Preassociation, Free-Ion, and Ion-Pair Pathways in the Electrophilic Bromination of Substituted cis- and trans-Stilbenes in Protic Solvents
Preassociation, Free-Ion, and Ion-Pair Pathways in the Electrophilic Bromination of Substituted cis- and trans-Stilbenes in Protic Solvents
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质子溶剂中取代的顺式和反式二苯乙烯亲电溴化中的预缔合、自由离子和离子对途径
DOI：
10.1021/ja9700461
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发表时间：
1997
影响因子：
15
通讯作者：
G. Bellucci
中科院分区：
文献类型：
--
作者：
M. Ruasse;G. Moro;B. Galland;R. Bianchini;‡. A. Cinzia Chiappe;G. Bellucci
在乙酸、三氟乙醇、乙醇、甲醇和水-甲醇混合物中研究了环取代的顺式和反式芪的亲电溴化反应速率和产物。mYBr关系（仅对亲核溶剂呈线性，m = 0.8），两种非亲核溶剂与mYBr曲线的偏差（ΔAcOH和ΔTFE为正、负或可忽略），动力学溶剂同位素效应（kMeOH/kMeOD = 1.1−1.6），化学选择性（主要是二溴化物，DB，或溶剂结合的加合物，MA），以及立体化学对溶剂和取代基的高度依赖性（从立体会聚立体特异性）进行了讨论和解释的机制计划，类似于詹克斯计划的脂肪族亲核取代，其中preassociation，自由离子和离子对途径竞争。特别是，这些反应的立体化学结果是一致的显着变化的亲核合作伙伴的产品-f…
Rates and products of electrophilic bromination of ring-substituted cis- and trans-stilbenes have been investigated in acetic acid, trifluoroethanol, ethanol, methanol, and water−methanol mixtures. The mYBr relationships (linear for nucleophilic solvents only, with m = 0.8), the deviations of the two nonnucleophilic solvents from the mYBr plots (ΔAcOH and ΔTFE positive, negative, or negligible), the kinetic solvent isotope effects (kMeOH/kMeOD = 1.1−1.6), the chemoselectivity (predominant dibromide, DB, or solvent-incorporated adducts, MA), and the high dependence of the stereochemistry on the solvent and the substituents (from stereoconvergency to stereospecificity) are discussed and interpreted in terms of a mechanistic scheme, analogous to the Jencks scheme for aliphatic nucleophilic substitutions, in which preassociation, free-ion, and ion-pair pathways compete. In particular, the stereochemical outcome of these reactions is consistent with a marked change in the nucleophilic partners of the product-f...