Imidazolium chloride-catalyzed synthesis of benzimidazoles and 2-substituted benzimidazoles from o-phenylenediamines and DMF derivatives

A facile, general, and economical synthesis of diversely functionalized benzimidazoles and 2-substituted benzimidazoles has been realized via the imidazolium chloride-catalyzed cyclization of o-phenylenediamines with DMF derivatives. This protocol shows a broad substrate scope for aliphatic, aromatic, and heteroaromatic amides. A series of benzimidazoles and 2-substituted benzimidazoles have been obtained in moderate to excellent yields.     

Chiral benzimidazoles and their applications in stereodiscrimination processes

Chiral aspects of benzimidazoles have been over-shadowed for a long time due to the large number of reports on benzimidazoles in the medical field in numerous categories of therapeutic agents. The vigorous research activity in chiral applications of benzimidazole derivatives started after bifunctional benzimidazoles made their appearance especially in the last 2–3 decades. Thus, chiral benzimidazoles form a comparatively young branch of chiral chemistry. The presence of pyridine and pyrrole type of nitrogens along with the fused benzene ring confer on this class of molecules, special properties including useful nucleophilicity, hydrogen bonding ability and a rigid backbone, all of which play decisive roles in proven chiral applications. The present review aims to cover the synthetic routes to access chiral benzimidazoles and their applications in a plethora of chiral fields including enantioselective organocatalysis, metal-based catalysis, asymmetric transformations involving benzimidazole-N-heterocyclic carbenes, kinetic resolution, benzimidazole-based macrocyclic hosts in chiral supramolecular chemistry and other miscellaneous chiral applications.     

The reaction of 2-(ω-chloroalkyl)benzimidazoles with thiourea. Studies on heterocyclic compounds. I

By reaction of the appropriate 2-(ω-chloroalkyl)benzimidazoles with thiourea, 2-(α-mercaptoalkyl)benzimidazoles (IV) have been prepared. The attempted preparation of 2-(β- and γ-mercaptoalkyl)benzimidazoles failed. β-Elimination was observed by alkaline treatment of S-[2-(2-benzimidazolyl)-propyl]isothiuronium chloride (VII), whereas 2-(γ-chlorobutyl)benzimidazoles did not give an isothiuronium chloride.     

Rapid and Cheap Synthesis of Benzimidazoles via Intermittent Microwave Promotion: A Simple and Potential Industrial Application of Air as Oxidant

Using inexpensive KI as the catalyst in the presence of ambient air, benzimidazoles were synthesized from aromatic aldehydes and o-phenylenediamine with excellent yields via intermittent microwave irradiation without reflux equipment. The synthesis process was mild and only needed only a short reaction time (7–10 min). As a simple example of the utilization of molecular oxygen under mild conditions, this method provides a novel way to synthesize benzimidazoles. The industrial synthesis of benzimidazoles may be realized by a cycle of microwave irradiation.     

Synthesis of Mono-and Di-fluorinated Benzimidazoles

Three efficient methods to synthesize mono‐ and di‐fluorinated benzimidazoles are reported. These methods provide 5‐amino‐6‐fluoro‐benzimidazoles ( 5 ), 5,7‐difluoro‐benzimidazoles ( 10 ), and 6‐fluoro‐benzimidazoles ( 13 ) starting from commercially available 1,5‐difluoro‐2,4‐dinitrobenzene (DFDNB), 2,3,4,5‐tetrafluoro‐6‐nitrobenzoic acid (TFNBA), and 2,4‐difluoro‐1‐nitrobenzene (DFNB), respectively.     

Cyclization of aromatic aldehydes and phenylenediamines under reduced pressure: A convenient,environmentally friendly,and simple procedure for benzimidazole precursors

The condensation of phenylenediamines with aromatic aldehydes in the presence of catalysts to obtain benzimidazoles under harsh condition is achieved by various reported conditions. The present work demonstrates a convenient, environmentally friendly, and simple procedure to obtain benzimidazoles through the cyclization between phenylenediamines and aromatic aldehydes under reduced pressure. By simply adding aromatic aldehydes to diaminobenzene derivatives and allowing the stoichiometric reaction at room temperature under reduced pressure at 66.6?Pa, the dehydrogenation leads to benzimidazoles with the yield as high as 80–90%. In addition, the purging of H₂ gas to benzimidazoles results in the hydrogenation of imidazole to obtain the intermediate benzimidazolidine form. This confirms how the cyclization relies on the reduced pressure. This synthesis pathway not only gives the aromatic aldehydes with high yield under the mild condition but also the selection of benzaldehydes with reactive functional groups leads to the precursors for other chemical modifications and polymerizations.     

