N-Sulfonyl oxaziridines are susceptible to electrophilic activation using copper(II) catalysts and react with styrenes under these conditions to provide 1,3-oxazolidines in a formal aminohydroxylation of the alkene. We propose a two-step mechanism involving a cationic intermediate to account for the rate differences and regioselectivities observed using a variety of styrenes. In accord with our hypothesis, aminohydroxylations of a range of substrates bearing electron-stabilizing groups are successful, and 1,3-dienes are particularly good substrates for copper(II)-catalyzed aminohydroxylation. Reactions of unsymmetrical dienes provide good to excellent olefin selectivity, the sense and magnitude of which can be rationalized upon consideration of the stability of the cationic intermediates suggested by our mechanism. Diastereoselective synthesis of a diverse range of densely functionalized structures can be achieved by polyfunctionalization of dienes using aminohydroxylation as a key complexity-increasing step.