Redox-Neutral Vicinal Dialkylation of Aryl Boronic Esters via the Palladium/Norbornene Cooperative Catalysis.

Palladium/norbornene (Pd/NBE) cooperative catalysis has become an increasingly important tool for ipso/ortho difunctionalization of arenes; however, the ipso functionalization is primarily limited to coupling of a nucleophile or a π-system. Here, we report a new type of Pd/NBE-catalyzed difunctionalization reaction that simultaneously couples two alkyl electrophiles at the ipso and ortho positions of arenes. Diverse aryl boronic esters are employed as substrates. The redox-neutral feature of this reaction allows broad functional group tolerance. The synthetic utility is demonstrated in a streamlined preparation of a complex benzoazepane. Mechanistic studies reveal the potential involvement of an unusual radical-mediated ipso functionalization.