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

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.