Synthesis of Fluorescent 4‐Azapyrenes by Palladium(II)‐Catalyzed Dual C−H Bond Activation and Annulation

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.