Chemo- and stereoselective palladium-catalyzed allylic alkylations controlled by silicon

A series of 2-silylbut-2-ene-1,4-diol derivatives 2 bearing different substituents on the silicon atom have been prepared and tested in palladium-catalyzed alkylations with dimethyl malonate. Totally chemo- and stereoselective, these high yielding reactions are strongly influenced by the presence of the silicon group on the allyl moiety. The preparation and reactivity of two analogues 9 where the silyl group is replaced by a tert-butyl group were also examined. Their difference of reactivity toward the nucleophile can be ascribed to the ability of the silicon group to stabilize a beta-carbocation. Indeed, both steric and electronic factors are responsible for this behavior.