An Effective Synthetic Entry to Fused Benzimidazoles via Iodocyclization

A protocol for the synthesis of the fused heterocyclic polycyclic compounds pyrrole[1,2‐a]benzimidazoles, piperidine[1,2‐a]benzimidazoles and oxa‐fused benzimidazoles using iodine and silver nitrate by an exo‐dig or endo‐dig cyclization pathway at room temperature has been developed. Silver nitrate is a key additive for improving the yield, and the improvement is a result of this additive eliminating the influence of iodine ions (I−), which would otherwise lead to the formation of bis‐iodine by‐products. Cyclizations involving terminal and substituted alkynes were performed. Further functionalizations demonstrated that the iodo derivatives obtained are potential synthetic intermediates that can increase the molecular complexity.