Optically pure alpha-(trimethylsilyl)benzyl alcohol: a practical chiral auxiliary for oxocarbenium ion reactions.

[reaction: see text] Enantiopure (S)-alpha-(trimethylsilyl)benzyl alcohol (98% ee) was prepared by Noyori's transfer hydrogenation of benzoyltrimethylsilane. The corresponding trimethylsilyl ether was subjected to Marko's silyl modified Sakurai conditions with a variety of aldehydes to afford homoallylic ethers in high diastereoselectivity. The practicality of the alpha-trimethylsilyl benzyl group as an oxocarbenium ion auxiliary was further demonstrated by its efficient deprotection or conversion to a benzyl protecting group.