Bodnar Alexandra K, Szewczyk Suzanne M, Sun Yang, Chen Yifeng, Huang Anson X, Newhouse Timothy R
Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, United States.
J Org Chem. 2024 Mar 1;89(5):3123-3132. doi: 10.1021/acs.joc.3c02572. Epub 2024 Feb 20.
Introducing degrees of unsaturation into small molecules is a central transformation in organic synthesis. A strategically useful category of this reaction type is the conversion of alkanes into alkenes for substrates with an adjacent electron-withdrawing group. An efficient strategy for this conversion has been deprotonation to form a stabilized organozinc intermediate that can be subjected to α,β-dehydrogenation through palladium or nickel catalysis. This general reactivity blueprint presents a window to uncover and understand the reactivity of Pd- and Ni-enolates. Within this context, it was determined that β-hydride elimination is slow and proceeds via concerted -elimination. One interesting finding is that β-hydride elimination can be preferred to a greater extent than C-C bond formation for Ni, more so than with Pd, which defies the generally assumed trends that β-hydride elimination is more facile with Pd than Ni. The discussion of these findings is informed by KIE experiments, DFT calculations, stoichiometric reactions, and rate studies. Additionally, this report details an in-depth analysis of a methodological manifold for practical dehydrogenation and should enable its application to challenges in organic synthesis.
在小分子中引入不饱和度是有机合成中的核心转化反应。这种反应类型中一类具有战略实用性的反应是将烷烃转化为烯烃,适用于带有相邻吸电子基团的底物。实现这种转化的一种有效策略是去质子化以形成稳定的有机锌中间体,该中间体可通过钯或镍催化进行α,β-脱氢反应。这种通用的反应性蓝图为揭示和理解钯和镍烯醇盐的反应性提供了一个窗口。在此背景下,已确定β-氢消除反应缓慢且通过协同消除进行。一个有趣的发现是,对于镍而言,β-氢消除比碳-碳键形成更占优势,比钯的情况更明显,这与通常认为的钯比镍更容易发生β-氢消除的趋势相悖。对这些发现的讨论基于动力学同位素效应(KIE)实验、密度泛函理论(DFT)计算、化学计量反应和速率研究。此外,本报告详细深入分析了一种用于实际脱氢反应的方法体系,应能使其应用于有机合成中的各种挑战。