Diastereoselectivity of Enolate Anion Protonation. H/D Exchange of β-Substituted Ethyl Butanoates in Ethanol-<i>d</i>
作者:Jerry R. Mohrig、Robert E. Rosenberg、John W. Apostol、Mark Bastienaansen、Jordan W. Evans、Sonya J. Franklin、C. Daniel Frisbie、Sabrina S. Fu、Michelle L. Hamm、Christopher B. Hirose、David A. Hunstad、Thomas L. James、Randall W. King、Christopher J. Larson、Hallie A. Latham、David A. Owen、Karin A. Stein、Ronald Warnet
DOI:10.1021/ja962631s
日期:1997.1.1
The stereochemistry of base-catalyzed H/D exchange on 13 β-substituted ethyl butanoates in ethanol-d has been studied in order to analyze the steric and electronic factors which control the diastereoselectivity of electrophilic attack on enolate anions. Electrophilic deuteration of the enolate anion also determines the stereoselectivity of 1,4-conjugate addition of ethanol-d to α,β-unsaturated esters
研究了乙醇-d 中 13 β-取代丁酸乙酯的碱催化 H/D 交换的立体化学,以分析控制亲电攻击烯醇阴离子的非对映选择性的空间和电子因素。烯醇阴离子的亲电氘化也决定了 1,4-共轭加成乙醇-d 到 α,β-不饱和酯的立体选择性。选择严格排除离子配对和聚集影响的实验条件。研究表明,立体电子因素通常比立体效应产生更高的立体选择。C-3 处带负电的杂原子取代基产生 10:1 的 2R*,3R*/2R*,3S*2-氘代丁酸酯。在最稳定的亲电攻击过渡态中,这些带负电的取代基占据形成 C-D 键的反面位置。只有用 β-叔丁基取代基才能产生高立体选择性,并且它随着递减速度的降低而迅速下降。