Synergistic Copper/Palladium Catalysis for the Regio- and Stereoselective Synthesis of Borylated Skipped Dienes

A Cu/Pd-catalyzed allylboration of alkynes with allyl carbonates and bis(pinacolato)diboron to afford borylated skipped dienes is reported. Synergistic Cu and Pd catalysis enables this protocol to work for a wide array of alkynes and allyl carbonates under mild conditions with total regio- and stereocontrol. This transformation features the catalytic generation of β-borylalkenylcopper intermediates and their use in Pd-catalyzed allylic substitution of allyl carbonates. The utility of this method is highlighted by the synthesis of (Z,E)-α-homofarnesene (pheromone) and the terpenoid precursor of Merochlorins (potent antibiotic agents).