Carboxylic Acid Synthesis from Carbon Dioxide via First-Row Transition-Metal Catalysis and Copper-Promoted C(SP3)–H Functionalization

A general method for direct synthesis of aromatic carboxylic acids from aryl iodides and carbon dioxide was developed in our research group. The method uses copper(I) iodide as a catalyst in presence of inexpensive bidentate amine ligands, at mild temperatures under atmospheric pressure of carbon dioxide. The mild reaction conditions allow unparalleled reaction scope with excellent functional group tolerance. The compatible functional groups include bromide, chloride, fluoride, ester, ether, and carbonyl functional groups. Moreover, aryl iodides bearing unprotected amino and hydroxyl groups were also carboxylated for the first time. The methods works well even for hindered aryl iodides. A reaction mechanism was proposed based on the identification of copper(0) species involvement. Additionally, a method for cobalt-catalyzed direct carboxylation of allyl chlorides with carbon dioxide has been developed. The reactions work well at very mild conditions allowing highly selective synthesis of branched β,γ-unsaturated carboxylic acids.

Furthermore, a method for copper-mediated oxidative cross-coupled annulation of non-activated C(sp3)–H bonds with terminal alkynes has been developed. The reaction uses a removable auxiliary and an inexpensive copper promoter in the presence of base and silver salt oxidant. This approach is highly useful for 5-methylene-pyrrolidin-2-one synthesis. Moreover, the reaction conditions for copper-catalyzed nitronate and enolate homodimerizations under an oxygen atmosphere were optimized. The control experiments were performed to confirm the role of catalyst and oxygen.