Effect of Lewis acid catalysts on Diels-Alder and hetero-Diels-Alder cycloadditions sharing a common transition state
Effect of Lewis acid catalysts on Diels-Alder and hetero-Diels-Alder cycloadditions sharing a common transition state
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DOI：
10.1021/jo801076t
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发表时间：
2008-10-03
影响因子：
3.6
通讯作者：
Houk, K. N.
中科院分区：
文献类型：
--
作者：
Celebi-Oelcuem, Nihan;Ess, Daniel H.;Houk, K. N.
[图表]采用密度泛函理论（DFT）方法研究了β，γ-不饱和α-酮基膦酸酯和硝基烯烃与环戊二烯的热和刘易斯酸催化环加成反应。在这两种情况下，只有一个高度异步的双周环过渡态产生的狄尔斯-桤木和hetero-Diels-桤木环加合物可以定位。逐步途径被发现是更高的能量。在势能面上，双周环加成过渡态之后是Claisen相关过渡态。没有中间体位于这些过渡态之间。克莱森重排过渡态也是高度异步的，但与双周环过渡态相比，键长在相反的方向上偏斜。双周环和克莱森重排过渡态的相对位置可以控制周选择性，由于势能面的形状和相应的动力学影响。检查的热势能面（PES）表明，大多数的下坡路径后的双周环过渡态导致的Diels-桤木环加合物，而一个较小的数量的下坡路径到达杂Diels-桤木产品没有干预的能量障碍。刘易斯酸催化剂通过将环加成和克莱森重排过渡态向相反方向移动来改变表面的形状。这种地形变化定性地影响后的双周环过渡态的分支比，并最终逆转的环加成的周选择性，从而优先考虑杂狄尔斯-桤木环加合物。
[GRAPHICS]The thermal and Lewis acid catalyzed cycloadditions of beta,gamma-unsaturated alpha-ketophosphonates and nitroalkenes with cyclopentadiene have been explored by using density functional theory (DFT) methods. In both cases, only a single highly asynchronous bis-pericyclic transition state yielding both Diels-Alder and hetero-Diels-Alder cycloadducts could be located. Stepwise pathways were found to be higher in energy. On the potential energy surface, the bis-pericyclic cycloaddition transition state is followed by the Claisen rearrangernent transition state. No intermediates were located between these transition states. Claisen rearrangement transition states are also highly asynchronous, but bond lengths are skewed in the opposite direction compared to the bis-pericyclic transition states. The relative positions of the bis-pericyclic and Claisen rearrangement transition states may control periselectivity due to the shape of the potential energy surface and corresponding dynamical influences. Inspection of the thermal potential energy surface (PES) indicates that a majority of downhill paths after the bis-pericyclic transition state lead to the Diels-Alder cycloadducts, whereas a smaller number of downhill paths reach the hetero-Diels-Alder products with no intervening energy barrier. Lewis acid catalysts alter the shape of the surface by shifting the cycloaddition and the Claisen rearrangement transition states in opposite directions. This topographical change qualitatively affects the branching ratio after the bis-pericyclic transition state and ultimately reverses the periselectivity of the cycloaddition giving a preference for hetero-Diels-Alder cycloadducts.