Reaction of N-arylsulfonyl allylamines with alkyl nitriles in the presence of di-tert-butyl peroxide (DTBP) and a catalytic amount of copper salt afforded homologated aziridines in 43-86% yield. A sequence involving addition of the in situ generated cyanomethyl radical to the double bond followed by a copper-mediated intramolecular C-N bond formation accounted for the reaction outcome. 2,3-Disubstituted allylamines were converted to trisubstituted aziridines in a stereoselective manner. Starting from enantioenriched allylamines, chiral aziridines were obtained diastereoselectively.