The preparation of aziridine-2,2-dicarboxylates via 1,4-addition of N,O-bis(trimethylsilyl)hydroxylamine to α,β-unsaturated malonates in the presence of chiral Lewis acids is reported. Good enantioselectivity was observed for conjugate addition catalysed by [Cu(S,S)-Bn-(box)](OTf)2 on isobutylidene and 3-methylbutylidene malonate.