Synthesis of benzimidazoles in high-temperature waterThis work was presented at the Green Solvents for Catalysis Meeting held in Bruchsal, Germany, 13–16th October 2002.Electronic supplementary information (ESI) available: analytical data for compounds 3a–f and 5g–j. See http://www.rsc.org/suppdata/gc/b2/b212394k/

Abstract

The objective of this research was to conduct constructive organic chemistry in water and to achieve yields that were comparable to, or better than, those in conventional media. The synthesis of 2-phenylbenzimidazole from 1,2-phenylenediamine and benzoic acid was chosen as a benchmark reaction. The reaction parameters, such as temperature, density and reaction time, have been systematically studied to understand whether the solvent properties of high-temperature water can have a positive effect on the chemistry. The reaction was performed in a new design of batch-type autoclave and was also monitored in situ by UV-vis spectroscopy. By tuning the parameters, the yield has been optimised to around 90%. The optimised conditions were then applied to related benzimidazoles, some of which crystallised from solution in situ to yield single crystals that were sufficiently pure to be analysed directly by X-ray diffraction, without any further purification. JHC This journal is

Simple, Mild, and Highly Efficient Synthesis of 2-Substituted Benzimidazoles and Bisbenzimidazoles

“…As indicated in the literature, their synthesis by conventional heating required prolonged reaction times [32][33][34] and harsh conditions such as high temperatures, 20 high pressures, 20 and toxic solvents. [33][34][35] In this study, the synthesis was performed in short times (e.g., 10 min for compound 33) with good yields (80-92%) under mild (MW/180 W) and solvent-free conditions.…”

“…One method is condensation of o-phenylenediamines with corresponding carboxylic acids via a strong acid, [12][13][14][15] PPA, [15][16][17] or a catalyst. 18,19 High-temperature-pressurised systems 20 or microwaves (MWs) 17,18 are also used to promote these reactions. The other method is condensation of o-phenylenediamines with aldehydes under oxidative conditions.…”

An efficient and versatile synthesis of 2, 2'-(alkanediyl)-bis-1H-benzimidazoles employing aqueous fluoroboric acid as catalyst: density functional theory calculations and fluorescence studies

“…Proton transfer probably takes place in the excited state, yielding a highly conjugated species that fluoresces at a longer wavelength. 7,15 It cannot be due to tautomerisation, because different tautomeric forms are possible in all these bis-benzimidazole compounds. The extensive conjugation is absent for compounds 4q, 4n and 4l; both the absorption and fluorescence band maxima are blue-shifted as compared to compound 4a.…”

Chemoselective Synthesis of 2-Aryl-1-arylmethyl-1H-benzo[d]imidazoles Using Indion 190 Resin as a Heterogeneous Recyclable Catalyst

“…A number of improved methods have been developed for the synthesis of benzimidazoles involves a reaction between an o-phenylendiamine and a carboxylic acid or its derivative (nitrile, amidate and orthoester) under harsh dehydrating condition. [14][15][16][17] The most popular strategies for the synthesis of 1,2-disubstitted benimidazoles include N-alkylation of 2-substituted benimidazole in the presence of strong base, 18,19 N-alkylation of o-nitroanilides followed by a reductive cyclization, 20,21 cyclocondensation of N-substituted o-aminoanilides, 22 and the condensation of N-substituted phenylenediamine with sodium salt of α-hydroxy benzylsulphonic acid. 23 In addtion, 1,2-disbstituted benzimidazoles are also be accessed by direct one-step condensation of o-phenylenediamines with aldehydes by involving the influence of different acid catalysts under various reaction conditions [24][25][26][27][28][29][30][31][32][33] or by using polymer-supported hypervalent iodine (PDIAS) as a reagent.…”