Palladium-Catalyzed meta-C-H Functionalization of Masked Aromatic Aldehydes

Palladium-catalyzed meta-C-H functionalization enabled by transient mediators has the potential to extend the utility of directed ortho-C-H functionalization to remote positions. However, there have been no reports of palladium-catalyzed meta-C-H functionalization of aromatic aldehyde derivatives, which are highly versatile intermediates in organic synthesis. Herein, we report the development of a directing group that, in the presence of a norbornene-derived mediator and an appropriate pyridone ligand, allows palladium-catalyzed meta-C-H functionalization of masked aromatic aldehydes. Mechanistic insight regarding the impact of the directing group length on this catalysis is also discussed.