Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8571, Japan.
J Phys Chem A. 2012 Feb 2;116(4):1168-75. doi: 10.1021/jp211542m. Epub 2012 Jan 23.
We report ab initio molecular dynamics calculations based on density functional theory performed on an intramolecular [2 + 2] cycloaddition between ketene and olefin linked with a 2,4-pentanediol (PD) tether. We find that the encounter of the ketene and olefin moieties could be prearranged in the thermal equilibrated state before the cycloaddition. The reaction mechanism is found to be stepwise, similar to that of intermolecular ketene [2 + 2] cycloadditions with ordinary alkenes. A distinct feature of the reaction pathway for a major diastereoisomer is a differential activation free energy of about 1.5 kcal/mol, including 2.8 kcal/mol as the differential activation entropy, with a transition state consisting of a flexible nine-membered ring in the olefin-PD-ketene moiety. This theoretical study provides a reasonable explanation for the strict stereocontrollability of the PD-tethered ketene-olefin cycloaddition, irrespective of reaction types or conditions.
我们报告了基于密度泛函理论的从头分子动力学计算，该计算针对的是通过 2,4-戊二醇（PD）连接链连接的酮烯内[2+2]环加成反应。我们发现，在环加成之前，酮烯部分的相遇可以在热平衡状态下预先排列。反应机理被发现是分步的，类似于普通烯烃的分子间酮烯[2+2]环加成。主要非对映异构体反应途径的一个显著特征是活化自由能的差异约为 1.5 千卡/摩尔，其中包括 2.8 千卡/摩尔的差异活化熵，过渡态由烯烃-PD-酮烯部分中的柔性九元环组成。这项理论研究为 PD 键合的酮烯环加成的严格立体控制提供了合理的解释，无论反应类型或条件如何。
