Multi-component orbital interactions during oxyacyl radical addition reactions involving imines and electron-rich olefins

Abstract

Ab initio and DFT calculations reveal that oxyacyl radicals add to imines and electron-rich olefins through simultaneous SOMO–π*, SOMO–π and π*–HOMO interactions between the radical and the radicalophile. At the BHandHLYP/aug-cc-pVDZ level, energy barriers of 20.3 and 22.0 kJ mol⁻¹ are calculated for the attack of methoxycarbonyl radical at the carbon and nitrogen ends of methanimine, respectively. In comparison, barriers of 22.0 and 8.6 kJ mol⁻¹ are calculated at BHandHLYP/aug-cc-pVDZ for reaction of methoxycarbonyl radical at the 1- and 2-positions in aminoethylene, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO–π*, SOMO–π and π*–LP interactions are worth 111, 394 and 55 kJ mol⁻¹ respectively in the transition state (8) for reaction of oxyacyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.