文摘
New methodology for the selective cross-metathesis (CM) of terminal olefins employing rutheniumbenzylidene 1 is described.1 CM with symmetric internal olefins was found to provide a useful means forhomologating terminal olefins to protected allylic alcohols, amines, and esters. Due to the limited commercialavailability of symmetric internal olefins, a two-step CM procedure was developed in which terminal olefinswere first homodimerized prior to the CM reaction. Terminal olefins with allylic methyl substituents wereobserved to provide CM products in diminished yield albeit with markedly improved trans-selectivity. Reactionrates were measured for CM reactions utilizing butenediol and allyl alcohol derivatives, and the resultsdemonstrated distinct advantages in reaction rate and stereoselectivity for reactions employing the disubstitutedolefins. In the course of studies of substrates with allylic oxygen substituents, a new CM application wasdiscovered involving the metathesis of acrolein acetal derivatives with terminal olefins. Acrolein acetals,including asymmetric variants derived from tartaric acid, proved to be exceptionally robust and trans-selectiveCM substrates. In related work, a pinacol-derived vinyl boronate was also found to be a reactive CM partner,providing a novel means for converting terminal olefins into precursors for the Suzuki coupling reaction.