1,2,3-benzotriazines. I. The synthesis of some benzimidazo [1,2-c][1,2,3]-benzotriazines and naphth[1′,2,(2′,1′):4,5]imidazo[1,2-c][1,2,3]benzotriazine

A number of substituted benzimidazo[1, 2-c][1,2,3]benzotriazines were prepared by the diazotization of the appropriate 2-(o-aminophenyl)benzimidazoles. Diazotization of 2-(o-aminophenyl)naphth[1,2-d]imidazole yielded a new heterocyclic ring system. Various methods of preparation of 2 - (o-aminophenyl)benzimidazoles were investigated. The condensation of o-phenylenediamines with anthranilic acids, in the presence of polyphosphoric acid, provided a convenient route to 2-(o-aminophenyl)benzimidazoles but in several cases the products were contaminated with considerable amounts of 6-(o-aminophenyl)benzimidazo[1,2 -c]quinazolines. 2 - (o-Aminophenyl)benzimidazoles were also obtained by the catalytic hydrogenation of 2-(o-nitrophenyl)benzimidazoles which resulted from the condensation of an o-phenylenediamine with an o-nitrobenzaldehyde in ethanol, nitrobenzene or acetic acid. When the condensation was carried out in nitrobenzene, small amounts of 2-(o-aminophenyl)benzimidazoles were also formed. The Weidenhagen synthesis, which involves the reaction of an aromatic diamine with an aldehyde in the presence of copper acetate and subsequent decomposition of the cuprous salt of the benzimidazole, yielded 2-(o-aminophenyl)benzimidazoles instead of the expected 2-(o-nitrophenyl)benzimidazoles when the decomposition was carried out in ethanol. When the cuprous salt was treated with hydrogen sulfide in dilute hydrochloric acid, a mixture of amino- and nitrobenzimidazoles resulted. The ultraviolet and infrared spectra of all the compounds prepared were examined.     

Synthesis of pyrazolo[1′,5′:1,2]-1,3,5-triazino[5,6-a]benzimidazoles

The synthesis of a new class of tetracyclic bridgehead heterocycle pyrazolo[1′,5′:1,2]-1,3,5-triazino[5,6-a] benzimidazoles is reported. The key intermediate 2-(3-aminopyrazol-2-yl)benzimidazoles were prepared by the reaction of 2-hydrazinobenzimidazole with an appropriate reagent such as ethyl ethoxymethylenecyanoacetate, ethoxymethylenemalononitrile, β-cyanoacetophenone or α-formylphenylacetonitrile. The treatment of these key intermediates with triethylorthoesters afforded the corresponding pyrazolo[1′,5′:1,2]-1,3,5-triazino[5,6-a]benzimidazoles.     

Synthesis of benzimidazole based JNK inhibitors

Substituted benzimidazoles were synthesised using a number of novel reactions, including displacement of a 2-sulfone group, preparation of 4-diazo benzimidazole derivatives and lithiation of benzimidazoles in the 4-position.     

Studies on the reaction of unsymmetrical trifluoromethyl 1,2-phenylenediamine with various ketones leading to novel fluorinated heterocycles

Unsymmetrical 1,2-phenylenediamine on reaction with various ketones resulted in a number of fluorinated heterocycles such as benzimidazoles, quinoxalines and spiro benzimidazoles in high yields. The role of substituents in diamine in its reaction with various ketones and on the nature of product formation has been studied in detail.     

An efficient method to access 2-substituted benzimidazoles under solvent-free conditions

An expeditious method to access 2-substituted benzimidazoles was developed. Both aromatic (phenols, anilines, and thiophenols) and alkyl nucleophiles (amines and thiols) react with 2-methylsulfonyl benzimidazole under solvent-free conditions to generate a variety of 2-substituted benzimidazoles.     

苯并咪唑及其衍生物合成与应用研究进展

苯并咪唑及其衍生物具有良好的生物活性, 而且是一种重要的药物中间体. 由于它们具有良好的生物活性和反应活性, 一直都是研究的热点. 从该类化合物的合成与应用两个方面综述了近年来该领域的重要研究成果.     

Novel trialkylsilyl(germyl)-substituted thienyl- and furylbenzimidazoles and their N-substituted derivatives – synthesis,structure and cytotoxic activity

The reaction of 1,2-phenylenediamine with a variety of silicon- or germanium-containing 2-furaldehydes or 2-thienylcarbaldehydes in DMFA gave the corresponding benzimidazole derivatives in moderate yields (36–49%) in the presence of sodium hydrogen sulfite. As a result, a new series of silyl, germyl substituted hetarylbenzimidazoles were synthesized and their in vitro cytotoxicity was studied. The quaternisation of N-substituted benzimidazoles by heating with various alkyl, allyl and propargyl chlorides and bromides leads to the formation of benzimidazolinium salts. Potential cytotoxic activity of synthesized new benzimidazoles and benzimidazolinium salts was tested in vitro on two monolayer tumour cell lines: MG-22A (mouse hepatoma), HT-1080 (human fibrosarcoma) and normal mouse fibroblasts (NIH 3T3) and compared with corresponding benzimidazoles.     

