Cadmium chloride (CdCl2): a mild and efficient catalyst for the synthesis of benzimidazoles

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One-pot synthesis of benzimidazoles has been carried out using ortho-phenylenediamine and aldehydes. The condensation reaction smoothly took place in the presence of a mild Lewis acid cadmium chloride. All the reactions were carried out in acetonitrile at 80°C to 85°C. One-pot synthesis of benzimidazoles has been carried out using ortho-phenylenediamine and aldehydes. The condensation reaction smoothly took place in the presence of a mild Lewis acid cadmium chloride. All the reactions were carried out in acetonitrile at 80°C to 85°C.

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Publié le 01 janvier 2012
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Sammaiahet al. International Journal of Industrial Chemistry2012,3:11 http://www.industchem.com/content/3/1/11
R E S E A R C HOpen Access Cadmium chloride (CdCl2): a mild and efficient catalyst for the synthesis of benzimidazoles * B Sammaiah, D Sumalatha, GS Satyanarayana Reddy, M Rajeswari and LN Sharada
Abstract Onepot synthesis of benzimidazoles has been carried out using orthophenylenediamine and aldehydes. The condensation reaction smoothly took place in the presence of a mild Lewis acid cadmium chloride. All the reactions were carried out in acetonitrile at 80°C to 85°C. Keywords:Benzimidazoles, Aldehydes, Orthophenylenediamine, Cadmium chloride
Backgroundtriflate, ionic liquid, heteropoly acid, BDSB [3136], Molecules having benzimidazole as a basic structuralproline, solidsupported catalysts, polymersupported unit are known to exhibit a wide range of biologicalcatalysts and microwavepromoted [3741] reactions properties [13]. The potency and wide applicability ofhave been reported in the literature. imidazole pharmacophore can be attributed to its hydrogenUnfortunately, many of these methods suffer from bond donor/acceptor capability as well as its high affinitydrawbacks such as drastic reaction conditions [14], for metals, which are present in many protein active siteslow yields [16], tedious workup procedures [22] and [46]. The benzimidazole molecular skeleton is found in acooccurrence of several side reactions [20]. As a number of clinical therapeutic agents such as anticancer,consequence, the introduction of an efficient and mild antiulcerative, antihypersensitive, antiviral, antifungal, antimethod is still needed to overcome these limitations. tumor and antihistaminic [79] (Figure 1). The synthesis of benzimodazoles and its derivatives occupies pivotal position in the field of organic synthesis. In this contest, severalMethods efforts have been developed for the synthesis of benzimida zole derivatives. One of the most common methods for theResults and discussion preparation of benzimidazole derivatives involves the conHerein, we report a simple and efficient protocol for the densation of arylenediamines and carbonyl compoundssynthesis of benzimidazoles using the catalyst cadmium such as aldehydes and acid derivatives [1012]. Thecon chloride.In a preliminary study, we have examined the densation of phenylene diamine and carboxylic acidreaction of 1,2phenylenediamine or orthophenylenedi (derivatives) often requires strong acidic conditionsamine (OPD) (1 in Scheme 1) and benzaldehyde (2 in and/or high temperature [1318]. The other wayScheme 1) in the presence of cadmium chloride to involves the oxidative cyclodehydrogenation of Schiffoptimize the reaction conditions. The optimal conditions bases, which is generated from phenylene diamine andwere found to involve the use of OPD and aldehydes in 1:1 aldehyde in the presence of various oxidative andmolar ratios, with the catalyst loading of 10 mol% in aceto catalytic reagents. This is the most popular approachnitrile at 80°C to 85°C. As per the optimized conditions, in general for the synthesis of benzimidazole derivathe OPD and benzaldehyde reaction was completed within 3 h to give the corresponding product of 2phenylbenzimi tives. The reagents are CAN, K3PO4, oxone, sulfamic dazole (3a) in excellent yield, as shown in Scheme 1. acid, DDQ, PhI(OAc)2, iodine and KHSO4[1924]. In addition, several catalysts such as metal halides andEncouraged by the result obtained with benzaldehyde metaloxychlorides [2530], metal oxides, PTSA, metaland OPD, the method was applied to various aldehydes to establish the generality of the protocol. As shown in the Table 1, aromatic, heteroaromatic,α andβunsatur * Correspondence: sumalathadandu@yahoo.com Department of Chemistry, Osmania University, Koti, Hyderabad 500195, Indiaated aldehyde and aliphatic aldehydes reacted very well © 2012 Sammaiah et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.