协同亲核取代,称为 S N 2 反应,是合成中用于引入新官能团并构建碳-碳和碳-杂原子键1 的基本有机转化。 S N 2 反应通常涉及亲核试剂对C( sp 3 )−X 键(X=卤素或其他离去基团)的σ* 轨道的背面攻击,导致立体中心2的完全反转。相比之下,电子无偏sp 2乙烯基亲电子试剂上相应的立体反转亲核取代,即协同 S N V(σ) 反应,要罕见得多,并且到目前为止,仅限于精心设计的底物,主要发生在成环过程中3,4 。在这里,我们表明,金属化配合物中提出的应变释放机制可以加速协同的 S N V 反应,从而导致多种有机硼酸酯的通用和立体特异性亚烯基同系物的发展。该方法能够迭代并入多个亚烯基单元,从而产生以其他方式难以制备的交叉共轭多烯。还证明了其在含有多取代烯烃的生物活性化合物的合成中的进一步应用。计算研究表明,方形平面过渡态中空间应变的减少促进了一种不寻常的 S N 2 样协同途径,这解释了这种金属化物
Iron-Based Catalyst for Borylation of Unactivated Alkyl Halides without Using Highly Basic Organometallic Reagents
作者:Sheema Siddiqui、Ramesh Bhawar、K. Geetharani
DOI:10.1021/acs.joc.0c02364
日期:2021.1.15
alkyl bromides and chlorides with bis(neopentylglycolato)diborane (B2neop2) mediated by iron-bis amide is described. The reaction proceeds with a broad substrate scope and good functional group compatibility. Moreover, sufficient catalytic activity was obtained for primary and secondary alkyl halides. Mechanistic studies indicate that the reaction proceeds through a radical pathway.
Efficient Hydrolysis of Organotrifluoroborates via Silica Gel and Water
作者:Gary A. Molander、Livia N. Cavalcanti、Belgin Canturk、Po-Shen Pan、Lauren E. Kennedy
DOI:10.1021/jo901441u
日期:2009.10.2
and efficient method for the hydrolysis of organotrifluoroborates to unveil boronic acids using silicagel and H2O was developed. This method proved to be tolerant of a broad range of aryl-, heteroaryl-, alkenyl-, and alkyltrifluoroborates as well as structurally diverse aminomethylated organotrifluoroborates. As anticipated, electron-rich substrates provided the corresponding boronic acids more readily
开发了一种使用硅胶和 H 2 O水解有机三氟硼酸盐以揭示硼酸的通用、温和且有效的方法。事实证明,该方法可以耐受各种芳基-、杂芳基-、烯基-和烷基三氟硼酸盐以及结构多样的氨甲基化有机三氟硼酸盐。正如预期的那样,由于共振稳定的二氟硼烷中间体,富电子底物比缺电子底物更容易提供相应的硼酸。开发的方法进一步扩展用于将有机三氟硼酸盐转化为相应的硼酸酯。
Iterative Synthesis of Alkenes by Insertion of Lithiated Epoxides into Boronic Esters
The insertion of lithiated epoxides into boronic esters followed by thermal syn-elimination provides a stereospecific entry to alkenes. This process avoids transition metals and is amenable to iteration to provide higher substitution patterns.
cobalt-complex-catalyzed borylation of a wide range of alkyl halides with a diboron reagent (B2pin2 or B2neop2) has been developed under mild reaction conditions, demonstrating the first cobalt-mediated cross-coupling with alkyl electrophiles. This protocol allows alkyl boronic esters to be accessed from alkyl halides, including alkylchlorides, which were used rarely as coupling partners. Mechanistic