Bijvoet in solution reveals unexpected stereoselectivity in a Michael addition.
Bijvoet in solution reveals unexpected stereoselectivity in a Michael addition.
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DOI：
10.1002/chem.201002520
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发表时间：
2011-02
期刊：
影响因子：
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通讯作者：
Han Sun;Edward J. d'Auvergne;U. Reinscheid;L. Dias;C. K. Andrade;Rafael O. Rocha;C. Griesinger
中科院分区：
文献类型：
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作者：
Han Sun;Edward J. d'Auvergne;U. Reinscheid;L. Dias;C. K. Andrade;Rafael O. Rocha;C. Griesinger
用Bijvoet（1951）所示的异常x射线衍射可以确定小结晶分子的绝对构型。对于大多数既不能结晶又不易转化为可结晶衍生物的化合物，仍然需要立体控制有机合成来建立它们的绝对构型。在这一贡献，一个新的基本方法来解决绝对构型将提出，不需要结晶。利用残余偶极耦合增强的核磁共振光谱，可以创建有限数量的结构集合，反映正确的构象和相对构型。随后，从这些系综中，通过DFT计算预测了旋光色散（ORD）光谱，并与实验结果进行了比较。这两个步骤的结合揭示了溶液中柔性分子的绝对构型，这是在没有核磁共振波谱的情况下对热学方法和DFT的一大挑战。本文将用新方法阐明由铌(V)手性烯酸酯合成的新Michael加成产物的绝对立体化学。
The absolute configuration of small crystallizable molecules can be determined with anomalous X-ray diffraction as shown by Bijvoet in 1951. For the majority of compounds that can neither be crystallized nor easily be converted into crystallizable derivatives, stereocontrolled organic synthesis is still required to establish their absolute configuration. In this contribution, a new fundamental methodology for resolving the absolute configuration will be presented that does not require crystallization. With residual dipolar coupling enhanced NMR spectroscopy, ensembles of a limited number of structures are created reflecting the correct conformations and relative configuration. Subsequently, from these ensembles, optical rotation dispersion (ORD) spectra are predicted by DFT calculations and compared to experimental results. The combination of these two steps reveals the absolute configuration of a flexible molecule in solution, which is a big challenge to chiroptical methods and DFT in the absence of NMR spectroscopy. Here the absolute stereochemistry of the product of a new Michael addition, synthesized via a niobium(V) chiral enolate, will be elucidated by using the new methodology.