Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
J Am Chem Soc. 2021 Feb 24;143(7):2920-2929. doi: 10.1021/jacs.0c13013. Epub 2021 Feb 15.
Organoboron reagents are important synthetic intermediates and have wide applications in synthetic organic chemistry. The selective borylation strategies that are currently in use largely rely on the use of transition-metal catalysts. Hence, identifying much milder conditions for transition-metal-free borylation would be highly desirable. We herein present a unified strategy for the selective C-H borylation of electron-deficient benzaldehyde derivatives using a simple metal-free approach, utilizing an imine transient directing group. The strategy covers a wide spectrum of reactions and (i) even highly sterically hindered C-H bonds can be borylated smoothly, (ii) despite the presence of other potential directing groups, the reaction selectively occurs at the -C-H bond of the benzaldehyde moiety, and (iii) natural products appended to benzaldehyde derivatives can also give the appropriate borylated products. Moreover, the efficacy of the protocol was confirmed by the fact that the reaction proceeds even in the presence of a series of external impurities.
有机硼试剂是重要的合成中间体，在有机合成化学中有广泛的应用。目前使用的选择性硼化策略主要依赖于过渡金属催化剂的使用。因此，寻找更温和的无过渡金属硼化条件是非常可取的。本文提出了一种使用简单的无金属方法，利用亚胺瞬态导向基团，对缺电子苯甲醛衍生物进行选择性 C-H 硼化的统一策略。该策略涵盖了广泛的反应范围，（i）即使是高度空间位阻的 C-H 键也能顺利地进行硼化，（ii）尽管存在其他潜在的导向基团，反应仍选择性地发生在苯甲醛部分的 -C-H 键上，（iii）苯甲醛衍生物上附加的天然产物也能得到适当的硼化产物。此外，该反应即使在存在一系列外部杂质的情况下也能进行，这一事实证实了该方案的有效性。
