Treatment of the bromohydroperoxides of 2-methyl-2-butene and ethylidenecyclohexane with cold methanolic base produces trimethyl- and 4-methyl-3,3-pentamethylene-1,2-dioxetane, 3 and 8. Under these conditions the bromo- and iodohydroperoxides of 2,3-dimethyl-2-butene A, 1,2-dimethylcyclohexene B, and Δ9,10-octalin C are converted rapidly to the corresponding allylic hydroperoxides. The reaction in methylene chloride between silver ion and the bromo-and iodohydroperoxides of A and the iodohydroperoxides of B and C produces the corresponding dioxetanes in 20–30% yield: tetramethyl-1,2-dioxetane 11, 3,4-dimethyl-3,4-butano-1,2-dioxetane 15, and 3,4:3,4-dibutano-1,2-dioxetane 23. About 50% of the corresponding allylic hydroperoxides also are formed as are pinacolone, ∼15%, 1-acetyl-1-methylcyclopentane, ∼20%, and Δ9,10-octalin, ∼1%, from the appropriate halohydroperoxides.All the dioxetanes are yellow, thermolyze to give only carbonyl cleavage products, and are luminescent. Reduction of 3 with bisulfite ion produced trimethyloxacyclopropane and with iodide ion 2-methyl-2,3-butanediol. Reduction of 8, 11, 15, and 23 with lithium aluminum hydride at −78° gave good yields of the corresponding diols. Treatment with triphenylphosphine of 11 gave tetramethyloxacyclopropane, of 15, a 1:3 ratio of 2-methylene-1-methylcyclohexanol and 2,3-dimethylcyclohexen-3-ol, and of 23, 10-hydroxy- Δ1,9-octalin.Activation parameters for thermolysis of the dioxetanes are (dioxetane, Ea, kcal/mol, ΔS+, e.u.) 3, 23.5 ± 0.5, −5 ± 2; 11, 25.8 ± 0.5, −2 ± 2; 15, 25.7 ± 0.7, 2 ± 2; 23, 22.7 ± 0.9, −3 ± 3.