Rhodium-Catalyzed C-H Activation of Phenacyl Ammonium Salts Assisted by an Oxidizing C-N Bond: A Combination of Experimentaland Theoretical Studies
Rhodium-Catalyzed C-H Activation of Phenacyl Ammonium Salts Assisted by an Oxidizing C-N Bond: A Combination of Experimentaland Theoretical Studies
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氧化性 C-N 键辅助的铑催化苯甲酰铵盐的 C-H 活化：实验与理论研究的结合
DOI：
10.1021/ja511796h
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发表时间：
2015
影响因子：
15
通讯作者：
Xingwei Li
中科院分区：
文献类型：
--
作者：
Songjie Yu;Song Liu;Yu Lan;Boshun Wan;Xingwei Li
Rh（III）催化的C-H活化辅助的氧化导向基团已经发展到一个温和的和氧化还原经济的策略，用于杂环的建设。尽管取得了成功，但这些偶联系统目前仅限于氧化N-O或N-N键的裂解。氧化C-N键的断裂，这使得互补的碳环合成，是前所未有的。本文设计了一种具有氧化性C-N键的α-铵基苯乙酮作为Rh（III）催化的C-H活化反应的底物。与α-重氮酯偶联得到苯并环戊酮，与未活化的烯烃如苯乙烯和脂肪族烯烃偶联得到邻位烯化苯乙酮。在这两个系统中，反应进行了广泛的范围，高效率，和官能团的宽容。以α-溴代苯乙酮和三乙胺为起始原料，实现了重氮酯的高效一锅法偶联。用实验和理论相结合的方法研究了偶氮酯的反应机理。特别是，三个不同的机制途径已被仔细检查的DFT研究，这表明，C-H激活发生通过C-结合烯醇化辅助协调金属化-去质子化机制，是限速的。在随后的C-C形成步骤中，最低能量途径涉及两种铑卡宾物质作为关键中间体。
Rh(III)-catalyzed C–H activation assisted by an oxidizing directing group has evolved to a mild and redox-economic strategy for the construction of heterocycles. Despite the success, these coupling systems are currently limited to cleavage of an oxidizing N–O or N–N bond. Cleavage of an oxidizing C–N bond, which allows for complementary carbocycle synthesis, is unprecedented. In this article, α-ammonium acetophenones with an oxidizing C–N bond have been designed as substrates for Rh(III)-catalyzed C–H activation under redox-neutral conditions. The coupling with α-diazo esters afforded benzocyclopentanones, and the coupling with unactivated alkenes such as styrenes and aliphatic olefins gaveortho-olefinated acetophenoes. In both systems the reactions proceeded with a broad scope, high efficiency, and functional group tolerance. Moreover, efficient one-pot coupling of diazo esters has been realized starting from α-bromoacetophenones and triethylamine. The reaction mechanism for the coupling with diazo esters has been studied by a combination of experimental and theoretical methods. In particular, three distinct mechanistic pathways have been scrutinized by DFT studies, which revealed that the C–H activation occurs via a C-bound enolate-assisted concerted metalation–deprotonation mechanism and is rate-limiting. In subsequent C–C formation steps, the lowest energy pathway involves two rhodium carbene species as key intermediates.