Crotylzirconium derivatives as a new reagent for the threo selective synthesis of β-methylhomoallyl alcohols

Crotylzirconium derivatives, prepared from the reaction of crotylmagnesium chloride or crotyllithium with bis (cyclopentadienyl) zirconium dichloride, undergo a rapid reaction with aldehydes to afford the threo product predominantly. The ratio of Cram/anti-Cram product via this reagent is ca. $\text{75}\text{25}$ ~ $\text{60}\text{40}$.