Olefin metathesis involving ruthenium enoic carbene complexes
Olefin metathesis involving ruthenium enoic carbene complexes
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DOI：
10.1021/ja016386a
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发表时间：
2001-10-24
影响因子：
15
通讯作者：
Grubbs, RH
中科院分区：
文献类型：
--
作者：
Choi, TL;Lee, CW;Grubbs, RH
烯烃歧化反应在有机合成中已成为一种有价值的反应，许多天然产物的全合成中，烯烃歧化反应被频繁地用作关键的键结构。1随着最近发现的高活性催化剂1，通过交叉复分解(CM)有效地合成了三取代和官能化的烯烃，进一步扩大了该反应的底物范围。2随着这些成功的到来，人们探索出了前所未有的复分解反应。以前还没有关于R，β-不饱和羰基化合物通过复分解反应进行二聚反应的报道。钼和钨基催化剂与丙烯酸酯形成金属环丁烷，但由于羰基氧的络合作用，它们的活性不高。3本课题组报道了以非歧化路线合成了酯卡宾4，并表明4具有极强的活性。事实上，卡宾4是第一个开环环己烯的卡宾，但不是以催化方式进行反应。4酯卡宾4的合成不平凡，稳定性差，催化活性差，限制了其在有机合成中的应用。以往关于端烯与R，β-不饱和羰基化合物交叉歧化反应机理的报道称，催化剂1优先与端烯反应生成亚烷基，后者与R，β-不饱和羰基化合物交叉生成亚甲基和CM产物。2C当时，不稳定的烯酸卡宾5形成的可能性被认为较小。然而，最近人们发现，富电子催化剂1实际上能够在一定条件下与R，β-不饱和羰基化合物直接反应生成烯酸卡宾5。在这里，我们报道了第一次高效地在催化剂1(方案1)的作用下原位生成烯酸卡宾5，并成功地催化了先前不活跃的复分解底物的CM和开环反应。烯酸卡宾5的形成最初是在丙烯酸酯二聚生成富马酸酯的过程中发现的。最初的尝试
Olefin metathesis has become a valuable reaction in organic synthesis, as has been demonstrated by its frequent use as the key bond constructions for total syntheses of many natural products. 1 With the recent discovery of highly active catalyst 1, trisubstituted and functionalized alkenes have been synthesized efficiently by cross-metathesis (CM), further expanding the substrate scope for this reaction. 2 With these successes in hand, unprecedented metathesis reactions were explored. There have been no previous reports of the dimerization of R, β-unsaturated carbonyl compounds by a metathesis mechanism. Molybdenumand tungsten-based catalysts form metallocyclobutane with acrylates, but they are inactive due to carbonyl oxygen chelation. 3 Our group reported the synthesis of ester carbene 4 by a nonmetathesis route and showed that 4 was extremely reactive. In fact, ester carbene 4 was the first carbene to ring-open cyclohexene but did not react in a catalytic fashion. 4 The nontrivial synthesis, lack of stability, and the ineffective catalytic activity of ester carbene 4 has limited its uses in organic synthesis.Previous reports on the mechanism of cross-metathesis reactions between terminal olefins and R, β-unsaturated carbonyl compounds, state that catalyst 1 reacts preferentially with terminal olefins to form an alkylidene which crosses onto R, β-unsaturated carbonyl compounds to form methylidene and CM product. 2c At that time, the formation of the unstable enoic carbene 5 was believed to be less likely. However, it was recently discovered that the electron-rich catalyst 1 was, in fact, able to react with R, β-unsaturated carbonyl compounds directly to form enoic carbene 5 effectively under certain conditions. Herein, we report the first efficient generation of enoic carbenes 5 in situ with catalyst 1 (Scheme 1), and successful catalytic CM and ringopening reactions of previously inactive metathesis substrates. The formation of enoic carbene 5 was initially discovered in the dimerization of acrylates to form fumarates. Initial attempts