Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide

Abstract

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. CO2 incorporation with alkylation: Alkylative carboxylation of ynamides with CO2 and a dialkylzinc reagent has been achieved by using a N-heterocyclic carbene (NHC)-copper complex as the catalyst. The reactions proceeded by Cu-catalyzed carbozincation of ynamides with dialkylzinc reagents and the subsequent carboxylation of the resulting alkenylzinc species (see scheme).