Tungsten-catalyzed stereodivergent isomerization of terminal olefins

Abstract

Catalytic alkene isomerization is a powerful synthetic strategy for preparing valuable internal alkenes from simple feedstocks. The utility of olefin isomerization hinges on the ability to control both positional and stereoisomerism to access a single product among numerous potential isomers. Within base-metal catalysis, relatively little is known about how to modulate reactivity and selectivity with group 6 metal-catalyzed isomerization. Here, we describe a tungsten-catalyzed, positionally selective alkene isomerization reaction in which tuning the ligand environment grants access to either the E- or Z-stereoisomer. The reactions employ simple, commercially available precatalysts and ligands. Preliminary mechanistic studies suggest that the ligand environment around 7-coordinate tungsten is crucial for stereoselectivity, and that substrate directivity prevents over-isomerization to the conjugated alkene. These features allow for exclusive formation of β,γ-unsaturated carbonyl compounds that are otherwise difficult to prepare.