作者:Takuya Hashimoto、Yu Kawamata、Keiji Maruoka
DOI:10.1038/nchem.1998
日期:2014.8
A diverse array of chiral organocatalysts have been developed that rely on acidâbase interactions to promote enantioselective ionic reactions via the movement of electron pairs. The stereocontrol of radical reactions using organocatalysts is an alternative approach, and several studies have shown that synthetically useful reactivity can result by controlling the movement of single electrons. However, in these studies, it is still an acidâbased organocatalyst which forms a closed-shell intermediate with substrate prior to the radical reaction and imparts chiral information, and use of a chiral organic radical directly as catalyst has only rarely been explored. Here, we report the design of an organic thiyl radical catalyst with a carefully designed chiral pocket constructed around a chiral thiol precatalyst. The resulting catalyst was used to effect highly diastereo- and enantioselective CâC bond-forming radical cyclizations. The ability of thiyl radicals to promote reactions has been known for decades although its extension to asymmetric catalysis has only rarely been explored. Now, an organic thiyl radical catalyst with a carefully structured chiral pocket has been designed as a means to achieve highly enantioselective radical cyclizations.
目前已开发出多种手性有机催化剂,它们依靠酸碱相互作用,通过电子对的移动促进对映选择性离子反应。利用有机催化剂对自由基反应进行立体控制是另一种方法,一些研究表明,通过控制单个电子的移动可以产生对合成有用的反应。然而,在这些研究中,仍然是酸基有机催化剂在自由基反应之前与底物形成闭壳中间体并传递手性信息,而直接使用手性有机自由基作为催化剂的研究还很少。在此,我们报告了一种有机硫基催化剂的设计,该催化剂围绕手性硫醇前催化剂精心设计了一个手性口袋。由此产生的催化剂可用于实现高度非对映和对映选择性的 CâC 键形成自由基环化反应。巯基促进反应的能力已为人所知数十年,但其在不对称催化方面的应用却鲜有探索。现在,我们设计出了一种具有精心构造的手性口袋的有机硫基催化剂,作为实现高对映选择性自由基环化反应的一种手段。