Upon heating of a mixture of N,N-disubstituted aromatic selenoamides and several electron-deficient olefins in the presence of copper(0) powder, a novel deselenative cyclopropanation takes place to afford the corresponding aminocyclopropanes in good yields. When acrylonitrile is employed as an electron-deficient olefin, the aminocyclopentanation occurs in preference to the aminocyclopropanation by