Base-mediated C4-selective C-H-sulfonylation of pyridine

The direct regioselective C-H-functionalization of simple, unfunctionalized pyridines is considered a long-standing challenge in heterocyclic chemistry. Herein, we report a novel one-pot protocol for the C4-selective sulfonylation of pyridines via triflic anhydride (Tf2O) activation, base-mediated addition of a sulfinic acid salt and subsequent elimination/rearomatization. Contrary to previous approaches employing tailored blocking groups, positional selectivity can be controlled by using N-methyl piperidine as simple, readily available external base. This method offers a highly modular and streamlined access to C4-sulfonylated pyridines