Direct Formic Acid Mediated Z-Selective Reductive Coupling of Dienes and Aldehydes.

Methods for the addition of unsaturated nucleophiles to carbonyls to generate Z-olefin products remain rare and often require either alkyl borane or zinc reductants, limiting their utility. Demonstrated here is that formic acid mediates the Rh-catalyzed, Z-selective coupling of dienes and aldehydes. The process is distinguished by broad tolerance towards reducible or electrophilic groups. Kinetic analysis suggests that generation of the catalytically active Rh intermediate by ligand dissociation is the rate-determining step. The rapid generation and trapping of Rh-allyl intermediates is key to preventing chain-walking isomerization events that plague related protocols. Insights gained through this study may have wider implications in selective metal-catalyzed hydrofunctionalization reactions.