The first highly asymmetric Pummerer-type cyclization of chiral, non-racemic β-amidosulfoxides leading to enantiomerically enriched β-lactams (80–85 % ee) is described. S-and R-sulfoxides (S-2a-d and R-2a-c) were treated with O-methyl-O-tert-butyldimethylsilyl ketene acetal (1) in the presence of a catalytic amount of ZnCl 2 in CH 2 Cl 2 to predominantly give the corresponding 4R- and 4S-β-lactams (R-4a-d and S-4a-c) in more than 80 % ee. These results show that the stereoinduction is completely influenced by the absolute configuration of the sulfoxides.