Synthesis of enantiopure homoallylic ethers by reagent controlled facial selective allylation of chiral ketones

The stereoselective allylation of chiral methyl ketones to give tertiary ho moallylic ethers, which can easily be transformed into homoallylic alcohols , is described. Reaction of the enantiopure ketones 8 a-d and the racemic k etones 26a- d with the norpseudoephedrine derivative 2 or ent-2 and allylsi lane in the presence of a catalytic amount of trifluoromethanesulfonic acid , led to a series of homoallylic ethers with good to excellent diastereosel ectivity (85:15 to > 97:3). The allylation is reagent controlled and nearly independent from the stereogenic centers in the substrates. A partial kine tic resolution was observed using the racemic ketones 26a-d. In the reactio n of the chiral ketones 8a-d with the achiral reagents ethoxytrimethylsilan e and allylsilane only a low diastereoselectivity was observed.