Regiodivergent Arylation of Pyridines via Zincke Intermediates.

An arylation protocol for pyridines is described, via the ring-opened Zincke intermediate. Treatment of pyridines with triflic anhydride and a secondary amine produces an azahexatriene species, which undergoes regioselective Pd-catalyzed arylation at the putative C4 position. Recyclization then provides the pyridine products. Alternatively, metal-free arylation with a diaryliodonium salt is selective for the pyridine meta-position, affording a regiodivergent approach to pyridine biaryls from a common intermediate.