Origin of the Preferential Formation of Helicenes in Mallory Photocyclizations. Temperature as a Tool to Influence Reaction Regiochemistry
Origin of the Preferential Formation of Helicenes in Mallory Photocyclizations. Temperature as a Tool to Influence Reaction Regiochemistry
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马洛里光环化中螺旋烯优先形成的起源。
DOI：
10.1021/acs.joc.8b02671
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Clennan, E. L.
中科院分区：
文献类型：
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作者：
Weber, J.;Clennan, E. L.
从实验和计算的角度研究了四种bis-Mallory光环化底物的区域化学。所有三种可能的区域异构体的形成仅在其中一种底物的反应中观察到。在其他三种底物中，只有两种C2对称产物生成，而没有C1产物生成。在仅形成两种产物的三个反应中，可以使用光环化温度来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也在形成三种产物的底物的光环化中起作用。然而，没有温度被定位为排他性的第三个组件，theC 2-对称的产品之一，总是形成旁边的一个或两个其区域异构体。采用B3 LYP/6-311+G（2d，p）方法计算了所有二氢菲（DHP）、四氢菲（THP）和单Mallory光环化反应中间体的能量。螺旋烯产物的DHP前体的振子强度比竞争性形成的DHP的振子强度小4.8-9.2倍。这一观察结果表明，光稳态的建立是螺旋烯优先形成的原因，螺旋烯已被观察到作为许多马洛里光环化的独特和有用的特征。
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 twoC2-symmetric products, but not theC1product, 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 theC2-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.