Exploring the Effects of Water on the Mechanism of the Catalyst-Free Reaction between Isatin and 3-Methyl-2-pyrazolin-5-one from the Mixed Implicit/Explicit Multiple Types of Water Clusters.
Exploring the Effects of Water on the Mechanism of the Catalyst-Free Reaction between Isatin and 3-Methyl-2-pyrazolin-5-one from the Mixed Implicit/Explicit Multiple Types of Water Clusters.
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DOI：
10.1021/acs.jpcb.1c08636
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发表时间：
2021-12
期刊：
影响因子：
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通讯作者：
Jianming Zhao;Xudong Liu;Yan Zhang;Ying Xue
中科院分区：
文献类型：
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作者：
Jianming Zhao;Xudong Liu;Yan Zhang;Ying Xue
采用密度泛函理论隐式/显式水分子团簇模型对靛红与3-甲基-2-吡唑啉-5-酮反应的机理和水效应进行了研究.本文提出的优先机理方案经历了三个主要步骤：首先，3-甲基-2-吡唑啉-5-酮转化为其烯醇形式，然后，靛红和烯醇之间发生羟醛加成反应生成中间体INT 2，最后INT 2发生互变异构反应成为产物3-吡唑啉酮。计算结果表明，在第二步反应中，不加水辅助的直接羟醛缩合反应是可行的，其余的互变异构步骤（步骤1、3和4）分别由三水、三水和六水簇模型辅助，是最有利的情况.进一步指出，与其他类型的水分子团簇模型相比，三水辅助反应中更多的氢键相互作用对质子转移自由能垒ΔG_m的降低是必不可少的.三水团簇模型的速率决定步骤中的更稳定的过渡态的起源归因于更小的循环应变和更多的全球电子密度转移与其结构比其他类型的水团簇模型。
Density functional theory calculations with implicit/explicit water cluster models were conducted to pursue deeper understandings about the mechanism and the water effects in the reaction of isatin with 3-methyl-2-pyrazolin-5-one. The proposed preferential mechanistic scenario here undergoes three major steps: first, 3-methyl-2-pyrazolin-5-one converts to its enol form and then, the aldol addition reaction takes place between isatin and enol to generate the intermediate INT2, followed finally by the tautomerization of INT2 to become the product 3-pyrazolone. The computed results indicate that the direct aldol reaction without the water auxiliary is feasible in the second step and the remaining tautomerization steps (steps 1, 3, and 4) assisted by tri-, tri-, and six-water cluster models, respectively, are the most favorable cases. It is further noted that more hydrogen bonding interactions in the tri-water auxiliary reaction are essential for the reduction of the free energy barrier ΔG⧧ in the proton transfer largely than those assisted by the other types of water cluster models. The origin of the more stable transition state in the rate-determining step of the tri-water cluster model is ascribed to smaller cyclic strain and more global electron density transfer associated to its structure than the other types of water cluster models.