Electroreductive Carboxylation of Propargylic Acetates with CO 2 : Access to Tetrasubstituted 2,3-Allenoates.

An electroreductive carboxylation of propargylic alcohols with CO 2 and then workup with TMSCHN 2 to construct tetrasubstituted 2,3-allenoates is developed. This method allows the incorporation of an external ester group into the resulting allene system through electroreduction, carboxylation, and deacetoxylation cascades. Mechanistically, electricity on/off experiments and cyclic voltammetry analysis support the preferential generation of the CO 2 radical anion or the 3-aryl propargylic acetate radical anion based on the electron nature of the aryl rings.