英国布里斯托大学Varinder Kumar Aggarwal团队对邻环烷基2,4,6-三异丙基苯甲酸酯的锂化、硼化和1,2-金属酸盐重排反应进行了研究。相关研究成果发表在2021年3月2日出版的《德国应用化学》。

在锂化-硼酰化反应中使用了大量的无环一级和二级2,4,6-三异丙基苯甲酸酯（TIB），但环状TIB酯没有。该文研究了环TIB酯在锂化-硼化反应中的应用，并研究了环尺寸（3→6元环）对锂化-硼化方案的三个关键步骤的影响：去质子化、硼化和1,2-金属酸盐重排。

虽然所有尺寸的环都可以脱质子，但环己基的反应速度非常慢，环戊基的α -消去速度在78°C下比脱质子更快，因此不能使用。环丁基和环丙基都经历了快速硼化，但只有环丁基底物经历了1,2-金属酸盐重排。因此，环丁基TIB酯占据了一个“Goldilocks区”，小到足以脱质子，大到足以使1,2迁移。使用广泛的硼酸酯对反应的一般性进行了探索。

附：英文原文

Title: Studies on the lithiation, borylation, and 1,2‐metalate rearrangement of O‐cycloalkyl 2,4,6‐triisopropylbenzoates

Author: Varinder Kumar Aggarwal, Pradip Songara, Eugenia Luc, Jack Rogers, Ellie Stammers, Rory Mykura

Issue&Volume: 2021-03-02

Abstract: A broad range of acyclic primary and secondary 2,4,6‐triisopropylbenzoate (TIB) esters have been used in lithiation‐borylation reactions, but cyclic TIB esters have not. We have studied the use of cyclic TIB esters in lithiation‐borylation reactions and looked at the effect of ring size (3 → 6‐membered rings) on the three key steps of the lithiation–borylation protocol: deprotonation, borylation and 1,2‐metalate rearrangement. While all rings sizes could be deprotonated, the cyclohexyl case was impractically slow, and the cyclopentyl example underwent α‐elimination faster than deprotonation at 78 °C and so could not be used. Both cyclobutyl and cyclopropyl cases underwent rapid borylation, but only the cyclobutyl substrate underwent 1,2‐metalate rearrangement. Thus, the cyclobutyl TIB ester occupies a “Goldilocks zone,” being small enough for deprotonation and large enough to enable 1,2‐migration. The generality of the reaction was explored with a broad range of boronic esters.

DOI: 10.1002/anie.202101374

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202101374