Polyheterocyclic scaffolds were prepared by intramolecular aza-[4+3] cycloaddition reactions of aza-oxyallylic cations with cyclic dienes. The aza-oxyallylic cation was generated in situ by the dehydrohalogenation of α-halohydroxamates. The highly functionalized heterocyclic products undergo a variety of reactions that provide useful scaffolds for target-directed synthesis, including macrocyclic furans and polyhydroxylated azepanes.