Cyclization of N-(propargylic)hydroxylamines catalyzed by AgBF4 afforded the corresponding 4-isoxazolines in good yields. Copper salts were found to promote the further transformation to acylaziridines. The combined use of AgBF4 and CuCl realized direct transformation of N-(propargylic)hydroxylamines into cis-acylaziridines.