Highly enantioselective oxidative couplings of 2-naphthols catalyzed by chiral bimetallic oxovanadium complexes with either oxygen or air as oxidant
Highly enantioselective oxidative couplings of 2-naphthols catalyzed by chiral bimetallic oxovanadium complexes with either oxygen or air as oxidant
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DOI：
10.1021/ja074322f
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发表时间：
2007-11-14
影响因子：
15
通讯作者：
Gong, Liu-Zhu
中科院分区：
文献类型：
--
作者：
Guo, Qi-Xiang;Wu, Zhi-Jun;Gong, Liu-Zhu
设计了手性双金属氧钒配合物，用于含C6和/或C7取代基的2-萘酚的对映选择性氧化偶联。利用紫外光谱、CID光谱和DFT计算发现，氧钒配合物2中存在从氨基酸向联苯轴的手性转移。l -异亮氨酸和非手性双酚合成的氧钒配合物加入5摩尔%，以氧为氧化剂，促进了双萘酚的均偶联反应，得到了几乎定量产率的双萘酚，对映选择性高达98%。由l -异亮氨酸和h -8-联萘酚衍生的氧钒配合物在催化2-萘酚的空气氧化偶联方面效率很高，对映选择性高达97% ee。V-51核磁共振研究表明，氧化钒配合物具有两种钒(V)形态。对反应进行了动力学研究、交叉偶联反应和HRMS谱研究，结果表明两种钒(V)均参与了催化反应，偶联反应在分子内发生自由基-自由基机制。量子力学计算合理化了s -氨基酸轴向手性匹配的协同效应对氧化偶联反应立体控制的重要性。该转化在制备手性配体和共轭聚合物中的应用证实了该方法在有机合成中的重要性。
The chiral bimetallic oxovanadium complexes have been designed for the enantioselective oxidative coupling of 2-naphthols bearing various substituents at C6 and/or C7. The chirality transferring from the amino acid to the axis of the biphenyl in oxovanadium complexes 2 was found to occur with the use of UV and CID spectra and DFT calculation. The homo-coupling reaction with oxygen as the oxidant was promoted by 5 mol % of an oxovanadium complex derived from L-isoleucine and achiral biphenol to afford binaphthols in nearly quantitative yields with high enantioselectivities of up to 98% ee. An oxovanadium complex derived from L-isoleucine and H-8-binaphthol is highly efficient at catalyzing the air-oxidized coupling of 2-naphthols with excellent enantioselectivities of up to 97% ee. V-51 NMR study shows that the oxovanadium complexes have two vanadium(V) species. Kinetic studies, the cross-coupling reaction, and HRMS spectral studies on the reaction have been carried out and illustrate that two vanadium(V) species are both involved in catalysis and that the coupling reaction undergoes a radical-radical mechanism in an intramolecular manner. Quantum mechanical calculations rationalize the importance of the cooperative effects of the axial chirality matching S-amino acids on the stereocontrol of the oxidative coupling reaction. The application of the transformation in the preparation of chiral ligands and conjugated polymers confirms the importance of the current process in organic synthesis.