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Ring Expansion of Bicyclic Methyleneaziridines via Concerted, Near-Barrierless [2,3]-Stevens Rearrangements of Aziridinium Ylides

机译:通过协调,近禁止的双环甲基齐齐齐齐齐齐齐齐齐的环形膨胀[2,3] - 亚齐尼替代尼替代的重排

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摘要

The synthesis of densely functionalized azetidinesin a highly stereocontrolled manner is challenging, but interest in the bioactivities of these small heterocycles has stimulated methods for their preparation. We recently reported a one-carbon ring expansion of bicyclic methylene aziridines under dirhodium catalysis capable of delivering enantioenriched azetidines. This work explores this ring expansion using computational and experimental studies. DFT computations indicate that the reaction proceeds through formation of an aziridinium ylide, which is precisely poised for concerted, asynchronous ring-opening/closing to deliver the azetidines in a [2,3]-Stevens-type rearrangement. The concerted nature of this rearrangement is responsible for the stereospecificity of the reaction, where axial chirality from the initial allene substrate is transferred to the azetidine product with complete fidelity. The computed mechanistic pathway highlights the key roles of the olefin and the rigid structure of the methylene aziridine in differentiating our observed ring expansion from competing cheletropic elimination pathways noted with ylides derived from typical aziridines.
机译:浓度官能化的氮化丁胺蛋白的合成高度立体控制的方式是挑战性的,但对这些小杂环的生物活性的兴趣具有刺激其制备方法。我们最近报道了在能够递送对丙烯腈氮的催化下的双环亚甲基氮杂氨酸的单碳环膨胀。这项工作探讨了使用计算和实验研究的这种环扩展。 DFT计算表明,反应通过形成亚硝吡啶ylide的形成,该ylidinium ylide的形成,其精确地致力于齐全的异步环开/闭合,以在[2,3] - 静音型重排中输送氮化物。这种重排的齐节性质负责反应的立体特异性,其中初始苯烯基材的轴向胆度与完全保真度转移到氮乙醇产品中。计算的机械途径突出了烯烃的关键作用和亚甲基氮杂物的刚性结构在区分我们观察到的环形膨胀,从竞争来自典型的亚齐里涅替代的ylides衍生的ylides注意到。

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