A New Selective Allyl Transfer Reagent: Facile Entry to β-Hydroxy Enol Silyl Ethers Bearing Two Contiguous Stereogenic Centers

All articles of this category η 3 -Allyltitanium(III) complexes functionalized on the C-2 with a silyloxy group can be prepared by the reaction of titanocene dichloride with isopropylmagnesium chloride in the presence of the corresponding 2-silyloxybutadienes. These complexes undergo a highly regio- and diastereoselective addition with aldehydes to produce, depending on the treatment applied, anti diastereomeric β -hydroxy silyl enol ethers or β -hydroxy ketones. Two defined contiguous stereocenters make the enol silyl ethers containing them versatile synthons for further stereocontrolled transformations. The reaction constitutes a new method for directing electrophiles to the α -position of the α , β -enone system. allylation - η 3 -allyltitanium(III) complex - homoallylic alcohols - silyl enol ethers - stereocontrol