New insight into the structure of organocuprate .pi.-complexes by determination of 13C,13C coupling constants
New insight into the structure of organocuprate .pi.-complexes by determination of 13C,13C coupling constants
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通过测定 13C,13C 偶联常数对有机铜配合物结构的新见解
DOI：
10.1021/ja00080a048
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发表时间：
1994
影响因子：
15
通讯作者：
A. Gerold
中科院分区：
文献类型：
--
作者：
N. Krause;R. Wágner;A. Gerold
在过去的二十年里，有机铜酸盐作为合成有机化学的工具，特别是非立体选择性合成，取得了显着的进展。[2]尽管与烯酮和烯酸酯的1，4-加成反应仍然是铜酸酯最重要的反应，1^共轭铜酸酯加成反应的合成潜力最近已被分别与2-烯-4-炔酸酯和2，4-二烯-6-炔酸酯的1，6-和1，8-加成反应所扩展，这为丰富官能化的异烯开辟了一条通用途径。3从机理的观点来看，这些反应表现出惊人的相似性：在所有情况下，在与羰基官能团相邻的CC双键处形成铜酸盐的-络合物，正如不同的基团4对于1，4-加成和我们5对于1，6-和1，8-加成反应所示。这些配合物的结构分配是基于在它们的13 C-NMR光谱中观察到的化学位移：铜原子与系统的协调引起CC双键的共振的大的upfeld位移，而铜酸盐簇的锂原子与羰基氧原子的相互作用引起羰基共振的小的downfield位移。4-6然而，这些研究有两个问题是不能令人满意的：（i）很难从化学位移中得出有关络合迈克尔受体的成键情况（键级、杂化）的结论;（ii）不能得到有关络合物中铜酸盐部分结构的信息。考虑到这些困难以及络合物形成对共轭铜酸盐加成反应机理和立体选择性的重要性，我们试图通过测定13 C，13 C偶合常数来获得有关铜酸盐络合物结构的额外信息，因为已知这些偶合常数对成键情况非常敏感。7据我们所知，迄今为止没有关于这类调查的报告。8
The past two decades have witnessed remarkable developments concerning the use of organocuprates as tools in synthetic organic chemistry, 1 particularly instereoselective synthesis. 2 Whereas the 1, 4-addition to enones and enoates is still the most important reaction of cuprates, 1^ the synthetic potential of conjugate cuprate additions has recently been extendedby the 1, 6-and1, 8-addition reactions to 2-en-4-ynoates and 2, 4-dien-6-ynoates, respectively, which open a versatile access to richly functionalized alienes. 3 From the mechanistic point of view, these reactions exhibit striking similarities: in all cases,-complexes of the cuprate at the CC double bond adjacent to the carbonyl function are formed, as has been shownby different groups4 for 1, 4-addition and by us5 for 1, 6-and1, 8-addition reactions. The structural assignment of these-complexes is based on the chemical shifts observed in their 13C-NMRspectra: coordination of a copper atom with the-system induces large upfleld shifts for the resonances of the CC double bond, whereas an interaction of a lithium atom of the cuprate cluster with the carbonyl oxygen atom causes small downfield shifts of the carbonyl resonances. 4-6 These investigations, however, are unsatisfactory with regard to two prob-lems:(i) it is difficult to draw conclusions about the bonding situation (bonding order, hybridization) of the complexed Michael acceptor from chemical shifts and (ii) no information about the structure of the cuprate part of the-complexes could be obtained. In view of these difficulties and of the importance of the-complex formation for the mechanismand consequently the stereoselec-tivities of conjugate cuprate additions, we sought to gain additional information aboutthe structure of cuprate-complexes by determination of13C, 13C coupling constants, sincethese are known to be very sensitive toward the bonding situation. 7 To the best of our knowledge, no investigations of this type have been reported so far. 8