Institut für Organische Chemie und Makromolekulare Chemie, Friedrich-Schiller-Universität Jena, Humboldtstr. 10, 07743, Jena, Germany.
Institut für Elektrochemie, Universität Ulm, Albert-Einstein-Allee 47, 89081, Ulm, Germany.
Chemistry. 2020 Jul 14;26(39):8639-8650. doi: 10.1002/chem.202001479. Epub 2020 Jun 22.
Allylboration reactions rank among the most reliable tools in organic synthesis. Herein, we report a general synthesis of trifunctionalized allylboronates and systematic investigations of their stereocontrolled transformations with substituted aldehyde substrates, in order to efficiently access diverse, highly substituted target substrates. A peculiar transition in stereocontrol was observed from the polar Felkin-Anh (PFA) to the Cornforth-Evans (CE) model for alkoxy- and epoxy-substituted aldehydes. CE-type transition states were uniformly identified as minima in advanced, DFT-based computational studies of allylboration reactions of epoxy aldehydes, conforming well to the experimental data, and highlighting the underestimated relevance of this model. Furthermore, a mechanism-based rationale for the substitution pattern of the epoxide was delineated that ensures high levels of stereocontrol and renders α,β-epoxy aldehydes generally applicable substrates for target synthesis.
烯丙基硼酸酯反应是有机合成中最可靠的工具之一。在此，我们报告了三官能化烯丙基硼酸酯的一般合成方法，并对其与取代醛底物的立体控制转化进行了系统研究，以有效地获得不同的、高取代的目标底物。对于烷氧基和环氧化物取代的醛，观察到立体控制从极性费尔肯-安（PFA）到康福斯-埃文斯（CE）模型的特殊转变。在对环氧醛的烯丙基硼化反应进行的先进的基于 DFT 的计算研究中，CE 型过渡态被一致地确定为最小值，与实验数据吻合良好，突出了该模型的被低估的相关性。此外，还阐述了环氧化物取代模式的基于机制的基本原理，该原理确保了高水平的立体控制，并使α，β-环氧醛成为目标合成的一般适用底物。
