Cascade cyclization of 1-(2-yl-3-phenylprop-2-enyl)-6-oxo-1,6-dihydropyridine-2-carbonitrile radical: Mechanistic insights from DFT study

Hybrid DFT calculations of mechanism of the titled reaction have been carried out by employing the BHandHLYP method combined with the 6-311++G(d,p), 6-311G(d,p), 3-21G, and LANL2DZ basis sets. The calculated results indicated that the radical precursor (Z)-1-(2-iodo-3-phenylprop-2-enyl)-6-oxo-1,6-dihydropyridine-2-carbonitrile prefers to undergo a deiodination to provide the titled free radical, followed by a tandem radical cyclization to construct several tetracyclic radical intermediates. The mechanism of the cascade radical cyclization was evaluated by the computed activation Gibbs free energies, intrinsic reaction barriers, attack angles, and orbital interaction energies. Further, we also explored the H-abstraction oxidations of the formed tetracyclic radicals by different abstractors. An excellent agreement with the available experiment was observed. The present investigation of reaction mechanism would be helpful not only for understanding the nature of radical chemistry but also for further experimental explorations.