Base-Catalyzed Aryl-B(OH)<sub>2</sub> Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion
作者:Paul A. Cox、Marc Reid、Andrew G. Leach、Andrew D. Campbell、Edward J. King、Guy C. Lloyd-Jones
DOI:10.1021/jacs.7b07444
日期:2017.9.20
Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (Ka) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the
Kuivila于50年前发表的开创性研究表明,硼酸酯的ipso质子化是芳基硼酸的碱催化原脱硼硼烷的机理。但是,该研究仅限于酸性条件下的紫外分光光度法分析,并且估计了水的缔合常数(K a)。借助于NMR,停止流IR和骤冷流技术,现在已经在70°C的二恶烷水溶液中,在pH> 13的条件下,测定了30种不同的芳基硼酸的碱催化原硼酸脱氢反应的动力学。研究中包括C 6 H n F (5- n) B(OH)2的所有20个异构体半衰期跨越9个数量级:<3毫秒至6.5个月。在具有pH率分布,对组合ķ一个和Δ小号⧧值,动力学同位素效应(2 H,10 B,13 C),线性自由能的关系,并密度泛函理论计算,我们已经确定,涉及一种机械制度硼酸酯的单分子杂化与协同的ipso质子化/ C–B裂解竞争。芳基硼酸的相对路易斯酸度与它们的原脱硼氢硼酸速度不相关,特别是当存在邻位取代基时。值得注意的是,3,5-二硝基苯基硼酸