作者:Robert E. Rosenberg、W. Jonathan Kelly
DOI:10.1002/poc.3397
日期:2015.1
The understanding of the electronic effects of the diastereoselective addition of a nucleophile to a polar substituted aldehyde or ketone is not complete, with several theories competing to explain the data. For numerous hydride reductions of 3‐X‐2‐butanones (X = F, Cl, Br), the selectivity for the major syn isomer is significantly and consistently higher for X = Br than for X = F. This result is rationalized
对亲核试剂非对映选择性地加成到极性取代的醛或酮上的电子效应的理解还不完全,有几种理论相互竞争来解释这些数据。对于3-X-2-丁酮大量氢化物还原(X = F,氯,溴),对于主要的选择性顺式比为X = F。该结果合理化作为异构体显著和一贯较高对于X = Br为机制从康福思(X = F)转变为费尔金·安(Felkin–Anh)(X = Br)。通过从头算可以很好地模拟实验数据,以说明BH 3向这些酮的添加,而不是由其他亲核试剂(如LiH或LiAlH 4)进行。BH 3的能量排序过渡态主要遵循基态酮的趋势。这里,静电参数一致,将抗的C-X和CO债券的方向总是降低能量比SYN安排。的笨拙构象是在这两者之间的中间,成为能量逐渐降低,如尺寸X增加。由NBO分析判断,Felkin-Anh模型调用的超共轭相互作用仅提供有关过渡态的适度稳定。版权所有©2014 John Wiley&Sons,Ltd.