Laconsay Croix J, Jain Ishika, Schleif Tim, Karney William L, Wu Judy I
Department of Chemistry, University of Houston Houston Texas 77204 USA
Department of Chemistry, University of San Francisco San Francisco California 94117 USA
Chem Sci. 2025 Aug 26. doi: 10.1039/d5sc02914g.
Quantum mechanical tunnelling significantly influences the reactivity of strained ring systems, yet strategies for controlling such reactivity remain largely unexplored. Here, we identify geminal hyperconjugation, , electron delocalization between σ-bonds attached to a common atom, as a decisive electronic factor in governing heavy-atom tunnelling reactions involving three-membered rings. We illustrate this through a case study of the oxepin (1') ⇌ benzene oxide (1) equilibrium, recently shown to undergo solvent-controlled tunnelling at 3 K (, 2020, , 20318). Natural bond orbital analyses reveal that coordination of ICF, HO, or H to the oxygen atom of 1 enhances geminal C-O σ → O-C σ* delocalization in the oxirane ring, strengthening the C(1)-C(6) bond, and facilitating the 1' to 1 rearrangement. Tunnelling-inclusive Arrhenius plots show increasingly large deviations from a linear relationship for the electrocyclizations of 1' → 1, 1'-2HO → 1-2HO, and 1'-H → 1-H. Related cases, including benzene sulfide (1S), oxirane (2), and benzazirine (3), are examined.
量子力学隧穿对张力环体系的反应活性有显著影响，但控制这种反应活性的策略在很大程度上仍未得到探索。在这里，我们确定偕位超共轭，即连接到共同原子的σ键之间的电子离域，是控制涉及三元环的重原子隧穿反应的决定性电子因素。我们通过氧杂环庚三烯（1'）⇌氧化苯（1）平衡的案例研究来说明这一点，最近发现该平衡在3 K下会发生溶剂控制的隧穿（，2020，，20318）。自然键轨道分析表明，ICF、HO或H与1的氧原子配位会增强环氧乙烷环中偕位C-O σ→O-C σ*离域，加强C(1)-C(6)键，并促进1'到1的重排。包含隧穿的阿伦尼乌斯图显示，对于1'→1、1'-2HO→1-2HO和1'-H→1-H的电环化反应，与线性关系的偏差越来越大。我们还研究了相关的案例，包括苯硫醚（1S）、环氧乙烷（2）和苯并氮杂环丙烯（3）。
