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Ring Expansion of Bicyclic Methyleneaziridines via Concerted, Near-Barrierless [2,3]-Stevens Rearrangements of Aziridinium Ylides
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-07-17 00:00:00 , DOI: 10.1021/acscatal.8b02206 Steven C Schmid 1 , Ilia A Guzei 1 , Israel Fernández 2 , Jennifer M Schomaker 1
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-07-17 00:00:00 , DOI: 10.1021/acscatal.8b02206 Steven C Schmid 1 , Ilia A Guzei 1 , Israel Fernández 2 , Jennifer M Schomaker 1
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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.
中文翻译：
通过氮丙啶叶立德的协同、近无障碍 [2,3]-Stevens 重排实现双环亚甲基氮丙啶的扩环
以高度立体控制的方式合成密集官能化的氮杂环丁烷具有挑战性，但对这些小杂环的生物活性的兴趣刺激了它们的制备方法。我们最近报道了双环亚甲基氮丙啶在二铑催化下的一碳环扩展，能够提供对映体富集的氮杂环丁烷。这项工作通过计算和实验研究探索了这种环扩展。 DFT 计算表明，该反应通过形成氮丙啶叶立德进行，该叶立德精确地准备好协调、异步开环/闭环，以 [2,3]-Stevens 型重排传递氮杂环丁烷。这种重排的协同性质决定了反应的立体特异性，其中来自初始丙二烯底物的轴向手性以完全保真度转移到氮杂环丁烷产物。计算的机理途径强调了烯烃和亚甲基氮丙啶的刚性结构在区分我们观察到的环扩张与源自典型氮丙啶的叶立德的竞争性螯合消除途径中的关键作用。
更新日期：2018-07-17
中文翻译：
通过氮丙啶叶立德的协同、近无障碍 [2,3]-Stevens 重排实现双环亚甲基氮丙啶的扩环
以高度立体控制的方式合成密集官能化的氮杂环丁烷具有挑战性，但对这些小杂环的生物活性的兴趣刺激了它们的制备方法。我们最近报道了双环亚甲基氮丙啶在二铑催化下的一碳环扩展，能够提供对映体富集的氮杂环丁烷。这项工作通过计算和实验研究探索了这种环扩展。 DFT 计算表明，该反应通过形成氮丙啶叶立德进行，该叶立德精确地准备好协调、异步开环/闭环，以 [2,3]-Stevens 型重排传递氮杂环丁烷。这种重排的协同性质决定了反应的立体特异性，其中来自初始丙二烯底物的轴向手性以完全保真度转移到氮杂环丁烷产物。计算的机理途径强调了烯烃和亚甲基氮丙啶的刚性结构在区分我们观察到的环扩张与源自典型氮丙啶的叶立德的竞争性螯合消除途径中的关键作用。
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