Cobalt-Catalyzed Hydroacylative Dimerization of Allenes Leading to Skipped Dienes.

A cobalt-diphosphine catalyst has been found to promote a selective 1:2 coupling reaction between aldehydes and allenes to form ß,δ-dialkylidene ketones, featuring skipped diene moieties, with high regioselectivities and stereoselectivities. The reaction is distinct from previously reported, rhodium-catalyzed aldehyde-allene 1:2 coupling to afford ß,γ-dialkylidene ketones bearing 1,3-diene moieties. The present hydroacylative dimerization involves a unique allene/allene oxidative cyclization mode to form a C1-C2 linkage between the allene molecules.