Li+ and Na+ switch of enantioselectivity in the desymmetrisation of polycyclic bis(phenylsulfonyl)alkenes by chiral alcohols

A complete switch of enantioselectivity is obtained in the desymmetrisation reaction of polycyclic bis(phenylsulfonyl)alkenes by the change of the base from n-BuLi to NaH, thus allowing convenient access to either enantiomer of polycyclic ketones with the same chiral auxiliary.