The reaction of o-benzofulvene with TfOH leads
to intramolecular cyclization through novel C–C and C–N
bond formation, resulting in the formation of 5H,10′H-spiro[benzo[k]phenanthridine-5,6′-dibenzopentalene].
This protocol provides a new molecular framework with reasonable to
excellent yields and tolerates various electron-withdrawing/donating
substituents. This method yields diastereoselectivity of up to >20:1.
Furthermore, it is free of bases, oxidants, and metals and proceeds
under mild reaction conditions, which are favorable for synthetic
organic chemistry.