Electrophilic Cyclization of Aryldiacetylenes in the Synthesis of Functionalized Enediynes Fused to a Heterocyclic Core

An efficient strategy for the synthesis of asymmetrically substituted enediynes fused to benzothiophene, benzofuran, and indole was developed. The proposed approach is based on the electrophilic cyclization of diacetylenes and Sonogashira coupling. Thus, iodocyclization of readily available ortho-functionalized (buta-1,3-diynyl)­arenes was used as a direct way for the synthesis of 2-ethynyl-3-iodoheteroindenes. These substrates and their modified derivatives were easily converted by Sonogashira coupling with acetylenes to a variety of asymmetrically substituted acyclic enediynes fused to heterocycles. The tolerance of the developed methodology to a variety of functional groups is a great advantage in the synthesis of macrocyclic enediyne systems fused to a heterocyclic core. Synthesis of indole-fused 12-membered macrocyclic dienediyne was achieved using ring-closing metathesis as a key step.