The photolysis of alkyl azoxy compounds RNN(0)R (11a, R = t-butyl; 11b, R = n-butyl) in pentane affords a new three-membered-ring heterocycle, an oxadiaziridine (12a, R = t-butyl; 12b, R = n-butyl). The oxadiaziridines revert to the azoxy compounds, t1/2 at 28° ≃ 5 hr. The isomerization is catalyzed by acids (fivefold acceleration for 12a by 1.7 M Cl2CHCOOH in CCl4) and shows a slight solvent effect (krel for 12a in CCl4, CH3OH, CH3NO2: 1, 2, 2.5). Compound 12a is reduced to the corresponding azo compound by acidified NaI in acetone; it is generally unreactive toward LiAlH4 or CH3Li. Compounds 11b and 12b are reduced to the corresponding azo compound by LiAlH4. Compound 12b is reduced by CH3Li to azobutane and butyraldehyde n-butyl-hydrazone; 11b reacts with CH3Li to afford 1-methylazobutane.