Cooperative activation of cyclobutanones and olefins leads to bridged ring systems by a catalytic [4 + 2] coupling
作者:Haye Min Ko、Guangbin Dong
DOI:10.1038/nchem.1989
日期:2014.8
Bridged ring systems are widely found in natural products, and successful syntheses of them frequently feature intramolecular DielsâAlder reactions. These reactions are subclassified as either type I or type II depending on how the diene motif is tethered to the rest of the substrate (type I are tethered at the 1-position of the diene and type II at the 2-position). Although the type I reaction has been used with great success, the molecular scaffolds accessible by the type II reactions are limited by the strain inherent in the formation of an sp2 carbon at a bridgehead position. Here, we describe a complementary approach that provides access to these structures through the CâC activation of cyclobutanones and their coupling with olefins. Various alkenes have been coupled with cyclobutanones to provide a range of bridged skeletons. The ketone group of the products serves as a convenient handle for downstream functionalization. Although widely used to form bridged ring systems, certain intramolecular DielsâAlder reactions are hampered by the strain inherent in forming an sp2-carbon at a bridgehead position. Now, an alternative strategy has been described to access these bridged ring systems through the CâC activation and coupling of cyclobutanones with olefins.
桥环系统广泛存在于天然产物中,成功合成桥环系统的方法通常是分子内 DielsâAlder 反应。根据二烯基团与底物其他部分的连接方式,这些反应又可分为 I 型和 II 型(I 型是在二烯的 1 位连接,II 型是在 2 位连接)。虽然 I 型反应取得了巨大成功,但 II 型反应所能获得的分子支架受到了桥头位置形成 sp2 碳所固有的应变的限制。在这里,我们将介绍一种补充方法,通过环丁酮的 CâC 活化及其与烯烃的偶联来获得这些结构。各种烯烃与环丁酮的偶联提供了一系列桥接骨架。产物中的酮基可以方便地进行下游官能化。虽然桥环体系被广泛应用于形成桥环体系,但某些分子内 DielsâAlder 反应会受到在桥头位置形成 sp2 碳所固有的应变的影响。现在,一种通过环丁酮与烯烃的 CâC 活化和偶联来获得这些桥环体系的替代策略已经问世。