Gold-catalyzed rearrangements and beyond.
Gold-catalyzed rearrangements and beyond.
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DOI：
10.1021/ar400174p
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发表时间：
2014-03-18
影响因子：
18.3
通讯作者：
Echavarren, Antonio M.
中科院分区：
文献类型：
--
作者：
Obradors, Carla;Echavarren, Antonio M.
烯炔的环异构化反应可能是亲电金属配合物催化的最具代表性的碳-碳键形成反应。这些转化在合成上是有用的，因为化学家可以用它们在温和的条件下从容易组装的起始材料构建复杂的结构。然而，这些转变可能具有复杂的机制。一般而言，金（I）在任何其它不饱和官能团存在下通过形成（η2-炔）-金络合物来活化炔。这种物质容易与亲核试剂反应，包括富电子烯烃。在这种情况下，反应形成环丙基金（I）卡宾样中间体。这些可以来自不同的途径，这取决于炔和烯烃的取代模式。在不存在外部亲核试剂的情况下，1，n-烯炔可以在完全分子内反应中形成骨架重排产物，这与由Grubbs型卡宾或其他相关金属卡宾的[2 + 2]环加成引发的复分解反应在机理上非常不同。在这个帐户中，我们讨论如何环异构化和加成反应的取代烯炔，以及分子间的反应，炔和烯烃，最好的解释为通过离散的阳离子中间体，其中金（I）起着重要的作用，在稳定的正电荷进行。最重要的中间体是高度离域的阳离子物种，一些化学家将其描述为环丙基金（I）卡宾或金（I）稳定的环丙基甲基/环丁基/高烯丙基碳阳离子。然而，我们更喜欢环丙基金（I）卡宾配方，因为它的简单性和记忆值，突出了这些中间体与烯烃进行环丙烷化反应的趋势。在金（I）的存在下，通过分子内或分子间反应，我们可以将各种杂亲核试剂和亲碳亲核试剂加成到烯炔上，通过立体特异性反加成反应，得到相应的高立体选择性加成物。我们还开发了立体定向合成加成，这可能是通过类似的中间体发生。羰基攻击中间体环丙基金（I）卡宾的环丙基碳引发了一组特别有趣的反应。这些引发级联转化，可导致形成两个C-C键和一个C-O键。在完全分子内过程中，这种立体特异性转化已被应用于天然倍半萜类化合物的合成，如（+）-orientalol F和（−）-englerin A。环丙基金（I）卡宾与烯烃的分子内和分子间捕获导致环丙烷的形成，分子复杂性显著增加，特别是在该过程与炔丙基烷氧基和相关OR基团的迁移相结合的情况下。我们最近已经证明了这一点，在立体选择性全合成的抗病毒倍半萜（+）-schisanwilsonene环化/1，5-乙酰氧基迁移/分子间环丙烷化。在该合成中，环化/1，5-乙酰氧基迁移比将导致外消旋化的替代1，2-酰氧基迁移更快。
Cycloisomerizations of enynes are probably the most representative carbon–carbon bond forming reactions catalyzed by electrophilic metal complexes. These transformations are synthetically useful because chemists can use them to build complex architectures under mild conditions from readily assembled starting materials. However, these transformations can have complex mechanisms. In general, gold(I) activates alkynes in the presence of any other unsaturated functional group by forming an (η2-alkyne)–gold complex. This species reacts readily with nucleophiles, including electron-rich alkenes. In this case, the reaction forms cyclopropyl gold(I) carbene-like intermediates. These can come from different pathways depending on the substitution pattern of the alkyne and the alkene. In the absence of external nucleophiles, 1,n-enynes can form products of skeletal rearrangement in fully intramolecular reactions, which are mechanistically very different from metathesis reactions initiated by the [2 + 2] cycloaddition of a Grubbs-type carbene or other related metal carbenes. In this Account, we discuss how cycloisomerization and addition reactions of substituted enynes, as well as intermolecular reactions between alkynes and alkenes, are best interpreted as proceeding through discrete cationic intermediates in which gold(I) plays a significant role in the stabilization of the positive charge. The most important intermediates are highly delocalized cationic species that some chemists describe as cyclopropyl gold(I) carbenes or gold(I)-stabilized cyclopropylmethyl/cyclobutyl/homoallyl carbocations. However, we prefer the cyclopropyl gold(I) carbene formulation for its simplicity and mnemonic value, highlighting the tendency of these intermediates to undergo cyclopropanation reactions with alkenes. We can add a variety of hetero- and carbonucleophiles to the enynes in the presence of gold(I) in intra- or intermolecular reactions, leading to the corresponding adducts with high stereoselectivity through stereospecific anti-additions. We have also developed stereospecific syn-additions, which probably occur through similar intermediates. The attack of carbonyl groups at the cyclopropyl carbons of the intermediate cyclopropyl gold(I) carbenes initiates a particularly interesting group of reactions. These trigger a cascade transformation that can lead to the formation of two C–C and one C–O bonds. In the fully intramolecular process, this stereospecific transformation has been applied for the synthesis of natural sesquiterpenoids such as (+)-orientalol F and (−)-englerin A. Intra- and intermolecular trapping of cyclopropyl gold(I) carbenes with alkenes leads to the formation of cyclopropanes with significant increase in the molecular complexity, particularly in cases in which this process combines with the migration of propargylic alkoxy and related OR groups. We have recently shown this in the stereoselective total synthesis of the antiviral sesquiterpene (+)-schisanwilsonene by a cyclization/1,5-acetoxy migration/intermolecular cyclopropanation. In this synthesis, the cyclization/1,5-acetoxy migration is faster than the alternative 1,2-acyloxy migration that would result in racemization.
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影响因子：
15
作者：
Chatani, N;Kataoka, K;Seki, Y
通讯作者：
Seki, Y
影响因子：
2.3
作者：
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通讯作者：
Gagosz, Fabien
影响因子：
2.8
作者：
Chatani, N;Furukawa, N;Murai, S
通讯作者：
Murai, S
影响因子：
15
作者：
Horino Y;Yamamoto T;Ueda K;Kuroda S;Toste FD
通讯作者：
Toste FD
影响因子：
4.3
作者：
Escribano-Cuesta, Ana;Lopez-Carrillo, Veronica;Echavarren, Antonio M.
通讯作者：
Echavarren, Antonio M.