Pd(II)‐Catalyzed Selective [4+2] Benzannulations of Pyridones with Alkenes: Diversity‐Oriented Synthesis of a Novel Fluorescent Quinolinone

Comprehensive Summary Herein, an intermolecular palladium(II)‐catalyzed regioselective [4+2] benzannulation reaction capable of converting 2‐pyridones into quinolinones was developed using electron‐deficient alkenes as two‐carbon units. An examination of the reaction mechanism indicated that the extension from 2‐pyridone to quinolinone was likely facilitated through a series of sequential C—H activation reactions or 6π electrocyclization, culminating in dehydrogenative aromatization. This method of diversity‐oriented synthesis of quinolinone derivatives is characterized by a broad substrate scope, atom economy, and excellent chemical selectivity. In addition, these quinolinone derivatives exhibit fluorescent absorption within the visible‐light spectrum, which makes them suitable candidates for the development of innovative fluorescent probes.