Alkylative carboxylation of ynamides with CO2 and dialkylzinc reagents using a N‐heterocyclic carbene (NHC)–copper catalyst has been developed. A variety of ynamides, both cyclic and acyclic, undergo this transformation under mild conditions to afford the corresponding α,β‐unsaturated carboxylic acids, which contain the α,β‐dehydroamino acid skeleton. The present alkylative carboxylation formally consists of Cu‐catalyzed carbozincation of ynamides with dialkylzinc reagents with the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO2. Dialkylzinc reagents bearing a β‐hydrogen atom such as Et2Zn and Bu2Zn still afford the alkylated products despite the potential for β‐hydride elimination. This protocol would be a desirable method for the synthesis of highly substituted α,β‐ dehydroamino acid derivatives due to its high regio‐ and stereoselectivity, simple one‐pot procedure, and its use of CO2 as a starting material.