Applications of Aziridinium Ions. Selective Syntheses of β-Aryl-α,β-diamino Esters ChuangTsung-Hsun SharplessK. Barry 1999 α<b>,</b>β<b>-</b>Diamino esters are readily prepared through stereospecific and regioselective opening of an aziridinium ion intermediate with a variety of amines. The aziridinium ion is generated from the epoxide in two steps.