Protodeboronation of (Hetero)Arylboronic Esters: Direct versus Prehydrolytic Pathways and Self-/Auto-Catalysis
Protodeboronation of (Hetero)Arylboronic Esters: Direct versus Prehydrolytic Pathways and Self-/Auto-Catalysis
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DOI：
10.1021/jacs.1c06863
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发表时间：
2021-08-30
影响因子：
15
通讯作者：
Lloyd-Jones, Guy C.
中科院分区：
文献类型：
--
作者：
Hayes, Hannah L. D.;Wei, Ran;Lloyd-Jones, Guy C.
用原位和停流核磁共振谱(F-19、H-1和B-11)、pH速率依赖性、同位素夹带、H-2Kie和KS-DFT计算，研究了一系列含8种不同多元醇和10个多氟芳基和杂芳基的硼酸酯的碱催化水解(ARB(OR)(2)->；ARB(OH)(2))和原脱碳反应(ARB(OR)(2)->；ARH)的动力学和机理。这项研究揭示了在基本的水-有机条件下，硼酸酯的唯象稳定性是非常微妙的。与通常的假设相反，与相应的硼酸相比，酯化不一定具有更大的稳定性。此外，当pH接近于硼酸/酯的pK(A)时，酯的水解为硼酸可以是整个原脱碳反应过程的主要组成部分，当pH接近于硼酸/酯的pK(A)时，自催化、自催化和氧化(酚醛)催化可以加强这一过程。
The kinetics and mechanism of the base-catalyzed hydrolysis (ArB(OR)(2)-> ArB(OH)(2)) and protodeboronation (ArB(OR)(2)-> ArH) of a series of boronic esters, encompassing eight different polyols and 10 polyfluoroaryl and heteroaryl moieties, have been investigated by in situ and stopped-flow NMR spectroscopy (F-19, H-1, and B-11), pH-rate dependence, isotope entrainment, H-2 KIEs, and KS-DFT computations. The study reveals the phenomenological stability of boronic esters under basic aqueous-organic conditions to be highly nuanced. In contrast to common assumption, esterification does not necessarily impart greater stability compared to the corresponding boronic acid. Moreover, hydrolysis of the ester to the boronic acid can be a dominant component of the overall protodeboronation process, augmented by self-, auto-, and oxidative (phenolic) catalysis when the pH is close to the pK(a) of the boronic acid/ester.