Center for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa 10 Marie Curie, Ottawa, Ontario, Canada K1N 6N5.
J Org Chem. 2010 Dec 3;75(23):8180-9. doi: 10.1021/jo101821r. Epub 2010 Nov 5.
Detailed mechanistic studies on the palladium-catalyzed direct arylation of pyridine N-oxides are presented. The order of each reaction component is determined to provide a general mechanistic picture. The C-H bond cleaving step is examined in further detail through computational studies, and the calculated results are in support of an inner-sphere concerted metalation-deprotonation (CMD) pathway. Competition experiments were conducted with N-oxides of varying electronic characters, and results revealed an enhancement of rate when using a more electron-deficient species, which is in support of a CMD transition state. The effect of base on reaction rate was also examined and it was found that a carboxylate base was required for the reaction to proceed. This led to the conclusion that Pd(OAc)(2) plays a pivotal role in the reaction mechanism as more than merely a precatalyst, but also as a source of acetate base required for the C-H bond cleavage step.
呈现了钯催化吡啶 N-氧化物的直接芳基化的详细机理研究。通过确定每个反应组分的顺序，提供了一个普遍的机理图。通过计算研究进一步考察了 C-H 键断裂步骤，计算结果支持内球协同金属化-去质子化（CMD）途径。进行了具有不同电子特性的 N-氧化物的竞争实验，结果表明使用更缺电子的物种时，速率会提高，这支持了 CMD 过渡态。还研究了碱对反应速率的影响，发现反应需要羧酸盐碱。这得出结论，Pd(OAc)(2)在反应机制中起着关键作用，不仅是前催化剂，而且还是 C-H 键断裂步骤所需的醋酸盐碱的来源。
