Nickel-catalyzed alkyl-zincation and carboxylation of diynes
A nickel-catalyzed three-component carbo-carboxylation of aryl-substituted diynes with ZnR2 and CO2 is described. With an ortho-ester functionality in the aryl group as the directing group, the usually observed hydrocarboxylation is completely suppressed with an unexpected CC bond isomerization. Based on the X-ray diffraction analysis and mechanistic study, it is believed that the reaction started with the oxidative addition with an aryl-substituted C–C triple bond and transmetalation with dialkyl zinc, followed by syn-carbonickelation with an alkyl-substituted C–C triple bond. Subsequent reductive elimination afforded the corresponding sp2-carbon zinc intermediate. Finally, the dynamic isomerization of a zinc-linked CC bond and the subsequent exclusive reaction of an isomerized sp2-carbon zinc intermediate with CO2 afforded the final carboxylic acids with a high stereoselectivity.