A method is described which provides for the direct asymmetric catalytic synthesis of trisubstituted aziridines from imines and diazo compounds. While unactivated imines were not reactive to alpha-diazo carbonyl compounds in which the diazo carbon was disubstituted, N-Boc imines react with both alpha-diazo esters and alpha-diazo-N-acyloxazolidinones to give trisubstituted aziridines with excellent diastereo- and enantioselectivities.