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A mechanistic study on the regioselective Ni-catalyzed methylation–alkenylation of alkyne with AlMe3 and allylic alcohol
Organic Chemistry Frontiers ( IF 5.4 ) Pub Date : 2021-11-17 , DOI: 10.1039/d1qo01580j
Jiao Liu 1 , Deguang Liu 1 , Wan Nie 1 , Haizhu Yu 2 , Jing Shi 1
Affiliation  

The recently reported Ni-catalyzed methylation–allylation of alkynes with allylic alcohols and AlMe3 reagents delivers valuable tetrasubstituted alkene units in a highly regioselective fashion. Motivated by the experimental significance and the mechanistic ambiguity (e.g. the details of C–O bond activation, the function of the Lewis acid AlMe3, etc.), we conducted a detailed mechanistic study using density functional theory (DFT) calculations. The reaction was found to occur via the C–O bond activation of allylic alcohol, allylation of alkyne, transmetalation, reductive elimination and catalyst regeneration steps. AlMe3 could easily react with the allylic alcohol to form a cyclodialuminoxane species bearing two groups of Lewis acid–base interactions. In this regard, the C(allyl)–O bond is remarkably activated, resulting in a relatively facile C–O activation (compared to the typical Lewis-acid mediated reactions). In addition, the Al–Me interaction is a double-edged sword to the methylation step: the cyclodialuminoxane group functions as the methyl resource, while the full dissociation of the Al–Me interaction (via a cis-to-trans isomerization) is a requisite to fully release the methyl group. In this context, the “Me-relay” pathway involving the [Ni]–Me intermediate is found to be more plausible than all other mechanistic possibilities (such as the typical concerted Me-transfer mechanism in previous studies).

中文翻译:

AlMe3和烯丙醇区域选择性Ni催化炔烃甲基化-烯基化的机理研究

最近报道的镍催化炔烃与烯丙醇和 AlMe 3试剂的甲基化烯丙基化以高度区域选择性的方式提供有价值的四取代烯烃单元。通过实验意义和机械歧义(动机例如C-O键活化,路易斯酸阿尔梅的功能的细节3等等。),我们进行了使用密度泛函理论(DFT)计算的详细机理研究。发现该反应是通过烯丙醇的 C-O 键活化、炔烃的烯丙基化、金属转移、还原消除和催化剂再生步骤发生的。阿尔梅3可以很容易地与烯丙醇反应形成带有两组路易斯酸碱相互作用的环二铝氧烷物质。在这方面,C(烯丙基)-O 键被显着激活,导致相对容易的 C-O 激活(与典型的路易斯酸介导的反应相比)。此外,将Al-ME相互作用是双刃剑到甲基化步骤:在cyclodialuminoxane组用作甲基资源,而在Al-ME相互作用的完整的解离(经由一个顺式-到-反式异构化)是完全释放甲基的必要条件。在这种情况下,发现涉及 [Ni]-Me 中间体的“Me-relay”途径比所有其他机械可能性(例如以前研究中典型的协调 Me-转移机制)更合理。
更新日期:2021-12-01
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