Stability of boronic esters – Structural effects on the relative rates of transesterification of 2-(phenyl)-1,3,2-dioxaborolane
作者:Chandra D. Roy、Herbert C. Brown
DOI:10.1016/j.jorganchem.2006.10.013
日期:2007.1
phenylboronic ester 2-(phenyl)-1,3,2-dioxaborolane with a wide variety of structurally modified diols, have been studied to understand the factors influencing the relative stabilities of boronic esters. It is found that the alkyl substituents on the α-carbons of diols slow down the transesterification, but produce thermodynamically more stable boronic ester. Six-membered boronic esters are thermodynamically
已研究了非手性环状苯基硼酸酯2-(苯基)-1,3,2-二氧杂硼烷与各种结构改性的二醇的相对反应速率,以了解影响硼酸酯相对稳定性的因素。发现二醇的α-碳上的烷基取代基减慢了酯交换反应,但是产生了热力学上更稳定的硼酸酯。六元硼酸酯在热力学上比其相应的五元类似物稳定。在环状1,2-二醇中,顺式-1,2-环戊二醇可瞬间取代乙二醇,而反式-1,2-环戊二醇则完全不活泼,这表明顺式1,2-二醇的-立体化学是酯交换的先决条件。在1,5-二醇中,二乙醇胺相当快地取代了乙二醇,形成了更稳定的双环螯合物,其中氮通过配位键连接到硼上(如11 B NMR光谱所证明的)。二(乙二醇)的氧原子和2,2'-硫代二乙醇的硫原子无助于从其硼酸酯中置换乙二醇。