Nitrile sulfides and nitrile oxides underwent periselective 1, 3-dipolar addition to the nitrile functions of tetracyanoethylene to form mono and bis thiadiazole and oxadiazole derivatives, respectively. Solvolysis reactions of the thiadiazoles and oxadiazoles were investigated. Diphenyldiazomethane added selectively to the carbon-carbon double bond of tetracyanoethylene to form l, l-diphenyl-2, 2, 3, 3-tetracyanocyclopropane in high yield.