Theoretical studies for ozonide formation during the ozonolysis of bicyclic endoperoxides

Abstract

Theoretical investigations on the treatment of bicyclic endoperoxides (1,2-dioxines) with ozone at the HF/6-31G*, MP2/6-31G*or 6-311G*, and DFT(B3LYP)/6-31G*levels of theory indicate that the estimated activation energies for formation of the possible endo-endo, endo-exo, exo-endo, or exo-exo transition states along with the formation of the primary ozonides and product ozonides are very sensitive to effects of electron correlation and basis set. This study suggests that MP2/6-311G*is the best level of theory for evaluating such systems. At the MP2/6-311G*level of theory it was found that the transition state for primary ozonide formation was lowest in energy when ozone approaches in an endo facial fashion with a further 3kJmol-1 stabilisation seen when the central oxygen within the primary ozonide protrudes outwards (exo) as opposed to inwards (endo). The product ozonides are predicted to be more stable than the combined starting materials by some 380-580kJmol-1 depending on the level of theory, clearly highlighting the substantive exothermic nature of this type of ozonolysis reaction.