported. Bis(4-carb-oxy-1H-imidazol-3-ium) tetra-chlorido-zincate monohydrate, (C4H5N2O2)2[ZnCl4]·H2O, (I), crystallizes as a monohydrate salt, while bis-(4-carb-oxy-1H-imidazol-3-ium) tetra-chlorido-zincate bis-(1H-imidazol-3-ium-4-carboxyl-ato) monohydrate, (C4H5N2O2)2[ZnCl4]·2C4H4N2O2·H2O, (II), is a co-crystal salt with six residues: two ImHCO2H+ cations, two formula units of the zwitterionic 1H-imidazol-3-ium-4-carboxyl-ate, ImHCO2, one tetra-chlorido-zincate anion and one water mol-ecule disordered over two sites in a 0.60 (4):0.40 (4) ratio. The geometric parameters of the ImHCO2H+ and the ImHCO2 moieties are the same within the standard uncertainties of the measurements. Both compounds exhibit extensive hydrogen bonding, including involvement of the tetra-chlorido-zincate anion, resulting in inter-connected chains of anions joined by water mol-ecules.

Synthesis and characterization of green-emitting Ir(iii) complexes based on a functionalized benzimidazole ligand

Two new Ir(iii) complexes containing a functionalized benzimidazole ligand (L) were successfully synthesized for use in green phosphorescent organic light-emitting diodes.

Isocyanurate-based periodic mesoporous organosilica (PMO-ICS): a highly efficient and recoverable nanocatalyst for the one-pot synthesis of substituted imidazoles and benzimidazoles

Isocyanurate bridging periodic mesoporous organosilica (PMO-ICS) was shown to be a highly active and efficient recyclable nanocatalyst for three-component synthesis of trisubstituted imidazole as well as benzimidazole derivatives in EtOH.

Grindstone chemistry: protic ionic liquid-substrate tuned green synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity

An environmentally benign and highly substrate-protic ionic liquid controlled synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity is demonstrated through grinding a mixture of OPD, aldehydes and catalyst.

Structure determination of three furan-substituted benzimidazoles and calculation of π-π and C-H···π interaction energies

The synthesis and structural characterization of 2-(furan-2-yl)-1-(furan-2-ylmethyl)-1H-benzimidazole [C16H12N2O2, (I)], 2-(furan-2-yl)-1-(furan-2-ylmethyl)-1H-benzimidazol-3-ium chloride monohydrate [C16H13N2O2(+)·Cl(-)·H2O, (II)] and the hydrobromide salt 5,6-dimethyl-2-(furan-2-yl)-1-(furan-2-ylmethyl)-1H-benzimidazol-3-ium bromide [C18H17N2O2(+)·Br(-), (III)] are described. Benzimidazole (I) displays two sets of aromatic interactions, each of which involves pairs of molecules in a head-to-tail arrangement. The first, denoted set (Ia), exhibits both intermolecular C-H···π interactions between the 2-(furan-2-yl) (abbreviated as Fn) and 1-(furan-2-ylmethyl) (abbreviated as MeFn) substituents, and π-π interactions involving the Fn substituents between inversion-center-related molecules. The second, denoted set (Ib), involves π-π interactions involving both the benzene ring (Bz) and the imidazole ring (Im) of benzimidazole. Hydrated salt (II) exhibits N-H···OH2···Cl hydrogen bonding that results in chains of molecules parallel to the a axis. There is also a head-to-head aromatic stacking of the protonated benzimidazole cations in which the Bz and Im rings of one molecule interact with the Im and Fn rings of adjacent molecules in the chain. Salt (III) displays N-H···Br hydrogen bonding and π-π interactions involving inversion-center-related benzimidazole rings in a head-to-tail arrangement. In all of the π-π interactions observed, the interacting moieties are shifted with respect to each other along the major molecular axis. Basis set superposition energy-corrected (counterpoise method) interaction energies were calculated for each interaction [DFT, M06-2X/6-31+G(d)] employing atomic coordinates obtained in the crystallographic analyses for heavy atoms and optimized H-atom coordinates. The calculated interaction energies are -43.0, -39.8, -48.5, and -55.0 kJ mol(-1) for (Ia), (Ib), (II), and (III), respectively. For (Ia), the analysis was used to partition the interaction energies into the C-H···π and π-π components, which are 9.4 and 24.1 kJ mol(-1), respectively. Energy-minimized structures were used to determine the optimal interplanar spacing, the slip distance along the major molecular axis, and the slip distance along the minor molecular axis for 2-(furan-2-yl)-1H-benzimidazole.

Benzimidazole-1,2,3-triazole hybrid molecules: synthesis and evaluation for antibacterial/antifungal activity

A novel series of hybrid molecules 4a-i and 5a-i were prepared by condensation of 4-(trimethylsilylethynyl)benzaldehyde 1 with substituted o-phenylenediamines. These in turn were reacted with 2-(azidomethoxy)ethyl acetate in a Cu alkyne-azide cycloaddition (CuAAC) to generate the 1,2,3-triazole pharmacophore under microwave assistance. The newly synthesized compounds were examined for their in vitro antimicrobial activities against Gram-positive and Gram-negative bacteria and the phytopathogenic fungi Verticillium dahliae and Fusarium oxysporum f. sp. albedinis. 2-((4-(4-(5-Trifluoromethyl benzimidazol-2-yl)phenyl)-1,2,3-triazol-1-yl)methoxy)ethanol 5e showed a moderate inhibition of 30% in the Foa sporulation test.

Facile and efficient one-pot synthesis of benzimidazoles using lanthanum chloride

BACKGROUND

We report the synthesis of benzimidazoles using lanthanum chloride as an efficient catalyst. One-pot synthesis of 2-substituted benzimidazole derivatives from o-phenylenediamine and a variety of aldehydes were developed under mild reaction conditions.

RESULTS

We have examined the effect of different solvents using the same reaction conditions. The yield of the product varied with the nature of the solvents, and better conversion and easy isolation of products were found with acetonitrile. In a similar manner, the reaction with o-phenylenediamine and 3,4,5-trimethoxybenzaldehyde was carried out without any solvents. The observation shows that the reaction was not brought into completion, even after starting for a period of 9 h, and the reaction mixture showed a number of spots in thin-layer chromatography.

CONCLUSIONS

In conclusion, lanthanum chloride has been employed as a novel and efficient catalyst for the synthesis of benzimidazoles in good yields from o-phenylenediamine and a wide variety of aldehydes. All of the reactions were carried out in the presence of lanthanum chloride (10 mol%) in acetonitrile at room temperature.