Cyclopropyl- and Allyl-substituted Arenes in Reaction with Dinitrogen Tetroxide. Effect of Substrate Oxidation Potential on Reaction Direction

A correlation was found between oxidation potentials of acylcyclopropanes in solution (in CH₂Cl₂ and CH₃CN) and their HOMO energies calculated by semiempirical (AM1) and nonempirical (HF/6-31G and HF/6-31G**) methods. The correlation provides a possibility to forecast the reaction direction of the mentioned substrates and N₂O₄. The correlation possesses a general character. It was established for instance that arylcyclo-propanes, cyclopropylmethyl- and allylbenzenes oxidized at more positive potentials than reduction potential of NO⁺ and having more positive e_HOMOthan 9.0 eV (AM1), 8.4 eV (HF/6-31G), and 8.3 eV (HF/6-31 G**) reacted with N₂O₄ following the mechanism "electron transfer radical pair recombination" affording nitroaromatic derivatives retaining the cyclopropane (or allyl) fragments. Substrates of the same type where the electron transfer to NO⁺ should be endothermic process and whose HOMO values are less than the above critical numbers react with N₂O₄ by the mechanism of electrophilic cyclopropane ring opening (with aryl and benzylcyclopropanes) or by electrophilic addition across the double C=C bond (with allylbenzenes).