New potentially bioactive α‐spiroaziridino‐γ‐ and ‐δ‐lactams have been prepared by treatment of α‐methylene‐γ‐ and ‐δ‐lactams with ethyl N‐{[(4‐nitrophenyl)sulfonyl]oxy}carbamate (NsONHCO2Et) in the presence of CaO. These compounds, through reductive aziridine ring opening, can be intermediates for the synthesis of α‐ and β‐aminolactams, which are useful as conformational constraints in peptides. The above procedure has been successfully extended to one α‐methyleneoxindole to obtain a new spirooxindole derivative, a potential precursor of natural alkaloids. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)