The importance of four-membered NHCs in stabilizing Breslow intermediates on benzoin condensation pathway,Journal of Computational Chemistry

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The importance of four-membered NHCs in stabilizing Breslow intermediates on benzoin condensation pathway
Journal of Computational Chemistry ( IF 3.4 ) Pub Date : 2022-06-02 , DOI: 10.1002/jcc.26935
Gurudutt Dubey ₁ , Tejender Singh ₁ , Prasad V Bharatam ₁

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N-heterocyclic carbenes (NHCs) have been established to be effective organocatalysts for facilitating the benzoin condensation and many other reactions. These reactions involve the formation of a Breslow intermediate (BI), which exhibits umpolung chemistry. To facilitate organocatalysis, several new cyclic carbenes are being introduced, four-membered NHCs are of special interest. Whether these NHCs can exhibit catalytic influence or not, can be evaluated by exploring the potential energy surface (PES) of the benzoin condensation reaction. Quantum chemical analysis has been carried out to compare the PES of these four-membered NHCs with that of standard five-membered NHCs to explore their catalytic ability. The barrier for the first step of the reaction for the formation of BI is comparable in all the cases. But the barrier for the second step of the reaction leading to the benzoin formation from BI is estimated to be very high for the four membered NHCs. These results indicate that the probability of identifying and isolating the BI is very high in comparison to the completion of benzoin condensation reaction in the case of the four-membered NHCs.

中文翻译：

四元 NHC 在稳定安息香缩合途径上的 Breslow 中间体中的重要性

否-杂环卡宾 (NHC) 已被确定为促进安息香缩合和许多其他反应的有效有机催化剂。这些反应涉及 Breslow 中间体 (BI) 的形成，它表现出 umpolung 化学。为了促进有机催化，引入了几种新的环状卡宾，四元 NHC 特别令人感兴趣。这些 NHCs 是否可以表现出催化影响，可以通过探索安息香缩合反应的势能面 (PES) 来评估。已经进行了量子化学分析以将这些四元 NHC 的 PES 与标准五元 NHC 的 PES 进行比较，以探索它们的催化能力。BI 形成反应第一步的势垒在所有情况下都是可比的。但据估计，对于四元 NHC，导致 BI 形成安息香的第二步反应的势垒非常高。这些结果表明，与四元 NHC 的安息香缩合反应的完成相比，识别和分离 BI 的可能性非常高。

更新日期：2022-06-02

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