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Origin of the Preferential Formation of Helicenes in Mallory Photocyclizations. Temperature as a Tool to Influence Reaction Regiochemistry
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2018-12-12 00:00:00 , DOI: 10.1021/acs.joc.8b02671 J. Weber 1 , E. L. Clennan 1
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2018-12-12 00:00:00 , DOI: 10.1021/acs.joc.8b02671 J. Weber 1 , E. L. Clennan 1
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The regiochemistry of four bis-Mallory photocyclization substrates has been examined from experimental and computational perspectives. Formation of all three possible regioisomers was only observed in the reaction of one of the substrates. In the other three substrates, only the two C2-symmetric products, but not the C1 product, were formed. In the three reactions that only formed two products, the photocyclization temperature could be used to select for exclusive formation of one or the other regioisomer. The use of temperature to select between two regioisomers also worked in the photocyclization of the substrate that formed three products. However, no temperature was located for exclusive formation of the third component, one of the C2-symmetric products, which always formed alongside either one or both of its regioisomers. B3LYP/6-311+G(2d,p) calculations were used to determine the energies of all of the dihydrophenanthrene (DHP), tetrahydrophenanthrene (THP), and mono-Mallory photocyclization intermediates. The oscillator strengths of the DHP precursors to the helicene products were a factor of 4.8–9.2 smaller than those of competitively formed DHPs. This observation suggests that establishment of a photostationary state is responsible for the preferential formation of helicenes that has been observed as a unique and useful feature of many Mallory photocyclizations.
中文翻译：
马洛里光环化中螺旋藻优先形成的起源。温度是影响反应区域化学的工具
从实验和计算的角度检查了四个双马洛里光环化底物的区域化学。仅在底物之一的反应中观察到所有三种可能的区域异构体的形成。在其他三个基板中，仅形成两个C 2对称产物，但未形成C 1产物。在仅形成两种产物的三个反应中，光环化温度可用于选择一种或另一种区域异构体的排他性形成。使用温度在两种区域异构体之间进行选择还有助于形成三种产物的底物的光环化。然而，没有温度位于用于只形成所述第三组分，所述的一个Ç2-对称产物，通常与它的一个或两个区域异构体一起形成。使用B3LYP / 6-311 + G（2d，p）计算来确定所有二氢菲（DHP），四氢菲（THP）和单层光环化中间体的能量。DHP前体对Helene产品的振子强度比竞争形成的DHP小4.8-9.2倍。该观察结果表明，建立光平稳状态是螺旋藻优先形成的原因，已观察到其是许多马洛里光环化的独特且有用的特征。
更新日期：2018-12-12
中文翻译：
马洛里光环化中螺旋藻优先形成的起源。温度是影响反应区域化学的工具
从实验和计算的角度检查了四个双马洛里光环化底物的区域化学。仅在底物之一的反应中观察到所有三种可能的区域异构体的形成。在其他三个基板中，仅形成两个C 2对称产物，但未形成C 1产物。在仅形成两种产物的三个反应中，光环化温度可用于选择一种或另一种区域异构体的排他性形成。使用温度在两种区域异构体之间进行选择还有助于形成三种产物的底物的光环化。然而，没有温度位于用于只形成所述第三组分，所述的一个Ç2-对称产物，通常与它的一个或两个区域异构体一起形成。使用B3LYP / 6-311 + G（2d，p）计算来确定所有二氢菲（DHP），四氢菲（THP）和单层光环化中间体的能量。DHP前体对Helene产品的振子强度比竞争形成的DHP小4.8-9.2倍。该观察结果表明，建立光平稳状态是螺旋藻优先形成的原因，已观察到其是许多马洛里光环化的独特且有用的特征。
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