Iridium‐Catalyzed Silylation of Five‐Membered Heteroarenes: High Sterically Derived Selectivity from a Pyridyl‐Imidazoline Ligand
作者:Caleb Karmel、Camille Z. Rubel、Elena V. Kharitonova、John F. Hartwig
DOI:10.1002/anie.201916015
日期:2020.4.6
The steric effects of substituents on five-membered rings are less pronounced than those on six-membered rings because of the difference in bond angles. Thus, the regioselectivities of reactions of five-membered heteroarenes that occur with selectivities dictated by steric effects, such as the borylation of C-H bonds, have been poor in many cases. We report that the silylation of five-membered-ring
由于键角不同,取代基对五元环的空间效应不如六元环上的空间效应明显。因此,在许多情况下,由空间效应决定的选择性(例如 C-H 键的硼化)发生的五元杂芳烃反应的区域选择性很差。我们报道,当由 [Ir(cod)(OMe)]2 (cod=1,5-环辛二烯) 和菲咯啉配体或新的吡啶基-咪唑啉配体的组合催化时,五元环杂芳烃的硅烷化以高空间衍生的区域选择性发生,进一步增加区域选择性。在这些催化剂的硅烷基化反应中,在这些环最空间可及的 C-H 键处官能化产生高产率的杂芳基硅烷,条件是 C-H 键与先前报道的催化剂的硼基化形成产物或不稳定的产物混合物。杂芳基硅烷产物经过交叉偶联反应和取代反应,具有 ipso 选择性,生成带有卤素、芳基和全氟烷基取代基的杂芳烃。