Palladium-Catalyzed Carbene Migratory Insertion Using Conjugated Ene鈥揧ne鈥揔etones as Carbene Precursors

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• 作者：Ying Xia ; Shuanglin Qu ; Qing Xiao ; Zhi-Xiang Wang ; Peiyuan Qu ; Li Chen ; Zhen Liu ; Leiming Tian ; Zhongxing Huang ; Yan Zhang ; Jianbo Wang
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：September 11, 2013
• 年：2013
• 卷：135
• 期：36
• 页码：13502-13511
• 全文大小：766K
• 年卷期：v.135,no.36(September 11, 2013)
• ISSN：1520-5126

文摘

Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene鈥搚ne鈥搆etones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation鈥揷yclization, palladium carbene migratory insertion, 尾-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate, which is supported by DFT calculations. The palladium carbene character of the key intermediate is validated by three aspects, including bond lengths, Wiberg bond order indices, and molecular orbitals, by comparison to those reported for stable palladium carbene species. Computational studies also revealed that the rate-limiting step is ene鈥搚ne鈥搆etone cyclization, which leads to the formation of the palladium (2-furyl)carbene, while the subsequent carbene migratory insertion is a facile process with a low energy barrier (<5 kcal/mol).