Rh-catalyzed ortho-selective C-H borylation of N-functionalized arenes with silica-supported bridgehead monophosphine ligands.

Supported phosphine-Rh systems, prepared in situ from silica-supported bridgehead monophosphines and Rh(OH)(cod), have enabled ortho-selective C-H borylation for a range of arenes containing nitrogen-based directing groups. The regioselectivity was excellent with various N-directing groups, including saturated and unsaturated N-heterocycles, tert-aminoalkyl groups, and imine-type C-N double bonds. The reaction showed significant tolerance toward steric repulsion around the reacting C-H bond. This Rh catalysis complements the Ir-catalyzed ortho-borylation, which is effective for arenes with oxygen-based directing groups.