An Effective Synthetic Entry to Fused Benzimidazoles via Iodocyclization

Xu Zhang, Yu Zhou, Hengshuai Wang, Diliang Guo, Deju Ye, Yungen Xu,
Hualiang Jiang, Hong Liu

Abstract: A protocol for the synthesis of the fused heterocyclic polycyclic compounds pyrroleACHTUNGTRENNUNG[1,2- a]benzimidazoles, piperidineACHTUNGTRENNUNG[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 addi- tive 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 deriv- atives obtained are potential synthetic intermedi- ates that can increase the molecular complexity.

Keywords : cyclization ; fused benzimidazoles ; iodine; silver nitrate