Nickel-catalyzed electrochemical carboxylation of propargylic esters with CO₂ to 2,3-allenoic acids

Here, we report a novel nickel-catalyzed electrochemical carboxylation of propargylic esters with CO₂, characterized by the regioselective synthesis of 2,3-allenoic acids rather than propargylic carboxylic acids. Both acyclic propargylic esters and cyclic propargylic carbonates serve as effective substrates, facilitating the synthesis of mono-, di-, tri-, and tetra-substituted 2,3-allenoic acids with broad substrate scope under mild conditions. Mechanistic investigations indicate that the in situ generated Ni(I) complex might serve as the active species to react with propargylic esters, forming the allenyl-Ni(I) complex under electro-reductive conditions. A possible γ-selective nucleophilic attack of allenyl-Ni(I) complex on CO₂ is likely involved in the formation of the desired 2,3-allenoic acids.