Sterically Directed Functionalization of Aromatic C−H Bonds:  Selective Borylation Ortho to Cyano Groups in Arenes and Heterocycles

Ir-catalyzed borylations of 4-substituted benzonitriles are described. In contrast to electrophilic aromatic substitutions and directed ortho metalations, C-H activation/borylation enables functionalization at the 2-position, adjacent to the cyano group, when the 4-subsitutent is larger than cyano. When an excess of borane reagent is used, diborylation can be achieved with a single regioisomer being formed in certain cases. Extension of sterically directed borylation to cyano-substituted, five- and six-membered ring heterocycles is also reported.