We report here a one-step synthesis of the 4,5,6,7-tetrahydro-lH-1,2,4-triazolo[4,3-dI1,4]diazepine, 4-6, and 1,2,4-oxadiazolo[4,5-dIl,4]-diazepine, 7-10, by 1,3-dipolar cycloaddition of nitrile imines and nitrile oxides with 2,3-dihydro-1H-1,4-diazepine, 1. In all cases these cycloadditions are peri- and regioselectives (the C = N bond is sole affected) and occurs with high yields. Structure and conformations of cycloadducts have been assigned by means of nmr analysis.