Chiral Allylsilane Additions to Chiral alpha-Substituted Aldehydes

chiral allylsilane 3 reacted with chiral a-methyl-b-siloxy-aldehydes to afford the corresponding 1,4-syn-products with good diastereoselectivities independent of the absolute stereochemistry of these aldehydes. the best selectivities are observed when the reactions are carried out by transmetallation of the allylsilane 3 using tin (iv) chloride in ch2cl2, at -78 °c, before addition of the aldehydes.