Ruthenium-Catalyzed Formal Dehydrative [4 + 2] Cycloaddition of Enamides and Alkynes for the Synthesis of Highly Substituted Pyridines: Reaction Development and Mechanistic Study
作者:Jicheng Wu、Wenbo Xu、Zhi-Xiang Yu、Jian Wang
DOI:10.1021/jacs.5b06400
日期:2015.7.29
Reported herein is a ruthenium-catalyzed formal dehydrative [4 + 2] cycloaddition of enamides and alkynes, representing a mild and economic protocol for the construction of highly substituted pyridines. Notably, the features of broad substrate scope, high efficiency, good functional group tolerance, and excellent regioselectivities were observed for this reaction. Density functional theory (DFT) calculations
本文报道了一种钌催化的烯酰胺和炔烃的正式脱水 [4 + 2] 环加成反应,代表了一种用于构建高度取代吡啶的温和且经济的方案。值得注意的是,该反应具有底物范围广、效率高、官能团耐受性好和优异的区域选择性等特点。已经进行了密度泛函理论 (DFT) 计算和实验以了解其机制和区域化学。DFT 计算表明,这种正式的脱水 [4 + 2] 反应始于 Ru 催化剂中的乙酸酯基团对烯酰胺的协同金属化去质子化,从而生成六元钌环中间体。然后炔烃插入到六元钌环的 Ru-C 键中,产生八元钌环中间体。羰基(最初来自烯酰胺底物并与八元钌环中间体中的 Ru 中心配位)然后插入 Ru-C 键中得到中间体,通过进一步脱水产生最终的吡啶产物。炔插入步骤是区域决定步骤,并且优选使所用炔的芳基远离催化剂以避免芳基与六元钌环中的烯酰胺部分排斥并保持与催化剂之间的共轭。芳基和炔烃的三CC键。因此,所用炔烃的芳基位于最终吡啶的β位,本