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Formal [3 + 2] Cycloadditions via Indole Activation: A Route to Pyrroloindolines and Furoindolines

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posted on 18.07.2016 by Ya-Ni Wang, Tian-Ren Li, Mao-Mao Zhang, Bei-Yi Cheng, Liang-Qiu Lu, Wen-Jing Xiao
Here, we describe a novel [3 + 2] cycloaddition of 3-substituted indoles with vinyl aziridines and vinyl epoxides that provides a straightforward approach to pyrroloindolines and furoindolines bearing vinyl groups (up to 96% yield and 9:1 dr). In contrary to previous reports involving Lewis acid activation, this work reports successful reactions based on the activation of indole using t-BuOK and BEt3 (triethylborane), thereby preserving the free N–H group on indoles. In addition, a gram-scale reaction and a ring-closing metatheis reaction are performed to provide good demonstrations of the synthetic utility of this approach.