Pei Zhipeng, Connor Kieran P E, Magann Nicholas L, Gardiner Michael G, Coote Michelle L, Sherburn Michael S
Institute for Nanoscale Science & Technology, Flinders University, Bedford Park, South Australia 5042, Australia.
Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia.
Org Lett. 2024 Sep 27;26(38):8110-8114. doi: 10.1021/acs.orglett.4c03001. Epub 2024 Sep 16.
The latent singlet diradical character of the parent -quinonedimethide (-QDM), as revealed by valence bond calculations, is demonstrated experimentally by trapping with the kinetically stable free radical TEMPO at room temperature. In the absence of TEMPO, the main pathway for decomposition at ambient temperature is not (as previously proposed in the literature) a radical reaction but instead a concerted Diels-Alder dimerization, which through ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD calculations is shown to proceed through an ambimodal bispericyclic transition state. The predominantly non-radical reactivity of -QDM at room temperature differs from that of its isomeric -quinonedimethide (-QDM) congener, which self-reacts through radical pathways. These findings suggest the potential for tunable concerted/stepwise cycloadditions.
价键计算表明，母体醌二甲烷（-QDM）具有潜在的单线态双自由基特征，通过在室温下用动力学稳定的自由基TEMPO捕获进行了实验证明。在没有TEMPO的情况下，室温下分解的主要途径不是（如文献中先前提出的）自由基反应，而是协同的狄尔斯-阿尔德二聚反应，通过ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD计算表明，该反应通过双模态双周环过渡态进行。-QDM在室温下主要的非自由基反应性与其异构体醌二甲烷（-QDM）同系物不同，后者通过自由基途径进行自反应。这些发现表明了可调谐协同/逐步环加成反应的潜力。
