1-Silylvinyl ketones undergo smooth Michael addition with Grignardreagents generating magnesium enolates which are then trapped with benzaldehyde to give E- and Z-isomers of enones after Peterson condensation. (E)-Olefins become major products under a thermodynamic control when the condensation with benzaldehyde is carried out at room temperature in diethylether, while Z-isomers are more favored