Eco-friendly synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles using alumina-sulfuric acid as a heterogeneous reusable catalyst

Recent achievements in the synthesis of benzimidazole derivatives

Benzimidazoles are a class of heterocyclic compounds in which a benzene ring is fused to the 4 and 5 positions of an imidazole ring. Benzimidazole refers to the parent compound, while benzimidazoles are a class of heterocyclic compounds having similar ring structures, but different substituents. Benzimidazole derivatives possess a wide range of bioactivities including antimicrobial, anthelmintic, antiviral, anticancer, and antihypertensive activities. Many compounds possessing a benzimidazole skeleton have been employed as drugs in the market. The application of benzimidazoles in other fields has also been documented. The synthesis of benzimidazole derivatives has attracted much attention from chemists and numerous articles on the synthesis of this class of heterocyclic compound have been reported over the years. The condensation between 1,2-benzenediamine and aldehydes has received intensive interest, while many novel methods have been developed. In this article, we will give a comprehensive review of studies on the synthesis of benzimidazole, which date back to 2013. We have also tried to describe reaction mechanisms as much as we can. The work might be useful for chemists who work in the synthesis of heterocycles or drug chemistry.

An elegant approach for selective synthesis of 2-substituted benzimidazoles at room temperature using Ag nanoparticles as an activator: effect of solvent on the selectivity

An expedient, competent, and green protocol was developed for the selective synthesis of 2-substituted benzimidazole by the condensation of 1,2-diaminobenzene and various aldehydes, including aromatic, heteroaromatic, and aliphatic aldehydes, in methanol and water (1:1) as reaction media in the presence of Ag nanoparticles in a one pot operation at room temperature. The selectivity of the protocol for obtaining 2-substituted benzimidazole is highly dependent on the ratios of methanol and water used, as well as the reaction temperature. The present protocol exhibits several advantages, such as high yield, short reaction time, high selectivity, and no side reaction, and it works at room temperature, which makes this methodology green, providing a practical input to the existing procedures available for the synthesis of 2-substituted benzimidazole derivatives.

Recent Developments Towards Synthesis of (Het)arylbenzimidazoles

Benzimidazole is an important heterocycle that is widely researched and utilized by the pharmaceutical industry and is one of the five most commonly used five-membered aromatic heterocyclic compounds approved by the US Food and Drug Administration. In view of their wide-ranging bioactivities, systems containing benzimidazole as one of the moieties occupy a special place among other benzimidazole derivatives. Since 2010, many improved synthetic strategies have been developed for the construction of hetaryl- and arylbenzimidazole molecular scaffolds under environmentally benign conditions. This review emphasizes the recent trends and modifications frequently used in the synthesis of derivatives of benzimidazole such as the Phillips–Ladenburg and Weidenhagen reactions, as well as entirely new methods of synthesis, involving oxidative cyclization, cross-coupling, ring distortion strategy, and rearrangements carried out under environmentally benign conditions.

1 Introduction

2 From 1,2-Diaminobenzenes with Various One-Carbon Unit Suppliers

2.1 Phillips–Ladenburg Reaction

2.1.1 With (Het)arenecarboxylic Acids

2.2.2 With (Het)arenecarboxylic Acid Derivatives

2.2 Weidenhagen Reaction

2.2.1 With (Het)arenecarbaldehydes or (Het)aryl Methyl Ketones

2.2.2 With Primary Alcohols

2.2.3 With Primary Alkylamines

2.2.4 With 2-Methylazaarenes

2.2.5 With Other One-Carbon Fragment Suppliers

3 From 2-Haloacetanilides and Amines

4 From Amidines

5 From Tetrahydroquinazolines

6 Mamedov Rearrangement

7 Conclusions and Outlook

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.

Synthesis and molecular docking studies of imines as α-glucosidase and α-amylase inhibitors

Imine functionality is found in many compounds with important biological activity. Thus, the development of novel synthetic approaches for imines is important. In this work, it is propose an easy, eco-friendly and straightforward synthesis pathway of aryl imines under microwave irradiation catalyzed by Alumina-sulfuric acid. In addition, the in vitro enzymatic inhibition, antioxidant activity and molecular docking studies were performed. The aryl imines were isolated with yields in the range of 37-94%. All aryl imines synthesized were evaluated for in vitro inhibitory potential against α-glucosidase and α-amylase enzymes and the results exhibited that the most of the compounds displayed inhibitory activity against both enzymes. The (E)-1-(4-nitrophenyl)-N-(pyridin-2-yl)methanimine (3d) was 1.15-fold more active than acarbose against α-amylase whilst the (E)-1-phenyl-N-(pyridin-2-yl)methanimine (3c) displayed similar activity that acarbose against α-glucosidase. The molecular docking studies in α-glucosidase and α-amylase reveal that aryl imines mainly establish an H-bond with the R²-subtituent and hydrophobic interactions with the R¹-subtituent. The docking analysis reveals these synthetic aryl imines 3d-i interact in same active site than acarbose drug in both enzymes.

A unique opportunity for the utilization of glass wastes as a resource for catalytic applications: toward a cleaner environment

n-glass-waste-SO₃H at the service of catalytic application.

A waste to wealth approach through utilization of nano-ceramic tile waste as an accessible and inexpensive solid support to produce a heterogeneous solid acid nanocatalyst: to kill three birds with one stone

Waste minimization through the utilization of cost-effective, available, and nontoxic nano-ceramic tile wastes for the heterogenization of sulfuric acid.

Role of graphene oxide as a heterogeneous acid catalyst and benign oxidant for synthesis of benzimidazoles and benzothiazoles

Graphene oxide plays a dual role as active metal-free acid catalyst and as non-toxic oxidant for benzothiazole and benzimidazole synthesis. Isolated partially reduced graphene oxide was re-oxidized to regenerate the catalyst and restore its activity.

l-proline N-sulfonic acid-functionalized magnetic nanoparticles: a novel and magnetically reusable catalyst for one-pot synthesis of 3,4-dihydropyrimidine-2-(1H)-thiones under solvent-free conditions

Synthesis, characterization and utilization of the l-proline N-sulfonic acid-functionalized magnetic nanoparticles as a novel magnetically reusable acid catalyst for the synthesis of 3,4-dihydropyrimidine-2-[1H]thione derivatives is reported.

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.

Molybdate sulfuric acid (MSA): an efficient reusable catalyst for the synthesis of tetrahydrobenzo[4,5]imidazo[2,1-b]quinazolin-1(2H)-ones under solvent-free conditions and evaluation of their in vitro bioassay

The attractive features of this methodology are green and easy workability with high product yields. All the title compounds have good to excellent anti-oxidant and anticancer activity.