18O-Tracer Studies of Fe(II)-Induced Decomposition of 1,2,4-Trioxolanes (Ozonides) Derived from Cyclopentenes and Indenes. Inner-Sphere Electron Transfer Reduction of the Peroxide Linkage

Fe(II)-induced decomposition of 1,2,4-trioxolanes (ozonides) 1 and 2 is studied in detail. The inner-sphere electron transfer reduction, which is sensitive to steric effects, is proposed to be a reasonable mechanism for the peroxide decomposition, i.e., the selective generation of one of the two possible Fe(III)-complexed oxy radicals. The fate of the oxy radical species is revealed in detail by using 18O-tracer studies in the reduction of 18O-labeled ozonides 1a and 2a, in which the ethereal oxygens are labeled by 18O atom (18O, 77%) and also by the reduction in the presence of H218O (18O, 10%). The results of the 18O-tracer studies are consistent with the regioselective generation of the Fe(III)-complexed oxy radical species.