Ion pair dynamics: solvolyses of chiral 1,3-diarylallyl carboxylates as a case study.
Ion pair dynamics: solvolyses of chiral 1,3-diarylallyl carboxylates as a case study.
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离子对动力学：手性 1,3-二芳基烯丙基羧酸酯的溶剂分解作为案例研究
DOI：
10.1021/ja308670g
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发表时间：
2013
影响因子：
15
通讯作者：
H. Mayr
中科院分区：
文献类型：
--
作者：
K. Troshin;H. Mayr
手性离子对在现代不对称合成中起着关键作用，但人们对其性质知之甚少。我们现在已经使用的特殊功能的不对称取代烯丙基衍生物，以获得前所未有的洞察离子对动力学。通过采用手性高效液相色谱法，可以跟踪对映纯的1-（4-氯苯基）-3-苯基烯丙基和3-（4-氯苯基）-1-苯基烯丙基4-硝基苯甲酸酯水解过程中产生的所有四种异构体酯（对映异构体的两个区域异构体对）和所有四种异构体醇的时间依赖性浓度。结合这些结果与直接测量的反应速率常数的激光闪光光解产生的1-（4-氯苯基）-3-苯基烯丙基阳离子与水提供了一个完整的机理方案烯丙基羧酸溶剂分解。结果表明，溶剂分解和内部返回可以用相同的中间体来解释。用相关方程logk = sN（N + E）解释了溶剂分解反应中外部和内部返回的变量重要性。这些信息将是至关重要的飞秒激光脉冲产生的离子对的超快动力学的解释。
Chiral ion pairs play a key role in modern enantioselective synthesis, though little is known about their properties. We have now used the special features of unsymmetrically substituted allyl derivatives to obtain unprecedented insight into ion pair dynamics. By employing chiral high-performance liquid chromatography, it was possible to follow the time-dependent concentrations of all four isomeric esters (two regioisomeric pairs of enantiomers) and all four isomeric alcohols generated during the hydrolysis of enantiopure 1-(4-chlorophenyl)-3-phenylallyl and 3-(4-chlorophenyl)-1-phenylallyl 4-nitrobenzoates. Combination of these results with the directly measured rate constant for the reaction of the laser-flash photolytically generated 1-(4-chlorophenyl)-3-phenylallyl cation with water provided a complete mechanistic scheme for allyl carboxylate solvolysis. It is demonstrated that solvolysis and internal return can be explained by the same intermediates. The correlation equation logk=sN(N+E) was used to elucidate the variable importance of external and internal return in the solvolysis reactions. This information will be crucial for the interpretation of the ultrafast dynamics of ion pairs generated by femtosecond laser pulses.