Structurally defined catalysts for enantioselective oxidative coupling reactions
Structurally defined catalysts for enantioselective oxidative coupling reactions
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DOI：
10.1002/anie.200351978
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发表时间：
2003-01-01
影响因子：
16.6
通讯作者：
Martell, AE
中科院分区：
文献类型：
--
作者：
Gao, J;Reibenspies, JH;Martell, AE
联苯二酚对映体及其衍生物是广泛的不对称合成的重要手性配体。[1]联苯酚的简单转化为2，2‘-(二苯基膦)-1，1’-联萘基(BINAP)尤其值得注意，因为BINAP极大地扩展了联苯酚在不对称催化中的合成用途。手性联苯酚的催化不对称合成及其相关催化剂对映体选择性的改善一直是许多研究者关注的问题。[3]现有的手性联二酚不对称制备催化剂包括手性胺或其衍生物的铜配合物[4]和具有一个或两个立体金属中心的手性活体配合物。[5]最近，二聚铜(II)配合物[4b，e，f]或双核活体配合物[5d，e]被证明是具有高对映选择性的较好催化剂。在上述报道中，催化金属络合物是通过手性配体与期望的金属离子(CuI、CuII或vivo)反应而原位制备的。一般来说，这种方法在溶液中至少产生三种物种：无金属配体、单核和双核配合物。然而，要确定对整体反应速度有贡献的活性物种并不容易。此外，上述催化剂的X-射线晶体结构从未被确定，这限制了旨在进一步提高催化对映体选择性和稳定性的机理研究。鉴于雅各布森的Salen催化剂[6]在广泛的不对称催化反应中的成功，我们决定研究偶联Salen络合物是否将催化需要两个催化中心的反应。本文介绍了一类用于2-萘酚不对称氧化偶联反应的双铜催化剂的合成和晶体结构。在CuII存在下，(1R，2R)-1，2-二氨基环己烷(R，RDACH)与2，6-二甲基苯酚或其衍生物反应生成黄绿色的1a-c固体(方案1)，
Pure binaphthol enantiomers and their derivatives are important chiral ligands for a wide range of asymmetric syntheses.[1] The facile conversion of binaphthol into 2, 2’-(diphenylphosphanyl)-1, 1’-binaphthyl (BINAP) is particularly noteworthy because BINAP greatly expanded the synthetic utilities of binaphthol in asymmetric catalysis.[2] In light of the wide-ranging and important applications of these compounds, catalytic asymmetric preparation of chiral binaphthols and improvements in the enantioselectivity of the associated catalysts have continued to attract the attention of many researchers.[3]Existing catalysts for the asymmetric preparation of chiral binaphthols include copper complexes of chiral amines or their derivatives [4] and chiral VIVO complexes with either one or two stereogenic metal centers.[5] Recently, dimeric copper (ii) complexes [4b, e, f] or dinuclear VIVO complexes [5d, e] have been shown to be better catalysts with a high enantioselectivity. In the above reports, the catalytic metal complexes were prepared in situ by reacting a chiral ligand with a desired metal ion (CuI, CuII, or VIVO). Generally, this method produces at least three species in solution: metal-free ligand, mononuclear, and dinuclear complexes. However, it is not easy to identify the active species that contribute to the overall reaction rate. Furthermore, the X-ray crystal structures of the above catalysts have never been determined, and this has restricted mechanistic investigations aimed at further improving the catalytic enantioselectivity and robustness. Given the success of Jacobsen's salen catalysts [6] in a broad range of asymmetric catalytic reactions, we decided to investigate whether coupled salen complexes would catalyze reactions that require two catalytic centers. Herein we describe the syntheses and crystal structures of a family of dicopper catalysts for the asymmetric oxidative coupling of 2-naphthol. The reaction of (1R, 2R)-1, 2-diaminocyclohexane (R, RDACH) with 2, 6-diformylphenol or its derivatives in the presence of CuII gave yellow-green solids of 1a–c (Scheme 1),