Li Yin, Fan Wen-Xin, Luo Shuang, Trofimova Alina, Liu Yuan, Xue Jiang-Hao, Yang Ling, Li Qingjiang, Wang Honggen, Yudin Andrei K
Guangdong Key Laboratory of Chiral Molecule and Drug Discovery, School of Pharmaceutical Sciences, Sun Yat-Sen University, Guangzhou 510006, China.
State Key Laboratory of Respiratory Disease, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, 190 Kaiyuan Avenue, Guangzhou 510530, China.
J Am Chem Soc. 2023 Apr 5;145(13):7548-7558. doi: 10.1021/jacs.3c00860. Epub 2023 Mar 22.
Electrophilic addition to alkenes is a textbook-taught reaction, yet it is not always possible to control the regioselectivity of addition to unsymmetrical 1,2-disubstituted substrates. We report the observation and applications of the β-boron effect that accounts for high regioselectivity in electrophilic addition reactions to allylic MIDA (-methyliminodiacetic acid) boronates. While the well-established β-silicon effect bears partial resemblance to the observed reactivity, the silyl group is typically lost during functionalization. In contrast, the boryl moiety is retained in the product when B(MIDA) is used as the nucleophilic stabilizer. Mechanistic studies elucidate the origin of this effect and demonstrate how σ(C-B) hyperconjugation helps stabilize the incipient carbocation. This transformation represents a rare example of the stereospecific hydrohalogenation of secondary allyl MIDA-boronates that proceeds in a syn-fashion.
烯烃的亲电加成是教科书上讲授的反应，但对于不对称的1,2 - 二取代底物，控制加成的区域选择性并不总是可行的。我们报道了β - 硼效应的观察结果及其应用，该效应解释了亲电加成反应中烯丙基MIDA（-甲基亚氨基二乙酸）硼酸酯具有高区域选择性的原因。虽然已确立的β - 硅效应与观察到的反应活性有部分相似之处，但硅基在官能化过程中通常会失去。相比之下，当使用B（MIDA）作为亲核稳定剂时，硼基部分会保留在产物中。机理研究阐明了这种效应的起源，并证明了σ（C - B）超共轭如何有助于稳定初始碳正离子。这种转化代表了仲烯丙基MIDA - 硼酸酯以顺式进行的立体选择性氢卤化的罕见例子。
