3-Disubstituted N-phosphorylated aziridines except N-phosphorylated cyclohexenimine (4) do not react under the described conditions. Copper-mediated reaction of 2-phenyl-N-(diethoxyphosphoryl)aziridine (7) with Grignard reagents affords a mixture of regioisomers (8) and (9) but still with the preference of ring-opening at the carbon of lesser substitution.