Racemic 3-cyclohexyl-1-methyldiaziridine was found to react with alpha,beta -unsaturated amides in basic conditions, giving N-unprotected trans-aziridines, while 3,3-pentamethylenediaziridine had been reported to afford cis-aziridines in high diastereoselectivity. The trans-selectivity was partially dependent on the stereochemistry of the substrate. The stereochemistries of these reactions were reasonably explained by the conformational analysis of the intermediary enolates.