Aromatic interactions as control elements in stereoselective organic reactions.
Aromatic interactions as control elements in stereoselective organic reactions.
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DOI：
10.1021/ar3000794
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发表时间：
2013-04-16
影响因子：
18.3
通讯作者：
Houk, K. N.
中科院分区：
文献类型：
--
作者：
Krenske, Elizabeth H.;Houk, K. N.
这个帐户描述了芳香环与其他基团的吸引力相互作用如何影响和控制许多反应的立体选择性。理论上的最新发展导致芳香相互作用建模的准确性提高。量子力学建模现在可以提供洞察这些相互作用的作用，在一个以前无法访问的细节水平，无论是基态物种和化学反应的过渡态。在这个帐户中，我们展示了过渡态建模如何导致发现芳基对几种类型的有机反应的立体选择性的影响。这些反应类型包括不对称二羟基化、转移氢化、杂Diels-桤木反应、酰基转移和Claisen重排。我们最近的研究导致了两类（4+3）环加成反应的一种新的机制图片，这两类反应都涉及呋喃与氧烯丙基中间体的反应。第一类环加成反应是由Hsung开发的，其特征是含有手性恶唑烷酮助剂的中性羟烯丙基。最初，这些环加成被认为依赖于平面中间体的两个面的差异空间拥挤。计算揭示了一个不同的图片，并表明，与呋喃的环加成优先发生通过更拥挤的过渡态，与呋喃添加在同一侧的恶唑烷酮的Ph取代基。拥挤过渡态由呋喃和Ph之间的CH-π相互作用稳定，价值约2.0 kcal/mol。立体控制在第二类（4+3）环加成，涉及手性烷氧基candyallyl阳离子，也是由有吸引力的相互作用与芳环控制。发现手性α-甲基苄醇衍生的烷氧基有利于拥挤过渡态，其中呋喃和Ar之间再次存在CH-π相互作用。阳离子环加成反应是逐步进行的，而Hsung环加成反应是协同进行的。我们的研究结果表明，这种形式的CH-π-定向立体控制是相当普遍的，很可能控制其他加成反应的立体选择性，其中一个平面中间体的一面带有一个悬垂的芳香族取代基。
This Account describes how attractive interaction of aromatic rings with other groups can influence and control the stereoselectivity of many reactions. Recent developments in theory have led to improved accuracy in the modeling of aromatic interactions. Quantum mechanical modeling can now provide insights into the roles of these interactions at a level of detail not previously accessible, both for ground-state species and for transition states of chemical reactions. In this Account, we show how transition-state modeling led to the discovery of the influence of aryl groups on the stereoselectivities of several types of organic reactions. These reaction types include asymmetric dihydroxylations, transfer hydrogenations, hetero-Diels–Alder reactions, acyl transfers, and Claisen rearrangements. Our recent studies have led to a novel mechanistic picture for two classes of (4+3) cycloadditions, both of which involve reactions of furans with oxyallyl intermediates. The first class of cycloadditions, developed by Hsung, features neutral oxyallyls containing a chiral oxazolidinone auxiliary. Originally, these cycloadditions were thought rely on differential steric crowding of the two faces of a planar intermediate. Computations reveal a different picture and show that cycloadditions with furan takes place preferentially through the more crowded transition state, with furan adding on the same side as the oxazolidinone’s Ph substituent. The crowded transition state is stabilized by a CH–π interaction between furan and Ph, worth about 2.0 kcal/mol. Stereocontrol in a second class of (4+3) cycloadditions, involving chiral alkoxy siloxyallyl cations, also is controlled by attractive interactions with aromatic rings. Alkoxy groups derived from chiral α-methylbenzyl alcohols are found to favor crowded transition states, where a CH–π interaction is again present between furan and Ar. The cationic cycloadditions are stepwise, while the Hsung cycloadditions are concerted. Our results suggest that this form of CH–π-directed stereocontrol is quite general and is likely to control the stereoselectivities of other addition reactions in which one face of a planar intermediate bears a pendant aromatic substituent.
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影响因子：
4.4
作者：
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通讯作者：
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影响因子：
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作者：
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通讯作者：
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通讯作者：
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