3-oxazolidines 1 with m-chloroperbenzoic aicd was reinvestigated. Aminoxyls 5 are isolated in good yields in ether at −15 °C, or in anhydrousdichloromethane at 0 °C. Oxaziridines 4 are promoted at room temperature, or in the presence of an acid. In any case, short reaction times prevented the degradation of aminoxyls and oxaziridines. The competition between oxaziridines 4 and aminoxyls 5 is ruled by