Radical cyclisation onto imidazoles and benzimidazoles

New synthetic methodology has been developed for the synthesis of [1,2- a]fused imidazoles and benzimidazoles using intramolecular homolytic aromatic substitution. In the intramolecular substitution, N-(ω-alkyl) radicals are generated using Bu₃SnH from N-(ω-phenylselanyl)alkyl side chains. Phenylselanyl groups are used as radical leaving groups to avoid problems in the N-alkylation of imidazoles and benzimidazoles. Arylsulfones for imidazoles, and phenylsulfides for benzimidazoles, are used at the leaving groups in the homolytic substitutions.