Palladium(II)/Lewis Acid-Catalyzed Oxidative Olefination/Annulation of N-Methoxybenzamides: Identifying the Active Intermediates through NMR Characterizations.,The Journal of Organic Chemistry

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Palladium(II)/Lewis Acid-Catalyzed Oxidative Olefination/Annulation of N-Methoxybenzamides: Identifying the Active Intermediates through NMR Characterizations.
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2020-06-26 , DOI: 10.1021/acs.joc.9b03484
Jing-Wen Xue ₁ , Miao Zeng ₁ , Hongwu Jiang ₁ , Kaiwen Li ₁ , Zhuqi Chen ₁ , Guochuan Yin ₁

Affiliation

Although Pd(II)-catalyzed C–H activation in arenes has been widely successful in organic synthesis with many palladacycle compounds isolated as the intermediates in ligand-directed C–H activation, direct identification of the reaction intermediates such as the π-complex prior to the C–H activation is still not successful because of their instability. In the present study, we introduce a Pd(II)/LA (LA: Lewis acid)-catalyzed oxidative olefination/annulation reaction between N-methoxybenzamides and acrylates with oxygen as the oxidant source, in which two intermediates, including an unsymmetrical η⁶-complex and a palladacycle species without the proton releasing to the environment, were identified through NMR characterizations. The in situ formation of the heterobimetallic Pd(II)/LA species such as Pd(II)/Sc(III) may have enhanced the electrophilic properties of the Pd²⁺ cation, thus improving the stability of the π-complex, herein, an unsymmetrical η⁶-complex, and improving its catalytic efficiency. The observed insensitive electronic effect preferred the concerted metalation–deprotonation (CMD) mechanism for this C–H activation, and the detected palladacycle intermediate without the proton releasing to the environment offered an experimental clue to support the proposed CMD mechanism.

中文翻译：

钯（II）/路易斯酸催化的氧化烯烃氧化/ N-甲氧基苯甲酰胺环化：通过NMR表征鉴定活性中间体。

尽管Pd（II）催化的芳烃中的C–H活化在有机合成中已经取得了广泛的成功，并且分离了许多Palladacycle化合物作为配体导向的C–H活化的中间体，但是可以直接鉴定反应中间体，例如π-络合物由于不稳定，C–H激活仍然无法成功。在本研究中，我们引入一个钯（II）/ LA（LA：路易斯酸）催化氧化烯/环之间的反应Ñ -methoxybenzamides和丙烯酸酯与氧作为氧化剂源，其中两个中间体，包括不对称的η ⁶通过NMR鉴定，确定了复合物和没有质子释放到环境中的palladacycle物种。在原位诸如Pd（II）/ Sc（III）的杂双金属Pd（II）/ LA物种的形成可能会增强Pd ²⁺阳离子的亲电特性，从而改善π络合物的稳定性，此处为不对称η ^6-络合物，并提高其催化效率。观察到的不灵敏的电子效应更倾向于协同金属化-去质子化（CMD）机理来实现这种C-H活化，并且检测到的不存在质子释放到环境中的palladacycle中间体提供了支持该CMD机理的实验线索。

更新日期：2020-07-17

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