Book excerpt: A single synthetic method rarely is sufficient to provide universal access to a chemical structure class. This realization forces organic chemists to devise and develop new methods. The copper catalyzed ring expansion of vinylaziridines produces nitrogen containing heterocycles commonly found in pharmaceuticals and natural products. This reaction is described from its initial discovery, through optimization, to application. Many substitution patterns and functional groups were tested and the reaction was found to be quite tolerant. By controlling the aziridine and olefin stereochemistry the selective synthesis of either cis or trans 2,5dihydropyrroles was achieved. Likewise, vinyloxiranes were stereoselectively converted to cis- or trans-2,5-dihydrofurans. Furthermore, the asymmetric synthesis of 2-substituted-2,5-dihydrofurans was achieved using chirality transfer characteristic of a [1,3]- sigmatropic rearrangement. This method was further tested by completing the total synthesis of natural products goniothalesdiol and varitriol.