Diastereoselective additionreaction of ester enolates to a chiral imine possessing (4S, 5S)-4,5-dimethoxymethyl-2-methyl-1,3-dioxolane ring as a chiral auxiliary is reported, in which varying metal enolates resulted in the selective formation of (4S)- or (4R)-β-lactam. Namely, addition of the lithiumenolates provided (4S)-β-lactams, whereas the triisopropoxytitanium enolates effected selective formation