Development of second generation of anionic tethered NHC ligand for achievement of reversal of enantioselectivity in catalytic asymmetric reaction

在此之前，我们利用ch2桥接羟基酰胺功能化的偶氮盐实现了cu催化的不对称共轭加成（ACA）反应。现在，我们设计并合成了一种（CH2）2桥羟基酰胺功能化偶氮盐。与Cu(OTf)2与（CH2）2桥接的偶氮盐在ACA反应中得到的产物相比，Cu(OTf)2与（CH2）2桥接的配体结合生成了构型相反的1,4-加合物。此外，通过将Cu预催化剂从Cu(OTf)2改为Cu(acac)2，可以观察到与相同配体前体的ACA反应的双对映选择性控制。此外，还开发了一种新型的酯-酰胺功能化偶氮盐。结果表明，酯酰胺功能化偶氮盐与羟基酰胺功能化偶氮盐在ACA反应中得到的共轭加合物的绝对构型不同。

Previously, we achieved the Cu-catalyzed asymmetric conjugate addition (ACA) reaction by the use of a CH2-bridged hydroxy-amide-functionalized azolium salt. Now, we designed and synthesized a (CH2)2-bridged hydroxy-amide-functionalized azolium salt. In comparison with the product which was obtained in the ACA reaction by Cu(OTf)2 combined with CH2-bridged azolium salt, the combination of Cu(OTf)2 with (CH2)2-bridged ligand led to the formation of the 1,4-adduct with opposite configuration. In addition, dual enantioselective control in the ACA reaction with the same ligand precursor was observed by changing the Cu precatalyst from Cu(OTf)2 to Cu(acac)2. Furthermore, a new ester-amide-functionalized azolium salt was also developed. It was found that the absolute configuration of the conjugate adduct in the ACA reaction using the ester-amide-functionalized azolium salt differs from that obtained in the ACA reaction using the hydroxy-amide-functionalized azolium salt.