Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain.
J Am Chem Soc. 2014 Jan 22;136(3):1062-9. doi: 10.1021/ja410883p. Epub 2014 Jan 9.
In recent years a significant progress has been made for the carboxylation of aryl and benzyl halides with CO2, becoming convenient alternatives to the use of stoichiometric amounts of well-defined metal species. Still, however, most of these processes require the use of pyrophoric and air-sensitive reagents and the current methods are mostly restricted to organic halides. Therefore, the discovery of a mild, operationally simple alternate carboxylation that occurs with a wide substrate scope employing readily available coupling partners will be highly desirable. Herein, we report a new protocol that deals with the development of a synergistic activation of CO2 and a rather challenging activation of inert C(sp(2))-O and C(sp(3))-O bonds derived from simple and cheap alcohols, a previously unrecognized opportunity in this field. This unprecedented carboxylation event is characterized by its simplicity, mild reaction conditions, remarkable selectivity pattern and an excellent chemoselectivity profile using air-, moisture-insensitive and easy-to-handle nickel precatalysts. Our results render our method a powerful alternative, practicality and novelty aside, to commonly used organic halides as counterparts in carboxylation protocols. Furthermore, this study shows, for the first time, that traceless directing groups allow for the reductive coupling of substrates without extended π-systems, a typical requisite in many C-O bond-cleavage reactions. Taking into consideration the limited knowledge in catalytic carboxylative reductive events, and the prospective impact of providing a new tool for accessing valuable carboxylic acids, we believe this work opens up new vistas and allows new tactics in reductive coupling events.
近年来，在 CO2 与芳基和苄基卤化物的羧化方面取得了重大进展，成为使用化学计量的定义明确的金属物种的方便替代品。然而，这些过程大多数仍需要使用易燃和空气敏感的试剂，并且当前的方法主要限于有机卤化物。因此，发现一种温和、操作简单的替代羧化方法，具有广泛的底物范围，使用易得的偶联剂，将是非常理想的。在此，我们报告了一种新的方案，涉及协同激活 CO2 和相当具有挑战性的惰性 C(sp(2))-O 和 C(sp(3))-O 键的激活，这些键来自简单且廉价的醇，这是该领域以前未被认识到的机会。这种前所未有的羧化事件的特点是其简单性、温和的反应条件、显著的选择性模式以及使用空气不敏感、水分不敏感且易于处理的镍预催化剂的出色化学选择性。除了实用性和新颖性之外，我们的结果使我们的方法成为一种强大的替代方法，取代通常用于羧化方案的有机卤化物。此外，这项研究首次表明，无痕迹导向基团允许在没有扩展π系统的情况下进行底物的还原偶联，这是许多 C-O 键断裂反应的典型要求。考虑到催化羧基还原反应的知识有限，以及为获得有价值的羧酸提供新工具的预期影响，我们相信这项工作开辟了新的前景，并允许在还原偶联反应中采用新策略。
