期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 142, 期 30, 页码 13180-13189出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.0c05647
关键词
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资金
- NIGMS [2R01GM109054]
- University of Chicago
- International Postdoctoral Exchange Fellowship Program 2017 from the Office of China Postdoctoral Council
- NSF
Synthesis of bridged scaffolds via Type II cyclization constitutes substantial challenges due to the intrinsic ring strain accumulated in reaction transition states. Catalytic enantioselective Type II-cyclization methods are even rarer. Here, we describe a detailed study of developing a Rh(I)-catalyzed enantioselective intramolecular Type II cyclization of alkynes via C-C activation of cyclobutanones. This method offers a rapid approach to access a wide range of functionalized [3.3.1]-bridged bicycles along with an exocyclic olefin and an all-carbon quaternary stereocenter. Excellent enantioselectivity has been achieved using a combination of cationic rhodium(I) and DTBM-segphos. Attributed to the redox neutral and strong acid/base-free reaction conditions, high chemoselectivity has also been observed. For the oxygen-tethered substrates, the reaction can proceed at room temperature. In addition, partial kinetic resolution has been achieved for substrates with existing stereocenters, forging interesting chiral tricyclic scaffolds. The methylalkyne-derived substrates gave unexpected dimeric structures in good yield with excellent enantioselectivity and complete diastereoselectivity. Furthermore, the bridged bicyclic products can be diversely functionalized through simple transformations. Finally, mechanistic studies reveal a surprising reaction pathway that involves forming a metal-stabilized anti-Bredt olefin intermediate.
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