The Power of Transition Metals: An Unen-

Vinyl aziridines are versatile starting materials toward ringexpansion transformations. Such processes are widely used to give various medium or larger N-heterocycles of synthetic interest. This letter describes a copper-catalyzed ring expansion of vinyl aziridines to 3-pyrrolines by using a Cu(I) salt [(CuOTf)2·toluene or Cu(MeCN)4·PF6]. In particular, this transformation occurs under mild conditions (THF, rt).