Vorozhtsov Novosibirsk Institute of Organic Chemistry, Pr. Lavrentieva 9, Novosibirsk, 630090, Russia.
Boreskov Institute of Catalysis, Pr. Lavrentieva 5, Novosibirsk, 630090, Russia.
Org Biomol Chem. 2022 Aug 31;20(34):6799-6808. doi: 10.1039/d2ob01141g.
Superelectrophilic activation of α,β-unsaturated carbonyl compounds and their isoelectronic analogs, proceeding normally under superacidic conditions, have led to a great variety of beneficial synthetic transformations. However, the essence of such activation is not yet fully recognized, while a number of alternative views on the subject have been discussed at length in the literature. Here, taking the example of virtual reactions of cinnamonitrile and benzalacetone with benzene, their feasible mechanistic variants, including multiple protonation (coordination to AlCl) of the reactants, were analyzed based on density functional theory (DFT). It is revealed that the most plausible reaction pathways involve the initial - or -protonation (coordination to AlCl) of the activated compounds followed by subsequent protonation on the α-C-atom. Dicationic superelectrophiles thus formed ensure practically barrier-free reactions with benzene in addition to a more favorable energetic profile of their generating, which is in marked contrast to other potential reaction pathways.
超亲电活化的α，β-不饱和羰基化合物及其等电子类似物，在超强酸条件下通常可以进行，这导致了各种各样有益的合成转化。然而，这种活化的本质尚未被完全认识，同时，文献中也对该主题进行了长时间的讨论，提出了一些替代观点。在这里，以肉桂腈和苯甲醛与苯的虚拟反应为例，基于密度泛函理论（DFT）分析了它们可能的机理变体，包括反应物的多次质子化（与 AlCl 配位）。结果表明，最可能的反应途径涉及活化化合物的初始 - 或 - 质子化（与 AlCl 配位），随后在α-C 原子上进一步质子化。形成的二价超亲电试剂不仅与苯发生无势垒反应，而且其生成的能量分布也更有利，这与其他潜在的反应途径形成鲜明对比。
