Many abundant and highly bioactive natural alkaloids contain an indolizidine skeleton. A simple, high yielding method to synthesize this scaffold from N-heterocycles was developed. A wide range of pyridines, quinolines and isoquinolines reacted with donor–acceptor (DA)-aminocyclopropanes via an ytterbium(III) catalyzed [3 + 2] annulation reaction to give tetrahydroindolizine derivatives. The products were obtained with high diastereoselectivities (dr > 20:1) as anti-isomers. Additionally, the formed aminals could be easily converted into secondary and tertiary amines through iminium formation followed by reduction or nucleophile addition. This transformation constitutes the first example of dearomatization of electron-poor six-membered heterocycles via [3 + 2] annulation with DA cyclopropanes.

中文翻译：

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通过[3 + 2]与氨基环丙烷的环化反应，使电子贫乏的六元N-杂环脱芳香化

许多丰富且具有高生物活性的天然生物碱都含有吲哚并立啶骨架。开发了一种简单，高产的方法，可从N-杂环合成该支架。各种各样的吡啶，喹啉和异喹啉通过（（III）催化的[3 + 2]环化反应与供体-受体（DA）-氨基环丙烷反应，得到四氢吲哚嗪衍生物。获得的产物具有高非对映选择性（dr> 20 ：1）作为抗-异构体。另外，形成的缩醛可以通过形成亚胺，然后还原或添加亲核试剂而容易地转化为仲胺和叔胺。该转化构成了贫电子的六元杂环通过与DA环丙烷的[3 + 2]环合脱芳香化的第一个示例。