Co-Catalyzed Asymmetric Intramolecular [3+2] Cycloaddition of Yne-Alkylidenecyclopropanes and its Reaction Mechanism
Co-Catalyzed Asymmetric Intramolecular [3+2] Cycloaddition of Yne-Alkylidenecyclopropanes and its Reaction Mechanism
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共催化不对称分子内[3 2]环加成炔亚烷基环丙烷及其反应机理
DOI：
10.1002/chem.202100426
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Yu Zhi-Xiang
中科院分区：
文献类型：
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作者：
Xiao Xiong;Yu Zhi-Xiang
由于手性 FMC 在各种功能分子中普遍存在，开发新的过渡金属催化不对称环加成反应来合成五元碳环 (FMC) 是反应发展的研究前沿。这里报告的是我们使用廉价的Co催化剂和市售手性配体(S)-Xyl-BINAP，发现炔-亚烷基环丙烷(yne-ACP)与双环[3.3.0]辛二烯和双环[4.3.0]壬二烯分子进行高度对映选择性的分子内[3+2]环加成。该反应避免了使用贵重的 Pd 和 Rh 催化剂，而这些催化剂通常是 ACP 的 [3+2] 反应的选择。本反应中对映体过量可高达92%。实验建议使用阳离子钴（I）物质作为催化物质。 DFT计算表明，这种[3+2]反应从炔烃和ACP的氧化环金属化开始，然后环丙基(CP)开环并还原消除形成环加合物。这一机制与以往ACP的[3+2]反应不同，后者通常从CP裂解开始，而不是从氧化环化开始。
Developing new transition metal‐catalyzed asymmetric cycloadditions for the synthesis of five‐membered carbocycles (FMCs) is a research frontier in reaction development due to the ubiquitous presence of chiral FMCs in various functional molecules. Reported here is our discovery of a highly enantioselective intramolecular [3+2] cycloaddition of yne‐alkylidenecyclopropanes (yne‐ACPs) to bicyclo[3.3.0]octadiene and bicyclo[4.3.0]nonadiene molecules using a cheap Co catalyst and commercially available chiral ligand (S)‐Xyl‐BINAP. This reaction avoids the use of precious Pd and Rh catalysts, which are usually the choices for [3+2] reactions with ACPs. The enantiomeric excess in the present reaction can be up to 92 %. Cationic cobalt(I) species was suggested by experiments as the catalytic species. DFT calculations showed that this [3+2] reaction starts with oxidative cyclometallation of alkyne and ACP, followed by ring opening of the cyclopropyl (CP) group and reductive elimination to form the cycloadduct. This mechanism is different from previous [3+2] reactions of ACPs, which usually start from CP cleavage, not from oxidative cyclization.