화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.142, No.11, 5408-5418, 2020
Duality of Reactivity of a Biradicaloid Compound with an o-Quinodimethane Scaffold
Sigmarene, which is a Kekule hydrocarbon with appreciable singlet biradical character originating from an o-quinodimethane scaffold, is isolated as a doubly sigma-bonded dimer. The dimer dissociates into a monomeric sigmarene upon heating or photoirradiation. The monomeric species undergoes a rapid [4 + 4] cycloaddition reaction under dark conditions even at room temperature to produce the dimer. Contrarily, the monomeric sigmarene undergoes a [4 + 2] cycloaddition reaction in the presence of dienophile as an orbital symmetry allowed process. Therefore, the sigmarene shows high reactivity for both symmetry-forbidden and allowed processes in the framework of the orbital symmetry rule. This duality of reactivity of the sigmarene is consistent with the intermediate singlet biradical character (44%) estimated by a density functional theory (DFT) calculation.