固相微萃取/高效液相色谱联用分析食品中痕量苯并咪唑

建立了整体柱固相微萃取/高效液相色谱-紫外联用方法用于食品中6种痕量苯并咪唑的分析。在三元溶剂(N,N-二甲基甲酰胺、对二甲苯和异辛烷)体系下,以4-乙烯基苯硼酸与乙二醇二甲基丙烯酸酯原位聚合法制备了4-乙烯基苯硼酸-乙二醇二甲基丙烯酸酯固相微萃取整体柱,并采用热重分析仪、红外光谱、电镜进行表征。分别研究了萃取溶剂、萃取流速、净化体积、解吸溶剂、解吸流速和解吸体积对富集量的影响。在优化条件下,该方法对苯并咪唑的富集倍数高达1 607~3 015倍,方法的线性范围为0.100~100μg/L,检出限为21~33 ng/L,相对标准偏差(RSD)不大于7.4%。采用该方法分析鱼肉、鸭肉、鸭血和鸭肝样品中的苯并咪唑,加标回收率为75.0%~118%,RSD为1.6%~8.7%。该方法灵敏、准确,能满足食品中痕量苯并咪唑的分析要求。     

A simple and efficient one step synthesis of benzoxazoles and benzimidazoles from carboxylic acids

Benzoxazoles or benzimidazoles can be rapidly and efficiently synthesized from a variety of carboxylic acids with 2-aminophenols or 1,2-phenylenediamines in one simple step, respectively. The use of commercially available PS-PPh₃ resin combined with microwave heating delivered a variety of benzoxazoles and benzimidazoles in high yields and purities.     

Evaluation of chromatographic columns packed with semi‐ and fully porous particles for benzimidazoles separation

The behavior of 15 benzimidazoles, including their main metabolites, using several C₁₈ columns with standard or narrow‐bore diameters and different particle size and type were evaluated. These commercial columns were selected because their differences could affect separation of benzimidazoles, and so they can be used as alternative columns. A simple screening method for the analysis of benzimidazole residues and their main metabolites was developed. First, the separation of benzimidazoles was optimized using a Kinetex C₁₈ column; later, analytical performances of other columns using the above optimized conditions were compared and then individually re‐optimized. Critical pairs resolution, analysis run time, column type and characteristics, and selectivity were considered for chromatographic columns comparison. Kinetex XB was selected because it provides the shortest analysis time and the best resolution of critical pairs. Using this column, the separation conditions were re‐optimized using a factorial design. Separations obtained with the different columns tested can be applied to the analysis of specific benzimidazoles residues or other applications.     

Iron-catalyzed one-pot synthesis of benzimidazoles from 2-nitroanilines and benzylic alcohols

The iron-catalyzed heterocyclizations from 2-nitroanilines and benzylic alcohols to form benzimidazoles using hydrogen transfer reaction were investigated in this study. In the presence of dppf in toluene at 150 °C, various benzimidazoles were obtained in moderate to good yields within 24 h. The reaction was proposed to proceed via a cascade of alcohol oxidation, nitro reduction, condensation, and dehydrogenation.     

3-α-Halocarbonyl derivatives of pyrazolo[1,5-a] benzimidazole and their reactions

3-(-haloacyl)-2,4-dialkylpyrazolo[1,5-a]benzimidazoles can be obtained either by brominating 3-acetylpyrazolo[1,5-a]benzimidazoles with bromine in acetic acid, or by acylating the 3-unsubstituted pyrazolobenzimidazoles with haloacetic halides. Halogenation of 3-acetylpyrazolo[1,5-a]benzimidazoles with bromine in acetic acid in the presence of sodium acetate, and bromination with N-bromosuccinimide or 1-chlorobenzotriazole, result in deacylation to give 3,6(7)-dibromo- and 3-chloropyrazolo[1,5-a]benzimidazoles. The mono- and trihaloketones obtained have been used to prepare the corresponding aminoketones, the 3-carboxylic acid, and its derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 43–48, January, 1988.     

Copper-catalyzed synthesis of 1,2-disubstituted benzimidazoles from imidoyl chlorides

A strategy for the synthesis of 1,2-disubstituted benzimidazoles has been developed and a variety of 1,2-disubstituted benzimidazoles were obtained from imidoyl chlorides and o-haloanilines via copper(I)-catalyzed reaction in moderate yields.     

Synthesis of 2-arylbenzimidazoles via microwave Suzuki-Miyaura reaction of unprotected 2-chlorobenzimidazoles

A series of 2-arylbenzimidazoles were synthesized via microwave-mediated Suzuki-Miyaura coupling of 2-chloro benzimidazoles and either arylboronic acids or aryltrifluoroborate salts. The most notable aspect of the present work is that there is no need for protection of the benzimidazoles. In addition, reaction conditions were optimized to reduce homo coupling of pyridylboronic acids.