Metal‐Free Oxidative Cross Coupling of Indoles with Electron‐Rich (Hetero)arenes

A new method for the synthesis of bi‐heteroaryls is reported, based on the umpolung of indoles with benziodoxol(on)e hypervalent iodine reagents (IndoleBX). The oxidative coupling of IndoleBX with an equimolar amount of electron‐rich benzenes, indoles, pyrroles, and thiophenes proceeded under mild transition‐metal‐free conditions. Functionalized non‐symmetrical bi‐indolyl heterocycles were accessed efficiently. Introduction of a new type of C2‐substituted indole benziodoxole reagents further allowed extending the scope of the reaction to NH unprotected and C3‐alkylated indoles. The obtained bi‐heterocycles are important building blocks in synthetic and medicinal chemistry, and could be easily transformed into more complex heterocyclic systems. Smooth umpolung: The use of stable Indole‐BenziodoXol(on)e (IndoleBX) hypervalent iodine reagents allows oxidative coupling of electron‐rich (hetero)arenes under mild metal‐free conditions to access hetero‐bi‐heterocycles in high yields. High functional group tolerance set the stage for easy and regioselective post‐functionalization to access more complex heterocyclic systems.