Synthesis of enantiopure homoallylic alcohols by a highly selective asymmetric allylation of ketones

A highly selective asymmetric domino allylation of aliphatic ketones is described. When methyl ketones 1a-g, the chiral trimethylsilyl ether 2, and allylsilane 3 react in the presence of catalytic amounts of trifluoromethanesulfonic acid, the homoallylic ethers 4a-g are produced with up to 24:1 diastereoselectivity and 89% yield. Cleavage of the obtained tertiary homoallylic ethers C using lithium or sodium in liquid ammonia gives the homoallytic alcohols 5 in 75 to 95% yield and up to 92% ee. Even ethyl methyl ketone 1a, the most difficult example, showed a stereoselectivity of 9:1 at -78 degrees C and 24:1 at -109 degrees C. In addition, the allylation of protected hydroxyalkyl methyl ketones 7a-j was investigated to give the corresponding homoallylic ethers 8a-j with a diastereoselectivity of up to >24:1 and 98% yield. In contrast, ethyl alkyl ketones 1h-j have a low selectivity.