General Papers ARKIVOC 2007 (xiii) 150-154
p-TsOH Catalyzed synthesis of 2-arylsubstituted benzimidazoles
Han Xiangming, a,b Ma Huiqiang, a and Wang Yulu *a
aCollege of Chemical and Environmental Science, Henan Normal University, Xinxiang, 453007, Henan, P. R. China bDepartment of Chemisrty and Environmental Engineering, Pingyuan University, Xinxiang, 453003, Henan, P. R. China E-mail: wyl@henannu.edu.cn
Abstract
p-TsOH (20 mol%) was used to be a catalyst for the synthesis of 2-arylsubstituted benzimidazoles efficiently. Simple and convenient procedure, easy purification and shorter reaction time are the advantageous features of this method.
Keywords: Benzimidazole, synthesis, p-TsOH, arylaldehyde, o-phenylenediamine
Introduction
Benzimidazole derivatives exhibit significant activity against several viruses such as HIV,1 herpes (HSV-1),2 RNA,3 influenza,4a and human cytomegalovirus (HCMV)1. The widespread interest in benzimidazole-containing structures has promoted extensive studies for their synthesis. While many strategies are available for benzimidazole synthesis,7-16 there are two general methods for the synthesis of 2-substituted benzimidazoles. One is the coupling of phenylenediamines and carboxylic acids4b or their derivatives (nitriles, imidates, or orthoesters),5 which often requires strong acidic conditions, and sometimes combines with very high temperatures or microwave irradiation.6 The other way involves a two-step procedure that includes the oxidative cyclo-dehydrogenation of Schiff bases, which are often generated from the condensation of phenylenediamines and aldehydes. Various oxidative and catalytic reagents such as sulfamic acid,7 I2,8 DDQ,9 Air,10 Oxone,11 FeCl3·6H2O,12 In(OTf)3,13 Yb(OTf)3,14 Sc(OTf)3,15 KHSO4,16 IL,17 have been employed. Because of the availability of a vast number of aldehydes, the condensation of phenylenediamines and aldehydes has been extensively used. While many published methods are effective, some of these methods suffer from one or more disadvantages such as high reaction temperature, prolonged reaction time, and toxic solvents etc. Therefore, the discovery of mild and practicable routes for synthesis of 2-substituted benzimidazoles continues to attract the attention of researchers.
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