Rhodium-catalyzed C-C bond formation via heteroatom-directed C-H bond activation.
Rhodium-catalyzed C-C bond formation via heteroatom-directed C-H bond activation.
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DOI：
10.1021/cr900005n
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发表时间：
2010-02-10
期刊：
影响因子：
62.1
通讯作者：
Ellman, Jonathan A.
中科院分区：
文献类型：
--
作者：
Colby, Denise A.;Bergman, Robert G.;Ellman, Jonathan A.
在过去的十年里，有机金属化学中的CH键活化反应被认为是有机金属化学中的“圣杯”，在合成上有用的反应越来越多地被开发和应用于天然产物和药物合成。1烃类的普遍存在和相对低的成本使得CH键官能化成为经典CC键形成反应（如交叉偶联）的有吸引力的替代方案，后者需要有机卤化物和有机金属试剂。2除了为标准的交叉偶联策略提供原子经济的替代方案外，CH键官能化还减少了有毒副产物的产生，从而有助于在减少环境影响的情况下不断增长的反应领域。在通过CH活化机制进行的CC键形成反应领域，铑催化剂因其官能团耐受性和广泛的合成用途而脱颖而出。在过去的十年中，许多铑催化的杂原子定向CH键官能化的方法已被报道，将是本综述的重点。2001年以前文献中出现的材料已经过审查，必要时只作为背景介绍。从相对简单的前体合成复杂分子一直是许多有机化学家的目标。以最小的预活化选择性地官能化分子的能力可以简化合成，并扩大探索复杂分子在从制药工业到材料科学等领域的效用的机会。事实上，选择性问题在所有CH键官能化方法的开发中是至关重要的。几个研究小组已经开发出了在具有许多空间和电子相似的CH键的分子中实现选择性的巧妙方法。[3]在《化学评论》的这期特刊中，我们将在随附的文章中详细讨论其中的许多方法。已经看到广泛成功的一种方法涉及使用近端杂原子，其用作特定CH键的选择性官能化的导向基团。在调查的例子杂原子导向的铑催化，两个不同的反应机理的途径被揭示。在一种情况下，杂原子充当螯合剂以结合Rh催化剂，促进近端位点处的反应性（图1A）。在这种情况下，五元金属配位化合物的形成提供了在所需位置诱导反应性的有利驱动力。在另一种情况下，杂原子最初与Rh催化剂配位，然后起作用以稳定在近端位点形成金属-碳键（图1B）。几个小组已经证明了CH键官能化反应对复杂分子合成的适用性。4.靶向合成提供了一个平台来测试方法在独特的化学和空间环境中的有效性。在这方面，Rh催化的CH键官能化方法脱颖而出，在文献中描述了几种在关键步骤中利用CH键官能化的合成。这些合成强调以下的方法，他们采用的讨论。
Once considered the “holy grail” of organometallic chemistry, synthetically useful reactions employing CH bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. 1 The ubiquity and relatively low cost of hydrocarbons makes CH bond functionalization an attractive alternative to classical CC bond forming reactions such as crosscoupling, which require organohalides and organometallic reagents. 2 In addition to providing an atom economical alternative to standard cross-coupling strategies, CH bond functionalization also reduces the production of toxic byproducts, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of CC bond forming reactions that proceed via a CH activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the past decade, many Rh-catalyzed methods for heteroatom-directed CH bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. 1a-c The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal preactivation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all CH bond functionalization methods. Several groups have developed elegant approaches toward achieving selectivity in molecules that possess many sterically and electronically similar CH bonds. 3 Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical ReViews. One approach that has seen widespread success involves the use of a proximal heteroatom that serves as a directing group for the selective functionalization of a specific CH bond. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site (Figure 1A). In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site (Figure 1B).A true test of the utility of a synthetic method is in its application to the synthesis of natural products or complex molecules. Several groups have demonstrated the applicability of CH bond functionalization reactions toward complex molecule synthesis. 4 Target-oriented synthesis provides a platform to test the effectiveness of a method in unique chemical and steric environments. In this respect, Rhcatalyzed methods for CH bond functionalization stand out, with several syntheses being described in the literature that utilize CH bond functionalization in a key step. These syntheses are highlighted following the discussion of the method they employ.
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3.6
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