THE CHEMISTRY OF CHLOROSILYL ENOLATES .3. VARIATION OF THE SILYL GROUP AND THE EFFECT ON RATE AND ENANTIOMERIC EXCESS OF ACETATE ALDOL ADDITIONS

The rates of reaction of the silyl ketene acetals CH2=C(OMe)OSiCl2R (1 a-d) with benzaldehyde and pivalaldehyde have been determined and foll ow the order R = H similar to Cl > Ph > Me. These reactions are promot ed by catalytic amounts of a chiral phosphoramide; enantioselectivitie s of the products obtained show a high sensitivity towards variation o f the silyl group. The reactions of the dialkyl substituted chlorosily l enolates CH2=C(OMe)OSiClR2 (1e,f) with benzaldehyde are not promoted by HMPA.