Dual Co/Photoredox-Catalyzed Regio- and Stereoselective Synthesis of Highly Functional 1,3-Dienes

A dual Co/photoredox catalytic coupling of 1,3-enynes and α,ß-unsaturated aliphatic aldehydes and ketones has been developed that creates access to highly functional 1,3-diene synthons through a regio- and stereoselective carbon-carbon coupling process. The scope of the process features diverse functionalized scaffolds with a high degree of molecular complexity. The synthetic utility of these 1,3-dienes is demonstrated including a telescoped, one-pot approach using an alkynyl cyclic carbonate as a 1,3-enyne surrogate offering direct access to the 1,3-diene product. Mechanistic analysis involving control reactions, deuterium labeling studies and DFT calculations are in line with the in situ formation of a Co─H species and an outer-sphere coupling pathway in which a regio- and stereoselective coupling occurs between a dienyl radical and carbonyl species.