Silva María A, Pellegrinet Silvina C, Goodman Jonathan M
Department of Chemistry, University of Cambridge, Lensfield Road, UK.
J Org Chem. 2003 May 16;68(10):4059-66. doi: 10.1021/jo026821z.
This theoretical study deals with the reaction of isoprene and dichloropropynylborane. We report the results of the DFT calculations applied to the two processes involved, Diels-Alder cycloaddition and 1,4-alkynylboration. The boron influences both the chemoselectivity and the regioselectivity of this reaction through secondary orbital interactions (SOI hereafter) that give rise to transition structures with strong [4 atom + 3 atom] character. The "meta" regioselectivity observed experimentally for the reaction between 2-substituted 1,3-dienes and alkynyldihaloboranes has been explained as a result of the higher stabilization of these transition structures with "meta" orientation. Intrinsic reaction coordinate calculations were performed to determine connectivities and established the remarkable result that the geometrically very similar transition structures leading to both regioisomeric 1,4-alkynylboration products correspond to different pathways. For the "meta" orientation a direct alkynylboration of the diene through a concerted transition structure was found.
本理论研究涉及异戊二烯与二氯丙炔基硼烷的反应。我们报告了应用于所涉及的两个过程（狄尔斯-阿尔德环加成反应和1,4-炔基硼化反应）的密度泛函理论（DFT）计算结果。硼通过次级轨道相互作用（以下简称SOI）影响该反应的化学选择性和区域选择性，这种相互作用产生了具有强烈[4原子 + 3原子]特征的过渡结构。实验观察到的2-取代1,3-二烯与炔基二卤硼烷之间反应的“间位”区域选择性，已被解释为这些具有“间位”取向的过渡结构具有更高稳定性的结果。进行了内禀反应坐标计算以确定连接性，并得出了一个显著的结果，即导致两种区域异构的1,4-炔基硼化产物的几何结构非常相似的过渡结构对应于不同的反应途径。对于“间位”取向，发现二烯通过协同过渡结构直接进行炔基硼化反应。
