Peterson olefination from α-silyl aldehydes

A procedure for the stereoselective synthesis of substituted alkenes from alpha-silyl aldehydes, via the Peterson reaction, is described. The protocol for the preparation of alpha-silyl aldehydes is also included. Organometallic addition to the alpha-silyl aldehyde gives erythro-beta-hydroxysilanes in high yields (85-90%), which undergo elimination on treatment with potassium hydride (KH) or boron trifluoride to afford respectively Z-o E-alkenes (87-90%). The method described has been carried out using alpha-silyl aldehydes bearing the tert-butyldiphenylsilyl group. This bulky group increases the stability of the silyl aldehyde, enhances the stereoselectivity of the formation of the beta-hydroxysilanes and favors the stereocontrol of the elimination step, thus providing high yields of stereo-defined alkenes. Here we describe a two-step protocol for the synthesis of Z-1-phenyl-1-hexene from 2-tert-butyldiphenylsilyl-2-phenylethanal and n-butyllithium, followed by elimination of the resulting (1S*, 2R*)-1-tert-butyldiphenylsilyl-1-phenylhexan-2-ol with KH. The total time for the synthesis, purification and isolation of the alkene is 2 days.