Cheol-Min Yook, Heesung Eum, Hyun-Joon Ha,* Kyung Yeon Kang,‡ and Won Koo Lee‡,*

The synthetic utility of nitrogen containing three-membered ring, aziridine1, stems from the ring-opening reaction toward acyclic α- or β-amines or ring expanded heterocycles.2 The regioselectivity of this reaction is one of the most essential elements of their synthetic values. The origin of ring openings or ring expansion reactions of aziridines is the ring strain which is quite similar to cyclopropane and oxirane when the ring nitrogen has hydrogen.1 However, the characteristics and the ring strain of aziridine depend on the substituents at the aziridine-ring nitrogen.3 The aziridine ring bearing electron withdrawing substituent, so called activated aziridine, is quite labile to the incoming nucleophiles. Unactivated aziridine is stabilized by the electron-donating substituent at the ring nitrogen with the resistance to the reaction with nucleophiles for the ring-opening reactions. Thereby, proper activation is needed to carry out the reaction of unactivated aziridines, and often made through chelation with Lewis acid or bond formation with acyl, trimethylsilyl, protonyl or alkyl group toward aziridinium ion.