Tetrachlorocyclopentadienylidene, generated by the photolysis of tetrachlorodiazocyclopentadiene, has been shown to undergo carbon-hydrogen insertion in cyclohexane, carbon-chlorine insertion in carbon tetrachloride, and to add to olefins to give cyclopropyl compounds. The addition to cis-2-butene was nonstereospecific. The reaction with 2-methyl-2-butene gave 1, 2, 3, 4-tetrachloro-6, 6, 7-trimethylspiro [2.4] hepta-1, 3- ...