A metal-free construction of highly diastereoselective nine-membered heterocycles is described via the cycloaddition and rearrangement of N-vinyl-α,β-unsaturated ketonitrones and isocyanates. Notably, the prepared nine-membered heterocycles afforded 2,3-dihydropyrrolizines under heating conditions. Mechanistic studies showed that the nine-membered rings might undergo decarboxylation, isomerization, aza-Michael addition, and aromatization to afford 2,3-dihydropyrrolizines in a one-pot reaction.

中文翻译：

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N-乙烯基亚硝基与异氰酸酯的环加成和顺序重排合成九元杂环的非对映选择性

通过N-乙烯基-α，β-不饱和酮硝酮和异氰酸酯的环加成和重排描述了高度非对映选择性的九元杂环的无金属结构。值得注意的是，制备的九元杂环在加热条件下提供了2，3-二氢吡咯烷酮。机理研究表明，该九元环可能会通过一锅反应进行脱羧，异构化，氮杂-迈克尔加成和芳构化，从而生成2,3-二氢吡咯烷酮。