Investigation of the Electronic Origin of Asymmetric Induction in Palladium-Catalyzed Allylic Substitutions with Phosphinooxazoline (PHOX) Ligands by Hammett and Swain–Lupton Analysis of the <sup>13</sup>C NMR Chemical Shifts of the (π-Allyl)palladium Intermediates
作者:Paul B. Armstrong、Elizabeth A. Dembicer、Andrew J. DesBois、Jay T. Fitzgerald、Janet K. Gehrmann、Nathaniel C. Nelson、Amelia L. Noble、Richard C. Bunt
DOI:10.1021/om3007163
日期:2012.10.8
typically obtained with PHOX ligands exceeds the approximately 8/1 ratio of exo to endo intermediates. Swain–Lupton analysis reveals the importance of both resonance and field effects by the substituents regardless of their location and supports the overall electronic control model for enantioselection by PHOX ligands. For rational chiral ligand design and electronic tuning of ligand properties, these results
同构的4'-和5'-取代的膦基恶唑啉(PHOX)配体用于探测对(1,3-二苯基烯丙基)钯PHOX配体络合物的对映选择性亲核加成的电子来源。Hammett分析烯丙基C-1和C-3碳的13 C NMR化学位移表明,主要的外型非对映异构体较不易受C-1和C-3处的差异变化的影响,并且取代基的位置较小对这些变化的影响。相反,次要的内非对映异构体更容易受到差异13的影响在C-1和C-3处的C NMR变化以及取代基的位置对这些变化影响更大。内非对映异构体通过横跨钯中心的氮和磷原子的连接显示出显着的“顺式作用”,这解释了其较低的反应性,因此,通常用PHOX配体获得的对映选择性如何超过外切与内切中间体的约8/1比例。Swain-Lupton分析揭示了无论取代基的位置如何,共振和场效应的重要性,并支持了PHOX配体对映异构的整体电子控制模型。为了进行合理的手性配体设计和电子调节配体性质,