Unique dual‐emissive and deep‐blue/green fluorescent multi‐substituted 4‐azapyrenes with bathochromic shift emission, quantum yields up to 0.60 and long excited‐state lifetime were synthesized successfully by annulative π‐extension reactions. This synthesis constitutes a palladium‐catalyzed dehydrogenative annulation of N‐acyl‐2‐aminobiaryls with in situ 1,3‐diynes as a key step, giving substituted phenanthrenes via a rollover C−H bond activation, followed by Bischler‐Napieralski cyclization. Further π‐extension by superacid‐mediated cyclization produced a blue fluorescent naphtho 4‐azapyrene.
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.
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