取代环己酮还原立体选择性的过渡态理论解释

Explanation of the Transition State Theory of the Stereoselectivity of the Reduction of Substituted Cyclohexanone

对于取代环已酮还原产物的立体选择性,仅通过还原试剂的动力学条件和生成产物的热力学稳定性进行预测是不准确的,需要考虑反应过程中存在的其他因素。采用过渡态理论可以对取代环已酮还原产物的立体选择性进行更全面、更准确的预测。一方面,还原试剂进攻羰基形成过渡态时,表现出决定立体选择性的空间位阻效应和电子效应;另一方面,反应物优势构象,即形成过渡态时的扭转应变和相对于标准对交叉构象偏转角的大小对产物的立体选择性也不容忽视。本文从过渡态形成过程中所体现的空间位阻、电子效应和构象三方面进行讨论,阐述了取代环已酮还原产物的立体选择性。

It is inaccurate to only predict the kinetic conditions of the reducing reagent and the thermodynamic stability of the resulting product during a reduction reaction.Other factors in the reaction need to be considered.Transition state theory can be used to comprehensively and accurately predict the stereoselectivity of the products formed during the reduction of substituted cyclohexanones.On the one hand,when the reducing agent attacks the carbonyl group to form a transition state,the steric hindrance and electronic effects determine the stereoselectivity of the reaction.On the other hand,the predominant conformation of the reactant,i.e.,the torsional strain when the transition state is formed and the deflection angle relative to the standard cross conformation,cannot be ignored in regard to the stereoselectivity of the product.This article discusses the steric hindrance,electronic effects,and conformation during the formation of the transition state,and explains the stereoselectivity of the reduction products formed during the reduction of substituted cyclohexanones.