Department of Chemistry, Federal University of Minas Gerais, Belo Horizonte, 31270-901, MG, Brazil.
Department of Chemistry, Fluminense Federal University, Niteroi, 24020-141, RJ, Brazil.
Chemistry. 2021 Sep 1;27(49):12453-12508. doi: 10.1002/chem.202101004. Epub 2021 Jul 13.
Synthetic organic chemistry has witnessed a plethora of functionalization and defunctionalization strategies. In this regard, C-H functionalization has been at the forefront due to the multifarious applications in the development of simple to complex molecular architectures and holds a brilliant prospect in drug development and discovery. Despite been explored tremendously by chemists, this functionalization strategy still enjoys the employment of novel metal catalysts as well metal-free organic ligands. Moreover, the switch to photo- and electrochemistry has widened our understanding of the alternative pathways via which a reaction can proceed and these strategies have garnered prominence when applied to C-H activation. Synthetic chemists have been foraging for new directing groups and templates for the selective activation of C-H bonds from a myriad of carbon-hydrogen bonds in aromatic as well as aliphatic systems. As a matter of fact, by varying the templates and directing groups, scientists found the answer to the challenge of distal C-H bond activation which remained an obstacle for a very long time. These templates have been frequently harnessed for selectively activating C-H bonds of natural products, drugs, and macromolecules decorated with multiple C-H bonds. This itself was a challenge before the commencement of this field as functionalization of a site other than the targeted site could modify and hamper the biological activity of the pharmacophore. Total synthesis and pharmacophore development often faces the difficulty of superfluous reaction steps towards selective functionalization. This obstacle has been solved by late-stage functionalization simply by harnessing C-H bond activation. Moreover, green chemistry and metal-free reaction conditions have seen light in the past few decades due to the rising concern about environmental issues. Therefore, metal-free catalysts or the usage of non-toxic metals have been recently showcased in a number of elegant works. Also, research groups across the world are developing rational strategies for directing group free or non-directed protocols that are just guided by ligands. This review encapsulates the research works pertinent to C-H bond activation and discusses the science devoted to it at the fundamental level. This review gives the readers a broad understanding of how these strategies work, the execution of various metal catalysts, and directing groups. This not only helps a budding scientist towards the commencement of his/her research but also helps a matured mind searching out for selective functionalization. A detailed picture of this field and its progress with time has been portrayed in lucid scientific language with a motive to inculcate and educate scientific minds about this beautiful strategy with an overview of the most relevant and significant works of this era. The unique trait of this review is the detailed description and classification of various directing groups and their utility over a wide substrate scope. This allows an experimental chemist to understand the applicability of this domain and employ it over any targeted substrate.
合成有机化学已经见证了大量的功能化和去功能化策略。在这方面,由于在开发简单到复杂分子结构中的广泛应用,C-H 功能化一直处于前沿地位,并在药物开发和发现中具有广阔的前景。尽管化学家已经对此进行了极大的探索,但这种功能化策略仍然需要使用新型金属催化剂和无金属有机配体。此外,向光化学和电化学的转变拓宽了我们对反应可以进行的替代途径的理解,并且这些策略在 C-H 活化中得到了重视。合成化学家一直在寻找新的导向基团和模板,以选择性地激活芳香族和脂肪族体系中无数碳氢键中的 C-H 键。事实上,通过改变模板和导向基团,科学家们找到了挑战的答案,即长期以来一直是障碍的远程 C-H 键活化。这些模板经常被用于选择性地激活天然产物、药物和带有多个 C-H 键的大分子的 C-H 键。在这个领域开始之前,这本身就是一个挑战,因为除了目标位点之外的功能化会修饰和阻碍药效团的生物活性。全合成和药效团开发经常面临着对选择性功能化的多余反应步骤的困难。通过晚期功能化简单地利用 C-H 键活化,这个障碍已经得到了解决。此外,由于对环境问题的日益关注,过去几十年中绿色化学和无金属反应条件已经出现。因此,最近在许多优雅的作品中展示了无金属催化剂或使用无毒金属。此外,世界各地的研究小组正在开发无导向基团或非导向协议的合理策略,这些策略仅由配体引导。本综述总结了与 C-H 键活化相关的研究工作,并在基础层面上讨论了致力于该领域的科学。本综述使读者广泛了解这些策略的工作原理、各种金属催化剂和导向基团的执行情况。这不仅有助于一个崭露头角的科学家开始他/她的研究,也有助于一个成熟的头脑寻找选择性功能化。本综述以清晰的科学语言描绘了该领域及其随时间的发展的全貌,目的是向科学头脑灌输和教育关于这种美丽策略的知识,并概述这个时代最相关和最重要的工作。本综述的独特之处在于对各种导向基团的详细描述和分类,以及它们在广泛的底物范围内的应用。这允许实验化学家了解该领域的适用性,并在任何目标底物上使用它。