郑州大学牛俊龙/杨丹丹JACS:钴催化去对称环化对映选择性合成含多重手性元素的硼立体中心化合物
Catalytic asymmetric synthesis of boron-stereogenic compounds has garnered growing interest in recent years. However, strategies for constructing boron-stereogenic centers with structural diversity remain underdeveloped, especially compared with the well-established methods for carbon stereocenters formation. Herein, we report an earth-abundant cobalt-catalyzed enantioselective C–H activation/desymmetric annulation of arylamides with prochiral boron-diyne compounds, providing direct access to a wide range of boron-stereogenic heterocycles. Enabled by a cobalt(II)/chiral salicyloxazoline (Salox) catalytic system, this approach effectively addresses the challenge of precise differentiation between two enantiotopic alkyne units. The transformation concurrently establishes a stable boron-stereogenic center together with multiple chiral axes (N–N or C–N) in a single step, featuring a broad substrate scope, good functional group tolerance, and high efficiency. Gram-scale synthesis, directing-group removal, and versatile derivatizations further highlighted the synthetic utility of this strategy. Detailed experimental and computational studies provide in-depth insight into the catalytic mechanism. Notably, the obtained optically pure compounds exhibit promising photoluminescence and circularly polarized luminescence (CPL) properties, underscoring their potential for advanced optical applications.图4. 合成含N-N手性轴的硼立体中心化合物底物拓展 (图片来源于JACS)图5. 合成含C-N手性轴的硼立体中心化合物底物拓展 (图片来源于JACS)图6. 合成应用和构型稳定性研究 (图片来源于JACS)图7. 机理研究、DFT计算及可能的反应机理 (图片来源于JACS)图8. 光物理和光学属性研究 (图片来源于JACS)In conclusion, we disclosed a catalytic strategy employing an earth-abundant cobalt catalyst for achieving the direct, enantioselective assembly of boron-stereogenic heterocycles. Through C−H activation/desymmetric annulation of arylamides and boron-diynes, the cobalt(II)/Salox system enables precise discrimination of the two enantiotopic alkyne units, thus facilitating the simultaneous construction of a boron stereogenic center and multiple chiral axes in a single step. This protocol features a broad substrate scope (66 examples), high efficiency, and excellent stereoselectivity, affording a diverse array of chiral boron products with favorable configurational stability. The robustness of this method is demonstrated by gram-scale synthesis, directing-group removal, and synthetic transformations. Experimental and DFT studies on the mechanism reveal that the reductive elimination is both the rate-determining and stereodetermining step. Moreover, the synthesized chiral boron compounds exhibit attractive photophysical properties, including high photoluminescence quantum yields and remarkable circularly polarized luminescence, thus establishing them as promising candidates for chiroptical materials. This work represents a significant advance in the construction of main-group heteroatom stereogenic centers via earth-abundant cobalt-catalyzed enantioselective C−H func tionalization.
