Chromium-Catalyzed Alkene Isomerization with Switchable Selectivity
Jiaoyue Zhong, Xuelan Wang, Meiming Luo*, Xiaoming Zeng*
*Key Laboratory of Green Chemistry and Technology, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, China,
Email: luommscu.edu.cn, zengxiaoming
scu.edu.cn
J. Zhong, X. Wang, M. Luo, X. Zeng, Org. Lett., 2024, 26, 3124-3129.
DOI: 10.1021/acs.orglett.4c00737
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Abstract
A chromium catalyst enables an isomerization of alkenes over multiple carbon atoms to give the most thermodynamically stable isomers in the presence of HBpin/LiOtBu. The same catalyst allows for the selective isomerization of terminal alkenes over one carbon atom without an additive, exhibiting efficient and controllable alkene transposition selectivity.
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Scope of Isomerizing Alkenes over One Carbon Center
proposed mechanism
Details
The document discusses a study on a chromium-catalyzed system for alkene isomerization with switchable selectivity. The system uses a single chromium catalyst (CrCl2/dtbpy/Mg) that can selectively produce different internal alkene isomers. In the presence of HBpin/LiOtBu, the catalyst enables the isomerization of alkenes over multiple carbon atoms to yield thermodynamically stable isomers. Without additives, the catalyst selectively isomerizes terminal alkenes over one carbon atom. This method offers a straightforward and atom-economic strategy for creating high-value compounds with minimal skeletal modification and byproduct formation. The study highlights the challenge of achieving high stereo- and regioselectivity in alkene isomerization and the potential of using a single metal catalyst with additive-responsive selectivity. The research demonstrates the versatility of the chromium catalyst system, which can tolerate various functional groups and achieve good yields and high stereoselectivity. Mechanistic studies suggest that the isomerization occurs via a π-allyl−Cr intermediate without HBpin/LiOtBu and via an alkyl−Cr mechanism with HBpin/LiOtBu. This catalytic approach adds value to existing metal-catalyzed alkene transposition reactions and offers a new tool for synthetic chemistry.
Key Words
ID: J54-Y2024