Counterion Effects Enable Divergent Pd‐Catalyzed Carbonylative Cyclization of Amide‐Tethered o‐Alkynylphenols

The catalytic carbonylation of alkynes is a powerful route to heteroaromatic scaffolds, yet achieving regioselectivity remains challenging. Herein, we report a divergent carbonylative cyclization of 2-alkynylphenol derivatives that affords either coumarins (6-endo-dig) or 2-coumaranones (5-exo-dig) by tuning the palladium-based catalytic system. Pd(OAc)2 in combination with TFA favored coumarins formation with high yield and selectivity (>15:1), whereas electron-deficient species such as Pd(MeCN)4(BF4)2 promoted 2-coumaranones with up to 84% yield and >25:1 selectivity. While many approaches exploit ligand design to steer selectivity, these results highlight counterion effects as a powerful tool to control regioselectivity in palladium-catalyzed carbonylative cyclization, expanding the utility of alkyne carbonylation for the synthesis of biologically relevant heterocycles.