Stereoselective preparation of 2-silylated 1,3-diols and the regioselectivity of their Peterson olefination

The reduction of the carbonyl group of alpha-silylated aldols with complex hydrides was shown to proceed with high stereoselectivity. The center of chirality in the alpha-position to the ketone, at the C-atom where the silicon group is attached, usually dominated the stereochemical control of the reaction. The presence of the beta-hydroxy functionality, however, also seems to be necessary for a high degree of selectivity. Peterson olefination of 2-silylated 1,3-diols afforded stereoselectively (E)-configured allylic alcohols as the major products. With KH as the base, the reaction proceeds predominantly in a syn-fashion, preferring to eliminate a syn- rather than an anti-configured beta-hydroxysilane unit. Under 'silico-nucleophilic' conditions (OH- or F-), an anti-configured beta-hydroxysilane moiety can also be eliminated in an anti-fashion. This reaction is strongly preferred over the corresponding syn-elimination, but is still less prominent than a competitive syn-elimination of a syn-configured beta-hydroxysilane unit. (C) 1999 Elsevier Science Ltd. All rights reserved.