β-Cyclodextrin-promoted synthesis of 2-phenylbenzimidazole in water using air as an oxidant

β-Cyclodextrin-promoted conversion of o-phenylenediamine and benzaldehyde to 2-phenylbenzimidazole is described using air as an oxidant. Various factors including reaction temperature, amount of β-cyclodextrin, different feed sequences and different steric hindrances of benzaldehydes were investigated. The observed results are rationalized on the basis of binding modes of inclusion of substrates inside the β-cyclodextrin cavity and find strong support from energy minimization studies and 1H NMR. In this paper β-cyclodextrin blocked the smooth conversion while enhanced the selectivity. This is the first example to use β-cyclodextrin as a catalyst in water to restrain the conversion while improving the selectivity.