A method is described for producing vicinal diamines comprising the steps of converting a compound, possessing a leaving group on a carbon atom interposed between carbon atoms containing amino groups, to an aziridine-containing compound and reacting the latter compound with a nucleophile to form a vicinal diamine. The compound chosen for the rearrangement reaction may be selected from a wide range of compounds, including those with halide, heteroatom and aryl substituents. The amino groups may be blocked or unblocked. A variety of functional groups, including those which extend the carbon backbone, may be incorporated via opening of the aziridine-containing compound by addition of a selected nuclepohile. Aziridine-containing compositions and vicinal diamine compositions are disclosed. Functionalized vicinal diamines have numerous uses, including as intermediates for radionuclide-chelating ligands for use in the diagnosis and therapy of cancer.