‘One-pot’ nitro reduction–cyclisation solid phase route to benzimidazoles

An improved solid phase synthesis of benzimidazoles is described. A polymer-bound o-nitroaniline was reacted with aldehydes in DMF in the presence of SnCl2·2H2O at 60°C for three hours to give benzimidazoles in excellent purity and good yield after TFA cleavage. A library of 25 benzimidazoles was prepared using this ‘one-pot’ procedure.