Copper‐Catalyzed, Strain‐Promoted Synthesis of Imidazo[1,2‐ f ]phenanthridiniums from Cyclic Diaryliodonium Salts

A highly efficient copper‐catalyzed method has been developed for constructing valuable imidazo[1,2‐ f ]phenanthridinium derivatives from readily available imidazoles and torsionally strained cyclic diaryliodonium salts. Notably, this protocol is suitable for the late‐stage functionalization of imidazole motifs in complex drug molecules. Mechanistic studies indicate that the reaction proceeds via a tandem strain‐promoted ring‐opening/intramolecular cyclization sequence.