Michalland Jean, Casaretto Nicolas, Zard Samir Z
Laboratoire de Synthèse Organique, CNRS UMR 7652, Ecole polytechnique, 91128, Palaiseau Cedex, France.
Laboratoire de Chimie Moleculaire, CNRS UMR 9168, Ecole polytechnique, 91128, Palaiseau Cedex, France.
Angew Chem Int Ed Engl. 2022 Jan 17;61(3):e202113333. doi: 10.1002/anie.202113333. Epub 2021 Dec 3.
A modular approach to substituted cyclobutylboronic esters is described. It proceeds by successive intermolecular radical additions of xanthates to pinacolato 1-cyclobutenylboronate and to pinacolato bicyclo[1.1.0]but-1-ylboronate. Success hinges on tuning the stability of the α-boryl radical by exploiting the stabilizing influence of the trivalent boronic ester and the slightly destabilizing cyclobutane, which increases the σ-character of the radical. Reductive removal of the xanthate group finally provides a range of 1,2- and 1,3-disubstituted cyclobutylboronic esters. The contrast with cyclopropylboronic esters is striking, since the strong destabilization by the highly strained cyclopropane ring allows the first radical addition to take place but not the second. Furthermore, the first adducts are geminal xanthyl boronic esters that can be converted into cyclobutanones. This chemistry furnishes cyclobutylboronic esters that would be quite difficult to obtain otherwise and thus complements existing methods.
本文描述了一种用于合成取代环丁基硼酸酯的模块化方法。该方法通过黄原酸酯分子间依次对频哪醇1-环丁烯基硼酸酯和频哪醇双环[1.1.0]丁-1-基硼酸酯进行自由基加成来实现。成功的关键在于利用三价硼酸酯的稳定作用和环丁烷的轻微去稳定作用来调节α-硼自由基的稳定性，这种作用增加了自由基的σ-特性。黄原酸酯基团的还原消除最终提供了一系列1,2-和1,3-二取代的环丁基硼酸酯。与环丙基硼酸酯形成鲜明对比的是，高度张力的环丙烷环导致的强烈去稳定作用使得第一个自由基加成能够发生，但第二个不能。此外，第一个加合物是偕二黄原酸硼酸酯，可以转化为环丁酮。这种化学方法提供了用其他方法很难获得的环丁基硼酸酯，从而补充了现有方法。
