We report herein an efficient Cu-catalyzed formal [3 + 3] cycloaddition of isocyanoacetates with readily available aziridines of different substitution patterns, which provides a practical access to valuable 1,4,5,6-tetrahydropyrimidine derivatives. In particular, the use of enantiopure aziridines delivers disubstituted tetrahydropyrimidines bearing a 1,3-diamino unit in good yields as a single stereoisomer (>20:1 dr, > 99% ee). The heterocyclic products can also be easily converted to synthetically useful amino alcohol derivatives or α,γ-diamino acids.