Mechanistic Analysis of Azine N-Oxide Direct Arylation: Evidence for a Critical Role of Acetate in the Pd(OAc)2 Precatalyst

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• 作者：Ho-Yan Sun ; Serge I. Gorelsky ; David R. Stuart ; Louis-Charles Campeau ; Keith Fagnou
• 刊名：Journal of Organic Chemistry
• 出版年：2010
• 出版时间：December 3, 2010
• 年：2010
• 卷：75
• 期：23
• 页码：8180-8189
• 全文大小：1149K
• 年卷期：v.75,no.23(December 3, 2010)
• ISSN：1520-6904

文摘

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.