Modular Assembly of Ring-Fused and π‑Extended Phenanthroimidazoles via C–H Activation and Alkyne Annulation

π-Extension of 2-aryl-phenanthroimidazoles
via rhodium­(III)-catalyzed
C–H activation and alkyne annulation is developed. This method
enables rapid, practical and modular assembly of diverse ring-fused
phenanthroimidazoles, including an unusual rearrangement product using
aryl-alkyl asymmetric alkyne and a thiophene fused product which could
serve as a Fe3+ fluorescent probe. The feasibility of the
one-pot synthesis and ruthenium­(II)-catalyzed versions of this reaction
was also verified.