A directive Ni catalyst overrides conventional site selectivity in pyridine C–H alkenylation
作者:Tao Zhang、Yu-Xin Luan、Nelson Y. S. Lam、Jiang-Fei Li、Yue Li、Mengchun Ye、Jin-Quan Yu
DOI:10.1038/s41557-021-00792-1
日期:2021.12
Achieving the transition metal-catalysed pyridine C3âH alkenylation, with pyridine as the limiting reagent, has remained a long-standing challenge. Previously, we disclosed that the use of strong coordinating bidentate ligands can overcome catalyst deactivation and provide Pd-catalysed C3 alkenylation of pyridines. However, this strategy proved ineffective when using pyridine as the limiting reagent, as it required large excesses and high concentrations to achieve reasonable yields, which rendered it inapplicable to complex pyridines prevalent in bioactive molecules. Here we report that a bifunctional N-heterocyclic carbene-ligated NiâAl catalyst can smoothly furnish C3âH alkenylation of pyridines. This method overrides the intrinsic C2 and/or C4 selectivity, and provides a series of C3-alkenylated pyridines in 43â99% yields and up to 98:2 C3 selectivity. This method not only allows a variety of pyridine and heteroarene substrates to be used as the limiting reagent, but is also effective for the late-stage C3 alkenylation of diverse complex pyridine motifs in bioactive molecules. Selective CâH alkenylation of pyridines at the C3 position, with the pyridine as the limiting reagent, is a long-standing synthetic challenge. Now, it has been shown that this can be achieved using a bifunctional N-heterocyclic carbene-ligated NiâAl catalyst that overrides the intrinsic C2/4 selectivity of pyridines and enables the selective late-stage functionalization of a range of complex pyridyl-containing motifs.
实现以吡啶为限制试剂的过渡金属催化的吡啶C3-H烯基化一直是一个长期挑战。此前,我们披露使用强配位的双齿配体可以克服催化剂的失活,并提供Pd催化的吡啶C3烯基化。然而,当使用吡啶作为限制试剂时,这一策略效果不佳,因为它需要大量的过量和高浓度才能获得合理的产率,这使其无法应用于生物活性分子中常见的复杂吡啶。现在,我们报告一种双功能N-杂环卡宾配位的Ni-Al催化剂能够顺利实现吡啶的C3-H烯基化。这种方法克服了吡啶固有的C2和/或C4选择性,提供了一系列C3-烯基化吡啶,产率在43-99%之间,C3选择性高达98:2。这种方法不仅允许多种吡啶和杂环芳烃底物作为限制试剂使用,而且在生物活性分子中对多种复杂吡啶基团的后期C3烯基化也有效。选择性在C3位置对吡啶进行C-H烯基化,以吡啶为限制试剂,是一个长期的合成挑战。现在显示,这可以通过一种双功能N-杂环卡宾配位的Ni-Al催化剂实现,该催化剂克服了吡啶的固有C2/4选择性,并使得多种复杂吡啶基团的后期选择性功能化成为可能。