Redox-Neutral ortho Functionalization of Aryl Boroxines via Palladium/Norbornene Cooperative Catalysis.

Palladium/norbornene (Pd/NBE) cooperative catalysis, also known as the Catellani reaction, has become an increasingly useful method for site-selective arene functionalization; however, certain constraints still exist due to its intrinsic mechanistic pathway. Herein we report a redox-neutral ortho functionalization of aryl boroxines via Pd/NBE catalysis. An electrophile, such as carboxylic acid anhydrides or O-benzoyl hydroxylamines, is coupled at the boroxine ortho position, and a proton as the second electrophile is introduced at the ipso position. This reaction does not require extra oxidants or reductants, and avoids stoichiometric bases or acids, thereby tolerating a wide range of functional groups. In particular, orthogonal chemoselectivity between aryl iodide and boroxine moieties is demonstrated, which could be used to control reaction sequences. Finally, a deuterium labelling study supports the ipso-protonation pathway. This unique mechanistic feature could inspire the development of a new class of Pd/NBE-catalyzed transformations.