Fordham James M, Grayson Matthew N, Aggarwal Varinder K
School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.
Angew Chem Int Ed Engl. 2019 Oct 21;58(43):15268-15272. doi: 10.1002/anie.201907617. Epub 2019 Sep 18.
Alkenyl boronic esters are important reagents in organic synthesis. Herein, we report that these valuable products can be accessed by the homologation of boronic esters with lithiated epoxysilanes. Aliphatic and electron-rich aromatic boronic esters provided vinylidene boronic esters in moderate to high yields, while electron-deficient aromatic and vinyl boronic esters were found to give the corresponding vinyl silane products. Through DFT calculations, this divergence in mechanistic pathway has been rationalized by considering the stabilization of negative charge in the C-Si and C-B bond breaking transition states. This vinylidene homologation was used in a short six-step stereoselective synthesis of the proposed structure of machillene, however, synthetic and reported data were found to be inconsistent.
烯基硼酸酯是有机合成中的重要试剂。在此，我们报道这些有价值的产物可通过硼酸酯与锂化环氧硅烷的同系化反应得到。脂肪族和富电子芳香族硼酸酯能以中等至高产率提供亚乙烯基硼酸酯，而缺电子芳香族硼酸酯和乙烯基硼酸酯则生成相应的乙烯基硅烷产物。通过密度泛函理论计算，考虑到C-Si和C-B键断裂过渡态中负电荷的稳定作用，这种机理途径的差异得到了合理的解释。这种亚乙烯基同系化反应被用于马奇林（machillene）假定结构的简短六步立体选择性合成中，然而，发现合成数据与报道的数据不一致。
