A Unified Approach to (E)- and (Z)-Olefins Enabled by Low-Valent Tungsten Catalysis

A positionally selective alkene isomerization in which modulation of the ligand environment of the homogeneous tungsten catalyst grants access to either the (E)- or (Z)-stereoisomer is described. Compared to previously reported alkene isomerization methods, this reaction offers exquisite chemo- and regioselectivity and is user friendly due to the use of a simple, commercial precatalyst and ligand. Preliminary mechanistic studies suggest that tungsten’s ability to adopt 7-coordinate geometry is crucial for stereoselectivity and that substrate directivity prevents over-isomerization to the conjugated alkene, as is commonly observed with other catalysts. These features allows for exclusive formation of β,γ-unsaturated carbonyl compounds that are otherwise difficult to prepare.