Ring expansion of aziridine-2-carboxylates. An efficient entry to imidazolidin-2-ones and oxazolidin-2-imines

N-Alkylaziridine-2-carboxylates undergo ring expansion into imidazolidin-2-ones upon reaction with N-alkyl isocyanates in the absence of a catalyst. On the other hand, when the N-alkyl group of the isocyanate was replaced with an N-phenyl group, oxazolidin-2-imines were formed. The scope of both processes is demonstrated through the use of different substituted aziridine-2-carboxylates.