Atropisomeric Phosphine Ligands Bearing C–N Axial Chirality: Applications in Enantioselective Suzuki–Miyaura Cross-Coupling Towards the Assembly of Tetra-ortho-Substituted Biaryls,Journal of the American Chemical Society

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Atropisomeric Phosphine Ligands Bearing C–N Axial Chirality: Applications in Enantioselective Suzuki–Miyaura Cross-Coupling Towards the Assembly of Tetra-ortho-Substituted Biaryls
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-08-03 , DOI: 10.1021/jacs.2c06240
Kin Boon Gan ₁ , Rong-Lin Zhong _{1,

2} , Zhen-Wei Zhang _{1,

3} , Fuk Yee Kwong ₁

Affiliation

Biaryl phosphines bearing C_(Ar)–C_(Ar) axial chirality are commonly known and have been successfully applied in many asymmetric catalyses. Nevertheless, the development of a chiral ligand having an axially chiral C_(Ar)–N backbone remains elusive due to its undesirable less restricted rotational barrier. In fact, it is highly attractive to overcome this challenge in ligand development as the incorporation of an N-donor component at the chiral axis is more favorable toward the transient metal coordination, and thus, a better outcome of stereocommunication is anticipated to the approaching substrates. Herein, we present a rational design of a new collection of chiral phosphines featuring a C–N axial chirality and their applications in enantioselective Suzuki–Miyaura cross-coupling for accessing highly steric hindered tetra-ortho-substituted biaryls (26 examples up to 98:2 er). It is worth noting that the embodied carbazolyl framework is crucial to succeed the reaction, by the fruitful steric relief of bulky substrate coordination and transmetalation via a fleeting Pd–N jumping to Pd-π fashion. DFT calculation reveals an interesting Pd-arene-walking characteristic across the carbazolyl plane for attaining a lower energy-preferred route in a catalytic cycle. The theoretical study successfully predicts the stereooutcome and matches the enantioselectivity with the experimental results.

中文翻译：

带有 C-N 轴向手性的阻转异构膦配体：在对映选择性 Suzuki-Miyaura 交叉偶联中用于四邻位取代联芳基组装的应用

_{带有 C (Ar)} -C _(Ar)轴向手性的联芳基膦是众所周知的，并已成功应用于许多不对称催化剂中。然而，开发具有轴向手性 C _{(Ar)的手性配体}-N 骨架由于其不受欢迎的较少限制的旋转屏障而仍然难以捉摸。事实上，克服配体开发中的这一挑战非常有吸引力，因为在手性轴上掺入 N 供体组分更有利于瞬态金属配位，因此，预计接近的底物会有更好的立体通信结果. 在此，我们提出了一种新的具有 C-N 轴向手性的手性膦的合理设计及其在对映选择性 Suzuki-Miyaura 交叉偶联中的应用，以获得高位阻四邻-取代的联芳基（26 个实例，最高 98:2 er）。值得注意的是，通过短暂的 Pd-N 跃迁到 Pd-π 方式，大量的底物配位和金属转移有效地释放空间位阻，体现的咔唑基框架对于反应的成功至关重要。DFT 计算揭示了一个有趣的 Pd-芳烃在咔唑平面上的行走特性，用于在催化循环中获得较低能量的首选路线。理论研究成功地预测了立体结果，并将对映选择性与实验结果相匹配。

更新日期：2022-08-03

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