Unprecedented Multicomponent Organocatalytic Synthesis of Propargylic Esters via CO2 Activation

Abstract

An efficient and straightforward organocatalytic method for the direct, multicomponent carboxylation of terminal alkynes with CO2 and organochlorides, towards propargylic esters, is reported for the first time. 1,3-Di-tert-butyl-1H-imidazol-3-ium chloride, a simple, widely-available, stable, and cost-efficient Nheterocyclic carbene (NHC) precursor salt was used as the (pre) catalyst. A wide range of phenylacetylenes, bearing electronwithdrawing or electron-donating substituents, react with allylchlorides, benzyl chlorides, or 2-chloroacetates, providing the corresponding propargylic esters in low to excellent yields. DFT calculations on the mechanism of this transformation indicate that the reaction is initiated with the formation of an NHCcarboxylate, by addition of the carbene to a molecule of CO2. Then, the nucleophilic addition of this species to the corresponding chlorides has been computed to be the rate limiting step of the process