The three-dimensional structure of carbohelicenes has fascinated generations of molecular chemists and has been exploited in a wide range of applications. Their strong circularly polarized luminescence has attracted considerable attention in recent years due to promising applications in new optical materials. Although the enantioselective synthesis of fused carbo- and heterohelicenes has been achieved, a direct catalytic enantioselective method allowing the synthesis of lower, non-fused carbo[n]helicenes (n = 4–6) is still lacking. We report here that Pd-catalysed enantioselective C–H arylation in the presence of a unique bifunctional phosphine-carboxylate ligand provides a simple and general access to these lower carbo[n]helicenes. Computational mechanistic studies indicate that both the C–H activation and reductive elimination steps contribute to the overall enantioselectivity. The observed enantio-induction seems to arise from a combination of non-covalent interactions and steric repulsion between the substrate and ligand during the two key reductive elimination steps. The photophysical and chiroptical properties of the synthesized scalemic [n]helicenes have been systematically studied.

carbohelicenes 的三维结构令几代分子化学家着迷，并已在广泛的应用中得到开发。近年来，由于其在新型光学材料中的应用前景，其强圆偏振发光引起了相当大的关注。 尽管已经实现了稠合碳-和杂杂碳烯的对映选择性合成，但仍然缺乏一种直接催化对映选择性方法来合成低级非稠合碳[n ]杂碳烯（n = 4-6）。我们在此报告，在独特的双功能膦-羧酸配体存在下，Pd 催化的对映选择性 C-H 芳基化提供了一种简单且通用的途径来获得这些低碳 [ n]螺旋烯。计算机理研究表明，C-H 活化和还原消除步骤都有助于整体对映选择性。在两个关键的还原消除步骤中，观察到的对映体诱导似乎是由底物和配体之间的非共价相互作用和空间排斥的组合引起的。已经系统地研究了合成的 scalemic [ n ] helicenes的光物理和手性光学性质。