Ion Pair-Directed Regiocontrol in Transition-Metal Catalysis: A Meta-Selective C–H Borylation of Aromatic Quaternary Ammonium Salts

The
use of noncovalent interactions to direct transition-metal
catalysis is a potentially powerful yet relatively underexplored strategy,
with most investigations thus far focusing on using hydrogen bonds
as the controlling element. We have developed an ion pair-directed
approach to controlling regioselectivity in the iridium-catalyzed
borylation of two classes of aromatic quaternary ammonium salts, leading
to versatile meta-borylated products. By examining a range of substituted
substrates, this provides complex, functionalized aromatic scaffolds
amenable to rapid diversification and more broadly demonstrates the
viability of ion-pairing for control of regiochemistry in transition-metal
catalysis.