Despite numerous efforts, the synthesis of scalemic carbo‐ and heterocycles through Pd⁰‐catalyzed C(sp³)−H activation employing chiral ancillary ligands or chiral bases is still limited. Inspired by the recently reported outstanding performance of IBiox‐type NHC ligands and bifunctional ligands in similar transformations, a new class of bifunctional NHC‐ligands bearing a pendant carboxylate group was designed. A library of 10 imidazolium‐carboxylic acids was obtained in five to six steps from enantiopure l‐tert‐leucinol. In addition, four well‐defined Pd(DMBPA)‐NHC palladacycles were synthesized in good to excellent yields from the corresponding imidazolium precursors. These complexes were tested in a prototypical C(sp³)−H arylation reaction, and the most active one afforded the indoline product in low yield but significant enantioselectivity. These new bifunctional NHCs could find broader applications in catalytic enantioselective transformations occurring under milder conditions.

中文翻译：

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手性NHC-羧酸盐作为Pd催化对映选择性CH活化的潜在配体的设计

尽管付出了许多努力，但通过手性辅助配体或手性碱通过Pd ⁰催化的C（sp ³）-H活化合成规模碳和杂环仍然受到限制。受最近报道的IBiox型NHC配体和双官能配体在类似转化中的出色表现的启发，设计了带有羧基侧基的新型双官能NHC配体。在从对映体纯五到六步得到的10咪唑羧酸甲库升-叔-leucinol。此外，还从相应的咪唑鎓前体以良好至极好的收率合成了四种定义明确的Pd（DMBPA）-NHC Palladacycles。这些复合物在原型C（sp ³）-H芳基化反应，最活跃的反应以低收率但对映选择性显着提供了吲哚啉产物。这些新的双功能NHC在较温和条件下发生的催化对映选择性转化中可以找到更广泛的应用。