Studies of the Mechanism and Origins of Enantioselectivity for the Chiral Phosphoric Acid-Catalyzed Stereoselective Spiroketalization Reactions
作者:Yaroslav Ya. Khomutnyk、Alonso J. Argüelles、Grace A. Winschel、Zhankui Sun、Paul M. Zimmerman、Pavel Nagorny
DOI:10.1021/jacs.5b12528
日期:2016.1.13
computational studies were conducted to elucidate the mechanism and the origins of enantiocontrol for asymmetric chiral phosphoric acid-catalyzed spiroketalization reactions. These studies were designed to differentiate between the S(N)1-like, S(N)2-like, and covalent phosphate intermediate-based mechanisms. The chiral phosphoric acid-catalyzed spiroketalization of deuterium-labeled cyclic enol ethers revealed
进行了机理和计算研究,以阐明不对称手性磷酸催化的 spiroketalization 反应的对映控制的机制和起源。这些研究旨在区分基于 S(N)1、S(N)2 和共价磷酸盐中间体的机制。氘标记的环状烯醇醚的手性磷酸催化的螺旋缩酮化显示出高度非对映选择性的顺式选择性质子化/亲核试剂加成,从而排除了长寿命的氧代碳鎓中间体。反应动力学的哈米特分析揭示了过渡态中的正电荷积累 (ρ = -2.9)。一种新的计算反应探索方法以及动力学模拟支持异步协调机制,其具有相对较短的极性过渡态(平均寿命 = 519 ± 240 fs),这与观察到的 0.85 的逆次级动力学同位素效应一致。在这些研究的基础上,提出了解释观察到的立体化学结果的过渡态模型。该模型预测观察到的产物对映异构体的对映选择性形成,具有 92% ee,与实验观察值相匹配。