Molecular iodine-mediated cascade reaction of 2-alkynylbenzaldehyde and indole: An easy access to tetracyclic indoloazulene derivatives

The synthesis of iodo-substituted tetracyclic indole fused azulene derivatives was achieved from the reaction of 2-(substituted phenylethynyl)-benzaldehydes and different indoles in the presence of molecular iodine. The reaction involves the formation of a bisindole from the corresponding 2-(substituted phenylethynyl)benzaldehyde and indole followed by iodocyclization in a one-pot cascade process. A wide range of 2-(substituted phenylethynyl)-benzaldehydes and indoles were utilized in this protocol to derive a diverse range of iodo-substituted tetracyclic indole fused azulene derivatives in moderate to good yields. Further functionalizations of the iodo-substituted tetracyclic indole fused azulenes were achieved by various palladium-catalyzed crosscoupling reactions to generate highly substituted tetracyclic indole fused azulene derivatives.