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首页> 外文期刊>Chemistry: A European journal >On the Dichotomic Reactivity of Lithiated Styrene Oxide: A Computational and Multinuclear Magnetic Resonance Investigation
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On the Dichotomic Reactivity of Lithiated Styrene Oxide: A Computational and Multinuclear Magnetic Resonance Investigation

机译：锂化苯乙烯氧化物的二分反应性：计算和多核磁共振研究

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摘要

A multinuclear magnetic resonance investigation, supported by density functional theory calculations, has been synergically used to investigate the configurational stability, reactivity and aggregation states of a-lithiated styrene oxide in THF at 173 K. NMR studies on a-lithiated [α,β-~(13)C_2]styrene oxide (also in an enantiomerically enriched form) proved that in THF this oxiranyllithium is mainly present as a solvated monomeric species in equilibrium with a complex mixture of stereoisomeric dimeric aggregates, as well as with bridged and tetrameric aggregates. The fact that some C_V-Li bonds are partially broken in some stereoisomers reduces their symmetry and complicates the NMR spectra: two diastereoisomers each having a pair of diastereotopic carbon atoms slowly inverting at the lithium atom in absence of tetramethylethylenediamine (TMEDA) have been detected. A (~(13)C,~7Li)-HMQC experiment to correlate ~7Li and ~(13)C resonances of the various aggregates has been performed for the first time. From natural bond analysis, the monomeric aggregate was proven to have a lower carbenoid character with respect to bridged O-coordinated dimeric aggregates. The employment of suitable experimental conditions in terms of concentration, temperature and the presence or not of TMEDA are crucial to mitigate at the best the “carbenelike” reactivity of lithiated styrene oxide toward intermolecular CLi insertions, eliminative dimerisation reactions and ring-opening reactions. A two-step mechanism for the deprotonation of styrene oxide by sBuLi in THF has been proposed and discussed as well as competitive side reactions.
机译：在密度泛函理论计算的支持下，多核磁共振研究已被协同用于研究173 K下THF中a-锂化苯乙烯氧化物的构型稳定性，反应性和聚集态。a-锂化[α，β- 〜（13）C_2]环氧乙烷（也是对映体富集的形式）证明，在四氢呋喃中，该环氧乙烷基锂主要以溶剂化的单体形式存在，与立体异构二聚体聚集体的复杂混合物以及桥联和四聚体聚集体处于平衡状态。一些C_V-Li键在某些立体异构体中部分断裂的事实降低了它们的对称性并使NMR光谱复杂化：已检测到两种非对映异构体，每个非对映异构体均具有一对非对映体碳原子，在不存在四甲基乙二胺（TMEDA）的情况下在锂原子上缓慢反转。首次进行了（〜（13）C，〜7Li）-HMQC实验以关联各种聚集体的〜7Li和〜（13）C共振。通过自然键分析，证明单体聚集体相对于桥连的O配位二聚体聚集体具有较低的类胡萝卜素特性。就浓度，温度和是否存在TMEDA而言，采用合适的实验条件对于最大程度地减轻锂化聚环氧乙烷对分子间CLi插入，消除性二聚反应和开环反应的“卡宾”反应至关重要。已经提出并讨论了由sBuLi在THF中使氧化苯乙烯质子化的两步机理以及竞争性副反应。

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