C–H Borylation Catalysts that Distinguish Between Similarly Sized Substituents Like Fluorine and Hydrogen

By modifying ligand steric and electronic profiles it is possible to C–H borylate ortho or meta to substituents in aromatic and heteroaromatic compounds, where steric differences between accessible C–H sites are small. Dramatic effects on selectivities between reactions using B2pin2 or 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin) are described for the first time. Judicious ligand and borane combinations give highly regioselective C–H borylations on substrates where typical borylation protocols afford poor selectivities.