Abstract
This paper describes the reaction of benzoylisothiocyanates with ortho -phenylenediamines forming the corresponding bisthioureas which undergo cyclization with elimination of thiocyanic acid on refluxing in pyridine leading to the format ion of 2-arylbenzimidazoles. The products have been characterized on the basis of satisfactor y analytical and spectral (IR, NMR, MS) data, and the mechanism of their formation is proposed.
Highlights
Benzimidazoles constitute a well-known class of five-membered azaheterocycles possessing different types of biological activity.[1]
We report 2:1 molar reactions of bezoylisothiocyanates with 1,2-phenylenediamines resulting into formation of corresponding bisthioureas which undergo cyclization to 2-arylbenzimidazoles by refluxing in pyridine
There is a report on formation of 2-N-(acyl)aminobenzimidazoles by the reactions of bezoylisothiocyanates with 1,2-phenylenediamines.[22]
Summary
Benzimidazoles constitute a well-known class of five-membered azaheterocycles possessing different types of biological activity.[1]. A three-component reaction of 2bromo/iodoaniline, aldehydes and sodium azide in the presence of CuCl-TMEDA has been reported to afford 2-arylbenzimidazoles.[16] Recently, non-conventional techniques such as microwave irradiation[17] and ultrasonic irradiation[18] have been employed to achieve easy. Joshi and coworkers have reported the synthesis of 2-arylbenzimidazoles by tetrabutylammonium fluoride mediated reaction of phenylene-1,2diamines with aromatic aldehydes in aqueous medium under the influence of ultrasonic irradiation.[18] Niknam and Fatehi-Raviz reacted phenylene-1,2-diamines with aromatic carboxylic acids in the presence of methylsulfonic acid over neutral alumina by microwave irradiation.[19]. There is a report on formation of 2-N-(acyl)aminobenzimidazoles by the reactions of bezoylisothiocyanates with 1,2-phenylenediamines.[22]
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