Department of Chemical Sciences, Tezpur University, Napaam, Tezpur, Assam, India-784028.
Org Biomol Chem. 2021 Aug 21;19(31):6761-6765. doi: 10.1039/d1ob01030a. Epub 2021 Jul 21.
Herein, we report that the trifluoroethanol-mediated ring-opening cyclization of readily accessible 4-(2-oxiranylmethoxy)indoles takes place in a diastereoselective and 6-endo fashion to generate pyrano[2,3-e]indol-3-ols in high yields. This regioselective cyclization at the indole C-5 position requires the presence of a π-activating aryl substituent on the reacting epoxide carbon atom, but remains uninfluenced by the electronic nature of the indole-N-substituent. Interestingly, blocking the C-5 position of the indole unit directs the reaction to generate oxepino[4,3,2-cd]indol-3-ols via 7-endo epoxide-arene cyclization.
在此，我们报告了一种通过三氟乙醇介导的易于获得的 4-(2-环氧乙烷基甲氧基)吲哚的开环环化反应，该反应以非对映选择性和 6-endo 方式进行，以高产率生成吡喃并[2,3-e]吲哚-3-醇。这种吲哚 C-5 位置的区域选择性环化需要在反应环氧碳原子上存在一个 π-活化的芳基取代基，但不受吲哚-N-取代基的电子性质的影响。有趣的是，封闭吲哚单元的 C-5 位置会导致反应通过 7-endo 环氧化合物-芳环环化生成氧杂氮杂[4,3,2-cd]吲哚-3-醇。
