Regioselective C−H Hydroarylation of Internal Alkynes with Arenecarboxylates: Carboxylates as Deciduous Directing Groups

In the presence of catalytic [Ru(p‐cym)I2]2 and the base guanidine carbonate, benzoic acids react with internal alkynes to give the corresponding 2‐vinylbenzoic acids. This alkyne hydroarylation is generally applicable to diversely substituted electron‐rich and electron‐poor benzoic and acrylic acids. Aryl(alkyl)acetylenes react regioselectively with formation of the alkyl‐branched hydroarylation products, and propargylic alcohols are converted into γ‐alkylidene‐δ‐lactones. The hydroarylation can also be conducted decarboxylatively with a different choice of catalyst and reaction conditions. This reaction variant, which does not proceed via intermediate formation of 2‐vinylbenzoic acids, opens up a regioselective, waste‐minimized synthetic entry to vinylarenes. Make the switch: A simple ruthenium(II) complex catalyzes the regioselective hydroarylation of internal alkynes with benzoic acids. The conditions can be tuned to switch from a non‐decarboxylative to a decarboxylative pathway. Aryl(alkyl)acetylenes react regioselectively with formation of the alkyl‐branched 2‐vinylbenzoic acids, and propargylic alcohols cyclize to γ‐alkylidene‐δ‐lactones.