Unveiling the Synthesis of Indole-Fused Eight-Membered Aza-Heterocycles via FeCl3–Catalyzed Radical C–N Coupling and Photophysical Studies

A novel strategy toward construction of indole-fused eight-membered heterocyclic rings through a radical pathway has been reported. Our approach involves tandem radical cyclization via FeCl₃-catalyzed cross-dehydrogenative double C–N bond formation using DDQ as an oxidant under mild condition. An EPR experiment and time course ¹H NMR study confirm that the addition of DDQ triggers the formation of pyrazole N-radical, which contributes to the formation of an indole-fused eight-member framework with a good yield. The structural diversity and synthetic utility have been explored, along with photophysical properties of the synthesized compounds.