C4-Selective C-H Borylation of Pyridinium Derivatives Driven by Electron Donor-Acceptor Complexes.

The photoinduced C4-selective C-H borylation of pyridines was achieved using electron donor-acceptor complexes derived from a Lewis base and N -amidopyridinium salts under external oxidant- and photocatalyst-free conditions. Notably, the nucleophilic character of phosphite-ligated boryl radicals enables addition of a radical to position C4 of pyridinium salts to afford C4-borylated heteroarenes that are otherwise difficult to obtain. This approach provides a versatile platform for the installation of both phosphite- and amine-coordinated boron groups on a series of pyridines under mild conditions, demonstrating excellent C4-positional selectivity for the pyridine scaffolds.