A Preferred Disrotatory 4n Electron Mobius Aromatic Transition State for a Thermal Electrocyclic Reaction
A Preferred Disrotatory 4n Electron Mobius Aromatic Transition State for a Thermal Electrocyclic Reaction
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DOI：
10.1002/anie.200806009
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发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Tsogoeva, Svetlana B.
中科院分区：
文献类型：
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作者：
Mauksch, Michael;Tsogoeva, Svetlana B.
Möbius芳香性，由Heilbronner在1964年预测，直到大约10年前才意外地被计算发现，[2]仍然吸引着许多化学家Zimmerman将这一概念推广到不具有Möbius-strip拓扑结构的结构，并在Dewar-Zimmerman对Woodward-Hoffmann规则的轨道对称控制反应的解释中成功地将这一思想应用于对周环反应的过渡态进行分类。[4,5]根据这一规律，热激活的电环反应通过4n电子“Möbius”芳香过渡态进行控制，通过4n+ 2电子“h<e:1> ckel”芳香过渡态结构进行扭曲，而光化学反应则表现出相反的行为。这些概念具有重要的合成应用，甚至可能在生物合成中发挥作用例如Nicolaou等人利用6和8个π电子电环反应进行了仿双花酸的全合成电环酶甚至被提出在体内支持6个π-电子电环反应1993年，Jiao和Schleyer首次报道了1,3,5 -庚三烯[1,7]-氢转移的“Möbius”芳香族过渡态的计算研究，该反应被认为发生在钙化醇重排到预钙化醇的过程中四年后，Johnson和Daoust提出Möbius苯是由杜瓦苯中“禁止的”控制环打开模式产生的他们意识到这种反应模式不符合Woodward-Hoffmann规则的预测。然而，在最近的一项研究中，据报道，虽然控制模式确实是首选的，Möbius苯不参与开环模式丁二烯-环丁烯转化的“禁止”旋转过渡结构被发现是一个二级鞍点[1,7]-氢位移中的高能“禁止”跃迁结构也有报道2005年，Rzepa为a (Z， E， Z)-decapentaene[15]的开环/闭环反应提出了一种Möbius扭曲和h<s:1> ckel芳香4n+ 2电子电环过渡态结构相比之下，Möbius芳香族过渡态的电环反应，并具有Möbius条形拓扑迄今尚未报道。在这里，我们报告了这种新型的周环反应过渡态结构的第一个代表。此外，提出了Möbius扭曲十二己烯的热环开环通过芳香过渡态，而不是通过Woodward-Hoffmann规则预测的具有h<s:1> ckel拓扑的环的控制过渡结构，优选地进行畸变，并且在理论的耦合团簇水平上，这在能量上是19.9 kcal molÀ1不利的！[16]
Möbius Aromaticity, predicted by Heilbronner in 1964,[1] and computationally discovered unexpectedly only about a decade ago,[2] continues to fascinate many chemists.[3] Zimmerman generalized the concept to include structures that do not possess the Möbius-strip topology and successfully applied the idea to categorize transition states of pericyclic reactions in the Dewar–Zimmerman interpretation of the Woodward–Hoffmann rules for orbital-symmetry controlled reactions.[4, 5] According to this rule, thermally activated electrocyclic reactions proceed conrotatory via a 4n electron “Möbius” aromatic transition state, and disrotatory via a 4n+ 2 electron “Hückel” aromatic transition state structure, while photochemical reactions show an opposite behavior. These concepts have important synthetic applications and might even play a role in biosynthesis.[6] Nicolaou et al., for example, used six and eight π-electron electrocyclic reactions in the biomimetic total synthesis of endiandric acids.[7] Electrocyclase enzymes are even proposed to support six π-electron electrocyclic reactions in vivo.[8] In 1993, Jiao and Schleyer reported a first computational study on a “Möbius” aromatic transition state for the [1, 7]-hydrogen shift in 1, 3, 5-heptatriene,[9] a reaction that has been proposed to occur in the rearrangement of calciferol to precalciferol.[10] Four years later, Johnson and Daoust suggested that Möbius benzene results from a “forbidden” conrotatory ring opening mode in Dewar benzene.[11] They realized that this reactive mode does not conform with the predictions from the Woodward–Hoffmann rules. However, in a more recent study it was reported that while the conrotatory mode is indeed preferred, Möbius benzene is not involved in the ring opening mode.[12] The “forbidden” disrotatory transition structure for the butadiene–cyclobutene conversion has been found to be a second-order saddle point.[13] High energy “forbidden” transition structures in [1, 7]-hydrogen shifts have also been reported.[14] In 2005, Rzepa proposed a Möbius twisted and Hückel aromatic 4n+ 2 electron electrocyclic transition-state structure for the ring opening/ring closure reaction of a (Z, E, Z)-decapentaene.[15] In contrast, Möbius aromatic transition states for electrocyclic reactions and which possess the Möbius strip topology have not been reported to date. Herein we report the first representative of this novel type of pericyclic reaction transition-state structure. Moreover, thermal ring opening in a Möbius twisted dodecahexaene is proposed to proceed preferably disrotatory via an aromatic transition state, rather than via the conrotatory transition structure predicted by the Woodward–Hoffmann rules for rings having the Hückel topology, and that is disfavored energetically by 19.9 kcal molÀ1 at the coupled-cluster level of theory![16]