ChemInform Abstract: Carboxylation of N—H/C—H Bonds Using N‐Heterocyclic Carbene Copper(I) Complexes.

Abstract

Transition-metal-mediated carboxylation of N H and C H bonds represents a nascent area in organic chemistry, because these reactions enable the efficient construction of valuable synthons. Palladium-catalyzed N-carbonylation–oxidation sequences are well-documented, but they often require high catalyst loadings and the use of either gaseous carbon monoxide or Group VI metal–carbonyl complexes. An analogous transformation sequence is also promoted by molybdenum and tungsten carbonyl amine species under forcing temperatures. Important advances in C-carboxylation reactions have been made using ruthenium and nickel complexes; however, examples under mild conditions are elusive. The carboxylation of allylstannanes, organozincs, and organoboronic esters have been described as a new method to improve functional group tolerance, but the stoichiometric consumption of an organometallic reagent remains a disadvantage. The reactivity of allylstannanes and organozinc compounds necessitates handling under an inert atmosphere, while organoboronic esters are expensive. A protocol has recently been developed for the C-carboxylation of simple aromatic groups under very mild reaction conditions. In this case the strongly basic [Au(IPr)(OH)] (IPr=1,3-bis(diisopropyl)phenylimidazol-2-ylidene) complex (pKaDMSO= 30.3(2)) was used, [11] which contains an N-heterocyclic carbene (NHC) ligand [Eq. (1)].