Insight into the Modes of Activation of Pyridinium and Bipyridinium Salts in Non‐Covalent Organocatalysis
作者:Robin Weiss、Tamara Golisano、Patrick Pale、Victor Mamane
DOI:10.1002/adsc.202100865
日期:2021.10.19
A series of pyridinium and bipyridinium salts were prepared and their catalytic properties were evaluated in the aza-Diels-Alder reaction between imines and Danishefsky diene. Depending on the substituents of the pyridinium/bipyridinium rings and on the nature of the counterion, two mechanisms of activation were demonstrated. In case of non-substituted rings, the substrate is activated through charge
制备了一系列吡啶鎓盐和联吡啶鎓盐,并在亚胺和丹麦谢夫斯基二烯之间的氮杂-狄尔斯-阿尔德反应中评估了它们的催化性能。根据吡啶鎓/联吡啶鎓环的取代基和抗衡离子的性质,证明了两种活化机制。在未取代环的情况下,底物通过涉及亚胺 C 侧芳环的电荷转移而被激活。当在催化剂上引入卤素原子时,活化模式切换到涉及亚胺氮孤对的卤素键。此外,排除了基于氢键和自由基阳离子的替代激活模式。这项工作使我们能够开发出两类催化剂,它们的潜力在各种亚胺与丹麦谢夫斯基二烯的环加成反应中得到了证明。第一个家族由简单的甲基吡啶三氟甲磺酸盐和二辛基联吡啶三氟甲磺酸盐组成。前者仅对带有 a 的亚胺有效发现 C 侧的对甲氧基苯基和后者对于在亚胺的 N 侧和 C 侧带有不同取代基的亚胺是有效的。第二类是基于卤化吡啶鎓盐,它被证明对几乎所有考虑的亚胺都有活性。