Highly Stereoselective Gem-Dimethylcyclopropanation of Allylic Alcohols Promoted by Alkylidene Titanocenes

Abstract

A novel methodology for the direct gem-dimethylcyclopropanation of a series of acyclic and cyclic primary and secondary allylic alcohols is herein described. The reaction proceeds in a regio-, chemo-, and stereoselective manner, affording the corresponding gem-dimethylcyclopropane derivatives in moderate yields. We postulate that an alkylidene titanocene, generated in situ from sub-stoichiometric amounts of low-valent titanium species, Mg and 2,2-dichloropropane under mild reaction conditions, serves as the active species. The scope, limitations and a plausible mechanism of this metal-promoted transformation are also presented.