Stereocomplementary Desymmetrizations of Divinylcarbinols by Zirconium(IV)- vs. Titanium(IV)-Mediated Asymmetric Epoxidations

Substituted Cs‐symmetric penta‐1,4‐dien‐3‐ols (“divinylcarbinols”) containing cis‐ or trans‐di‐substituted CC bonds were desymmetrized by asymmetric monoepoxidations. Sharpless conditions gave anti‐configured monoepoxides. For cis,cis‐divinylcarbinols this was unprecedented. Oxidation with tert‐butyl hydroperoxide (t‐BuOOH) in the presence of zirconium tetraisopropoxide [Zr(O‐i‐Pr)4] and a dialkyl tartrate led to the corresponding syn‐configured monoepoxides. Under the reaction conditions the ee of monoepoxide syn‐12 increased with time from 75 to 99% ee. The reason is the preferential overoxidation of its minor enantiomer. The ease of preparation and multitude of functional groups make epoxides 12–14 worthwhile building blocks for the synthesis of non‐racemic structures.