Highly Stereo- and Regioselective Hydrocarboxylation of Diynes with Carbon Dioxide

A nickel-catalyzed three-component hydrocarboxylation of diynes with ZnEt₂ and CO₂ (1 atm) is disclosed. With this method, symmetric/nonsymmetric diynes could be reacted smoothly with very high stereo- and regioselectivity, affording conjugated 2,4-alkadienoic acids incorporated with five- or six-membered rings efficiently. A stepwise non-oxidative cyclometalation mechanism was proposed based on careful mechanistic studies