School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150080, China.
Shenzhen Grubbs Institute and Department of Chemistry, Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen, Guangdong518055, China.
J Am Chem Soc. 2021 Oct 6;143(39):16302-16310. doi: 10.1021/jacs.1c08482. Epub 2021 Sep 27.
The construction of main group heteroatom-stereogenic compounds is of great importance due to their intriguing chemical, physical, biological, and stereoelectronic properties. Despite that organoboron compounds are widely used in organic chemistry, the creation of a tetrahedral boron-stereogenic center in one enantiomeric form remains highly challenging. Given the labile nature of ligands attached to the tetracoordinate boron atom, only a handful of enantioenriched boron-stereogenic compounds have been reported via resolution or a chiral substrate-induced diastereoselective approach. To date catalytic asymmetric synthesis of boron-stereogenic compounds has remained unknown. Here, we demonstrate the first catalytic enantioselective construction of boron-stereogenic compounds via an asymmetric copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. This enantioselective CuAAC reaction not only gives access to a wide range of novel highly functionalized boron-stereogenic heterocycles in high yields with good to excellent enantioselectivities but also produces optically active terminal alkyne and triazole moieties with various potential application prospects. Further transformation of the chiral tetracoordinate boron compounds delivers several complex heterocyclic entities bearing boron-stereogenic centers without the loss of enantiopurity. Moreover, the X-ray structure, the barrier to racemization, and the HOMO/LUMO gap of selected tetracoordinate boron compounds are investigated. Notably, these novel N,N π-conjugated boron-stereogenic compounds exhibit bright fluorescence. The optical properties, including circular dichroism, quantum yield, and circular polarized luminescence spectroscopies, are examined. These features expand the chemical space of the chiroptical boron-based dye platform, which could have great potential applications in chiral optoelectronic materials.
主族杂原子手性化合物的构建具有重要意义，因为它们具有有趣的化学、物理、生物和立体电子性质。尽管有机硼化合物在有机化学中被广泛应用，但在单一对映体形式中构建四面体硼手性中心仍然极具挑战性。鉴于连接到四配位硼原子的配体的不稳定性，仅通过拆分或手性底物诱导的非对映选择性方法报告了少数对映体富集的硼手性化合物。迄今为止，硼手性化合物的催化不对称合成仍然未知。在这里，我们通过不对称铜催化叠氮-炔环加成（CuAAC）反应证明了硼手性化合物的首次催化对映选择性构建。这种对映选择性 CuAAC 反应不仅可以以高收率和良好到优异的对映选择性获得广泛的新型高官能化硼手性杂环，而且还可以生成具有各种潜在应用前景的光学活性末端炔烃和三唑部分。手性四配位硼化合物的进一步转化可得到几个带有硼手性中心的复杂杂环实体，而不会损失对映体纯度。此外，还研究了所选四配位硼化合物的 X 射线结构、外消旋化势垒和 HOMO/LUMO 能隙。值得注意的是，这些新型 N,Nπ-共轭硼手性化合物表现出明亮的荧光。研究了它们的光学性质，包括圆二色性、量子产率和圆偏振发光光谱。这些特性扩展了手性基于硼的染料平台的化学空间，在手性光电材料中具有巨大的潜在应用。
