PEG-mediated catalyst-free expeditious synthesis of 2-substituted benzimidazoles and bis-benzimidazoles under solvent-less conditions

A wide variety of 2-substituted benzimidazoles and bis-benzimidazoles were synthesized in high yields by PEG-mediated catalyst-free synthesis under solvent-less conditions. The products were directly recrystallized from hot methanol. The reaction occurred giving excellent yields with low as well as high molecular weight PEGs.     

Rapid one-pot preparation of 2-substituted benzimidazoles from 2-nitroanilines using microwave conditions

A high yielding one-pot procedure for the generation of 2-substituted benzimidazoles directly from 2-nitroanilines by in situ reduction and cyclization using a microwave procedure is described.     

Benzazoles. 3*. Synthesis and arylsulfonylation of 2-substituted benzimidazoles

2-Alkylbenzimidazoles have been obtained from o-nitroaniline and aliphatic carboxylic acids by reductive cyclization. Interaction of the former with arenesulfonyl chlorides led to the synthesis of 2-alkyl-1-arylsulfonylbenzimidazoles, the yield of which depended on the structure of the substituent in position 2.     

Nanosized sulfated zirconia as solid acid catalyst for the synthesis of 2-substituted benzimidazoles

The condensation reaction of o-phenylenediamine and arylaldehydes was investigated in the presence of nanosized sulfated zirconia (SO ₄ ^2? -ZrO₂) as the solid acid catalyst. Nanosized SO ₄ ^2? -ZrO₂ was prepared and characterized by the XRD, FT-IR, and SEM techniques. The results confirm good stabilization of the tetragonal phase of zirconia in the presence of sulfate. Reusability experiments showed partial deactivation of the catalyst after each run; good reusability can be achieved after calcinations of the recovered catalyst before its reuse.     

Parallel synthesis of amino bis-benzimidazoles by multistep microwave irradiation

A multistep liquid phase synthesis of specifically functionalized bis-benzimidazoles is presented by the application of single-mode microwave irradiation technique. The sustained solubilizing power and stability of the PEG-ester derived from the commercially available 4-fluoro-3-nitrobenzoic acid has been successfully carried through 10 steps involving ipso-S_NAr reaction, neutral reduction and acid cyclization. All the steps in this synthetic sequence were assisted by microwave (MW) irradiation. The polymer support was cleaved to release the final head to tail bisbenzimidazoles in an efficient process.     

Liquid-phase synthesis of 2-substituted benzimidazoles, benzoxazoles and benzothiazoles

A novel acid fluoride for use in the liquid-phase synthesis of substituted benzimidazoles, benzoxazoles and benzothiazoles was developed. Its synthetic utility is exemplified by a structurally diverse set of aromatic heterocycles. Final cleavage is achieved by treatment with sodium methoxide in methanol for 12 h. The corresponding benzimidazoles, benzoxazoles and benzothiazoles were obtained in good isolated yields (22-62%, four steps).     

Synthesis and conversions of 2-substituted cinchoninic acid amides

Amides of 2-oxo- or 2-thiocinchoninic acid have been obtained by the reaction of substituted amides of 2-chlorocinchoninic acid with sodium acetate or sodium sulfide. The reaction of 2-thiocinchoninic acid amides with hydrazine hydrate or ethyl cyanoacetate leads to derivatives of 2-hydrazinocinchoninic acid or (4-carbamoyl-2-quinolyl)cyanoacetic ester respectively, which were also obtained from 2-chlorocinchoninic acid amides.Perm Pharmaceutical Academy, Perm 614600. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 697–700, May, 1997.     

Synthesis of some 7-substituted thiazolino [3,2-a] benzimidazoles

The 7-amino (IV) and 7-acetamido (I) derivatives of thiazolino[3,2-a]benzimidazole were synthesized. The IR spectra of I, its deutero derivative, and a number of intermediates were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 177–179, February, 1972.     

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.     

DBSA mediated chemoselective synthesis of 2-substituted benzimidazoles in aqueous media

An efficient synthetic method has been developed for the facile synthesis of 2-substituted benzimidazoles in organized aqueous media in the presence of a surfactant (viz. DBSA) as catalyst and I₂ as co-catalyst. The method described has the advantages of operational simplicity, excellent yields, high chemoselectivity, and clean and green reaction profile.     

Synthesis of benzimidazoles from o-phenylenediamines and DMF derivatives in the presence of PhSiH3

A simple approach to preparation of benzimidazoles from o-phenylenediamines and DMF derivatives, only employing PhSiH₃ as promoter without any other additives, was reported. This route provided moderate to high yields with a broad substrate scope. A plausible mechanism for the reaction is proposed based on the spectroscopic characterization (e.g., HRMS and ¹H NMR) of the reaction mixture.     

Combinatorial synthesis of biheterocyclic benzimidazoles by microwave irradiation

Liquid phasel synthesis of biheterocyclic benzimidazoles by controlled microwave irradiation was investigated. Polymer immobilized o-phenylenediamines was synthesized under microwave irradiation. The resulting PEG bound diamines was N-acylated with 4-fluoro-3-nitrobenzoic acid selectively in primary aromatic amino moiety. Nucleophilic aromatic substitution of amide was performed with various amines then cyclized to form the first benzimidazole scaffold in acidic condition. Successive reduction, cyclization with isothiocyanates yielded 5-(benzimidazol-2-yl)benzimidazoles. The desired products were released from the polymer support to afford the tri-substituted bis-benzimidazoles in good yields and purity.     

Conversion of sterically hindered diacylated 1,2-phenylenediamines into 2-substituted benzimidazoles

A series of bulky 2-substituted benzimidazoles was designed in order to find new leads for several biological targets. Formation by cyclodehydration from their monoacylated counterparts was shown to be strongly dependent upon the nature of the acyl group. In the case of a dicyclohexylmethyl group, cyclization was only observed in a p-toluenesulfonic acid/toluene mixture from the symmetrical diacylated precursor. Analysis of the mechanism was begun starting from mixed diacylated derivatives.     

Mild,one-pot preparation of 2-substituted benzimidazoles from organic halides

Alkyl halides are feasibly transformed into benzimidazoles by a domino reaction under solvent-free conditions. The organic halides react with o-phenylenediamines in stoichiometric amounts in the presence of pyridine-N-oxide to produce the desired substituted benzimidazoles. This domino synthesis does not require catalysts. The synthesis occurs in dry medium and the environmental impact is minimal. The method provides products without intermediate separation. A mechanism of benzimidazole synthesis is also proposed.     

Chemistry of 2-substituted benzimidazoles. 1. 5-Amino-2-methyl(aryl, arylalkyl, pyridyl)benzimidazoles

A series of 2-substituted benzimidazoles was synthesized. These products were consecutively converted into 5-nitro- and 5-amino-2-substituted benzimidazoles.Russian People's Friendship University, 117198 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 493–500, April, 200.     

Transmission of the substituent effects in 2-substituted benzimidazoles studied by 1H and 13C nuclear magnetic resonance

The substituent influence on the ¹H and ¹³C NMR chemical shifts in 2-substituted benzimidazoles and their anions and cations has been investigated. The transmission of the electronic effects of substituents from C-2 to C-5 (6) is approximately 20% less effective than that in the opposite direction. The solvent influence on the chemical shifts of protons and transmission effects in the charged forms of 2-substituted benzimidazoles has been studied.