Synthesis of Condensed Benzo[N,N]-Heterocycles by Microwave-Assisted Solid Acid Catalysis

Abstract

The synthesis of several types of condensed benzo[N,N]-heterocycles such as benzimidazoles, benzodiazepines, quinoxalinones by a microwave-assisted solvent-free solid acid catalyzed method is described. The commercially available, inexpensive K-10 montmorillonite is an excellent catalyst for the synthesis of the target compounds. Our approach is based on the reactions of a wide variety of o-phenylenediamines, with ketones, aldehydes and bifunctional reagents, respectively. The cyclization reactions were initiated by microwave irradiation. The products, in most cases, were obtained in very high yields (up to 98%) and excellent selectivities in very short reaction times. The effective combination of solid acid catalysis, solvent-free conditions and microwave irradiation provides an attractive and highly ecofriendly approach for the synthesis of these important heterocycles.

Environmentally benign, microwave-assisted chemoselective N-hydroxyalkylation of indoles with trifluoroacetaldehyde methyl hemiacetal

“…25 However, our recent mechanistic and DFT investigations showed that the outcome of this hydroxyalkylation reaction is highly dependent on the choice of the reaction conditions, especially the selection of the solvent. 41 It was found that the use of non-polar solvents, such as hexane, resulted in the exclusive hydroxyalkylation at the C3 position. As the polarity of the solvent increases, the reaction tends to favor the formation of the N-alkylated product.…”

Synthesis, characterization and crystal structure of 2-(4-(methylthio)phenyl)-1H-benzo[d]imidazole

“…In addition, benzimidazole derivatives are effective against the human cytomegalovirus (HCMV) [5] and are also efficient selective neuropeptide Y Y1 receptor antagonists [6]. Most of the described methods for the synthesis of benzimidazoles make use of volatile organic solvents and involve solid-phase synthesis via o-nitroanilines [7][8][9][10] or the condensation of o-phenylenediamines with carboxylic acid derivatives [11], aldehydes [12][13][14][15][16][17] and aryl halides [18].…”

Acetic acid-promoted condensation of o-phenylenediamine with aldehydes into 2-aryl-1-(arylmethyl)-1H-benzimidazoles under microwave irradiation

“…Traditionally, the synthesis of benzimidazoles involves the condensation of o-phenylenediamine with aldehydes, [11][12][13] and carboxylic acids or their deriva-1182 AZARIFAR et al tives (nitriles, amidates, orthoesters) under harsh dehydrating conditions. [14][15][16][17][18][19][20] Benzimidazoles have also been prepared on a solid-phase to provide a combinatorial approach.…”