It is important to achieve diverse functionalization of tertiary anilines due to their importance in biological molecules, pharmaceutical, functional materials, and ligands. A straightforward Pd/Cu-catalyzed oxidative C–H bond activation/N-dealkylative carbonylation of tertiary [1,1′-biphenyl]-2-anilines towards the synthesis of various biologically important phenanthridin-6(5H)-ones has been developed. A wide range of functional groups are well tolerated in this transformation. Moreover, O₂ is utilized as the terminal oxidant to promote the oxidative carbonylation process.