Synthesis of a Novel Library of 1-Substituted Pyrido[1,2-a]benzimidazoles

The reactivity and synthesis of new analogues of pyrido[1,2-a]benzimidazoles have been explored. Twenty-three derivatives bearing phenoxy, thiophenoxy, aniline, and aryl groups at the 1-position were successfully synthesised in 25-91% yield, via nucleophilic substitution, Buchwald-Hartwig amination, and Suzuki coupling type processes. Solvent free synthetic protocols were employed to achieve the nucleophilic substitution of anilines with electron donating groups or moderately electron withdrawing groups on a sterically demanding intermediate (7a). An unusual polycyclic heterocycle was identified as a side-product during this work: a dimeric bis(pyrido[1,2-a]benzimidazole).