Homoallylpinacolboronic Ester as Alkene Component in Cobalt-Catalyzed Alder Ene Reactions

A homoallylpinacolboronic ester has been applied in cobalt-catalyzed Alder ene reactions with 1-phenyl-1-propyne as the model alkyne to generate Alder ene intermediates with an allyl-boronate subunit. These intermediates are converted in situ with aldehydes in an allylboration reaction. The diastereoselectivity of the allylboration reaction is controlled via the Alder ene reaction, which generates the E-configured allylboronate subunit predominantly, thereby leading to the syn-allylboration product.