Hydrocarboxylation of alkynes utilizing CO2 as C1 synthon: A facile and environmentally benign access to α,β-unsaturated carboxylic acids

Traditionally, alpha,beta-unsaturated carboxylic acids have been prepared by utilization of named reactions such as the Wittig reaction, Doebner - Knoevenagel reaction, and Homer - Wadsworth - Emmons reaction. However, most of these protocols, if not all, suffer from restricted substrate scope, low levels of regio- and stereoselectivity and/or generation of a large amount of waste streams. Thus, the development of a convenient and efficient protocol for the regio- and stereocontrollable synthesis of the titled compounds using low-cost and easily accessible starting materials remains a big challenge. Recently, hydrocarboxylation of alkynes by employing carbon dioxide (CO2) was developed in the presence of various metal catalysts which allow the synthesis of alpha,beta-unsaturated carboxylic acids, with the benefits of high atom economy, high product yield and good regio- and stereoselectivity. The purpose of this review is to provide an overview of the recent progress and developments in this appealing synthetic procedure, with an emphasis on the mechanistic aspects of the reactions.