Control of the Regioselectivity in Cobalt- versus Ruthenium-Catalyzed Alder-ene Reaction of Unsymmetrical 1,3-Diynes

The Alder-ene reaction of trialkylsilyl-substituted 1,3-butadiynes with terminal alkenes was investigated utilizing a cobalt-based catalyst, and the results were compared with Alder-ene rections catalyzed by the [CpRu(H3CCN)(3)]PF6 catalyst. Obviously, the two catalysts gave complementary results of yn-dienes differing in the site where the new carbon carbon bond was formed. Of particular interest are observations concerning the double bond migration within the alkene component. While simple alkenes gave exclusively the E-configuration, the application of 3-buten-1-ol resulted in the corresponding Z-double bond, indicating that the hydroxyl group acts as donor coordinating to the cobalt center and thereby altering the reaction pathway.