Gold-Catalyzed Rearrangements: Reaction Pathways Using 1-Alkenyl-2-alkynylcyclopropane Substrates
Gold-Catalyzed Rearrangements: Reaction Pathways Using 1-Alkenyl-2-alkynylcyclopropane Substrates
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DOI：
10.1002/anie.201007795
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Tomas, Miguel
中科院分区：
文献类型：
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作者：
Barluenga, Jose;Tudela, Eva;Tomas, Miguel
在过去的十年中，均相金催化通过大量新颖的转化突破了有机化学领域。 [1]特别是，金催化剂活化炔烃、烯烃或丙二烯的能力能够实现深刻的骨架重排。 [2]尽管金催化的 1, n-烯炔环异构化反应已得到广泛发展，[3] 但环丙烷单元作为 C-3 替代物参与金属催化环异构化反应的研究却少得多。例如，简单的炔基环丙烷在胺[4]或二苯亚砜[5]存在下会发生金催化的环丙烷-环丁烷扩环反应。具有附加官能团（羟基、[6]酰基、[7]或环氧基[8]）的炔基环丙烷允许基于环丙烷环的裂解设计有用的转化。在这种情况下，我们认为含有烯烃-环丙烷-炔连接的底物的催化转化可能是一种有前途的方法。令人惊讶的是，基于 1-烯基-2-炔基环丙烷骨架（1, 5-烯炔排列）的转化非常罕见。[9, 10] 因此，Toste 及其同事 [9a] 报道了金 (I) 催化的顺式-PivO-乙烯基-炔基-环丙烷单元环异构化为芳烃和环庚三烯衍生物： 5-endo-dig 和 6-endo-dig 环化反应（方案 1a）。我们最近的报告 [11] 关于直接获取 6-炔基双环 [3.1。 0] hexen-2-enes 1 促使我们研究它们对金属催化的行为。尽管该结构具有所需的顺式烯烃-环丙烷-炔连接性，但烯基功能被限制在环状子结构中这一事实可能会带来新的反应途径。据报道，1）金（I）催化化合物1的环异构化，2）在不存在/存在亲核试剂的情况下观察到不同的结构重排（方案1b）。经过一些优化研究，我们发现原位生成的阳离子JohnPhos-金（I）络合物催化炔基环丙烷1a的环异构化，从而以合成有用的收率（75%；方案 2）提供炔基环己二烯 2a。 [12]化合物2a的结构是在一维和二维NMR数据的基础上阐明的，并通过对已知芳烃4a的芳构化来证实。 [13]
In the past decade, homogeneous gold catalysis have irrupted in organic chemistry with a vast array of novel transformations.[1] In particular, the ability of gold catalysts to activate alkynes, alkenes, or allenes enables profound skeletal rearrangements.[2] Whereas gold-catalyzed 1, n-enyne cycloisomerization reactions have been extensively developed,[3] the involvement of the cyclopropane unit as a C-3 surrogate in metal-catalyzed cycloisomerization reactions has been much less studied. For instance, simple alkynylcyclopropanes undergo gold-catalyzed cyclopropane–cyclobutane ring expansion in the presence of amines [4] or diphenylsulfoxide.[5] Alkynylcyclopropanes with additional functionalities (hydroxy,[6] acyl,[7] or epoxy [8]) allowed to design useful transformations based on the cleavage of the cyclopropane ring. In this scenario, it seemed to us that the catalytic transformations of substrates containing the alkene–cyclopropane–alkyne connectivity might be a promising approach. Surprisingly, transformations based on the 1-alkenyl-2-alkynylcyclopropane framework (1, 5-enyne arrangement) are very rare.[9, 10] Thus, Toste and co-workers [9a] reported the gold (I)-catalyzed cycloisomerization of cis-PivO-vinyl-alkynyl-cyclopropane units into arene and cycloheptatriene derivatives through 5-endo-dig and 6-endo-dig cyclization reactions (Scheme 1a). Our recent report [11] on a straightforward access to 6-alkynylbicylo [3.1. 0] hexen-2-enes 1 prompted us to study their behavior toward metal catalysis. Although this structure features the required cis-alkene–cyclopropane–alkyne connectivity, the fact that the alkenyl function is constrained in a cyclic substructure would likely impose new reaction pathways. Herein, it is reported that 1) gold (I) catalyzes the cycloisomerization of compounds 1 and, 2) divergent structural rearrangements are observed in the absence/presence of nucleophiles (Scheme 1b).After some optimization studies, we found that an in situ generated cationic JohnPhos–gold (I) complex catalyzes the cycloisomerization of the alkynylcyclopropane 1a, thus affording the alkynylcyclohexadiene 2a in synthetically useful yield (75%; Scheme 2).[12] The structure of compound 2a was elucidated on the basis of one-and two-dimensional NMR data and confirmed by aromatization to the known arene 4a.[13]