Quaternary ammonium salts were synthesized in moderate to good yields through double oxidative C−H bond activation on azobenzenes. The mechanism of the highly regioselective reaction of 2‐azobiaryls with alkenes to give orange‐red‐fluorescent cinnolino[2,3‐f]phenanthridin‐9‐ium salts and 15H‐cinnolino[2,3‐f]phenanthridin‐9‐ium‐10‐ide is proposed to involve ortho C−H olefination of the 2‐azobiaryl compound with the alkene, intramolecular aza‐Michael addition, concerted metalation–deprotonation (CMD), reductive elimination, and oxidation.
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.
Quaternary ammonium salts were synthesized in moderate to good yields through double oxidative C−H bond activation on azobenzenes. The mechanism of the highly regioselective reaction of 2‐azobiaryls with alkenes to give orange‐red‐fluorescent cinnolino[2,3‐f]phenanthridin‐9‐ium salts and 15H‐cinnolino[2,3‐f]phenanthridin‐9‐ium‐10‐ide is proposed to involve ortho C−H olefination of the 2‐azobiaryl compound with the alkene, intramolecular aza‐Michael addition, concerted metalation–deprotonation (CMD), reductive elimination, and oxidation.
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