Tri-tert-butoxyaluminum reacts with tert-butyl hydroperoxide to produce di-tert-butoxytert-butyl alumotrioxide, which decomposes heterolytically to form singlet dioxygen and homolytically with the O-O bond cleavage. The (BuOO.)-O-t, ((BuO)-O-t)(2)AlOO., (BuO.)-O-t, and ((BuO)-O-t)(2)AlO. radicals were identified by ESR using spin traps. These findings confirm the formation of aluminum-containing trioxide. The above radicals initiate alkylarene oxidation by the tri-tert-butoxyaluminum-tert-butyl hydroperoxide system. The carbon-centered and alkylperoxy radicals originated from the oxidized substrates were identified.