Regioselective Formal [4 + 2] Cycloadditions of Enaminones with Diazocarbonyls through Rh^III-Catalyzed C-H Bond Functionalization

A regioselective formal [4 + 2] cycloaddition for the assembly of highly functionalized benzene rings was successfully developed. In this reaction, olefinic C-H bond functionalization/cyclization cascade reaction followed by rearomatization led to the desired molecules in one step under mild reaction conditions. This protocol also displays a broad substrate scope and good tolerance to a wide range of functional groups. Additionally, the potential utility for the synthesis of highly conjugated polybenzenes and diversification of natural products was also demonstrated.