© 1995 Georg Thieme Verlag. All rights reserved. The regioselective copper catalysed aziridination of 1,3-dienes using PhI=NTs is reported. For unsymmetrical dienes, the major product is that resulting from reaction of the more electron rich double bond. When the two double bonds are electronically similar, steric hindrance governs the selectivity. In some cases rearrangement of the vinyl aziridine to the corresponding 3-pyrroline was observed. The reaction of 1,3-cyclooctadiene gave the 3-pyrroline (5) exclusively.