Tanaka Hiroki, Yasui Toshihiro, Uyanik Muhammet, Ishihara Kazuaki
Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan.
Org Lett. 2023 Apr 14;25(14):2377-2381. doi: 10.1021/acs.orglett.3c00207. Epub 2023 Feb 27.
We serendipitously found an unprecedented 5-to-7-membered ring expansion of 2-alkylspiroindolenines to azepinoindoles mediated by -tetrabutylammonium fluoride. The starting materials can be easily prepared by the hypoiodite-catalyzed oxidative dearomative spirocyclization of indole derivatives. Mildly basic conditions and electron-deficient protecting groups for the amines were found to be crucial to promoting chemoselective reactions. Moreover, the ring expansion of aniline-derived spiroindolenines proceeds smoothly under much milder conditions using only a catalytic amount of cesium carbonate.
我们意外地发现，在四丁基氟化铵的介导下，2-烷基螺吲哚啉可发生前所未有的5至7元环扩展反应，生成氮杂环庚三烯并吲哚。起始原料可通过次碘酸盐催化的吲哚衍生物氧化去芳构化螺环化反应轻松制备。发现温和的碱性条件和胺的缺电子保护基对于促进化学选择性反应至关重要。此外，使用仅催化量的碳酸铯，苯胺衍生的螺吲哚啉的环扩展反应在温和得多的条件下就能顺利进行。
