Copper-Catalyzed Annulation of Electrophilic Benzannulated Heterocycles with 2-Aminopyridine and 2-Aminoquinoline: Direct Access toward Polyring-Fused Imidazo1,2-apyridines

We have developed a direct method for the synthesis of polyring-fused imidazo1,2-apyridines via a copper-catalyzed annulation of electrophilic benzannulated heterocycles with 2-aminopyridine and 2-aminoquinoline. From 3-nitroindoles and 2-aminopyridine, we could synthesize tetracenes, viz., indole-fused imidazo1,2-apyridines, and by starting from 2-aminoquinoline, we could generate pentacenes, viz., indolo-imidazo1,2-aquinolines. In addition, we could also extend the methodology toward the synthesis of benzothieno-imidazo1,2-apyridines starting from 3-nitrobenzothiophene. Furthermore, the basic photophysical properties of these synthesized heteroacenes were evaluated.