A NEW SELECTIVE ALLYL TRANSFER REAGENT - FACILE ENTRY TO BETA-HYDROXYENOL SILYL ETHERS BEARING 2 CONTIGUOUS STEREOGENIC CENTERS

eta(3)-Allyltitanium(III) complexes functionalized on the C-2 with a s ilyloxy 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 dia stereoselective addition with aldehydes to produce, depending on the t reatment applied, anti diastereomeric beta-hydroxy silyl enol ethers o r beta-hydroxy ketones. Two defined contiguous stereocenters make the enol silyl ethers containing them versatile synthons for further stere ocontrolled transformations. The reaction constitutes a new method for directing electrophiles to the alpha-position of the alpha,beta-enone system.