期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 21, 期 52, 页码 19186-19194出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201406680
关键词
catalysis; cross-coupling; organoboron; palladium; stereoselectivity
资金
- Natural Science and Engineering Research Council of Canada
- University of Alberta
- NSERC Canada Graduate Scholarship-D
- Alberta Innovates Health Solutions Studentship
- Japan Society for the Promotion of Science (JSPS)
- Grants-in-Aid for Scientific Research [14J02341] Funding Source: KAKEN
A method for enantioselective desymmetrization of 1,1-diborylalkanes through a stereoselective Pd-catalyzed Suzuki-Miyaura cross-coupling has been thoroughly optimized. The most effective ligand was found to be a alpha,alpha,alpha,alpha-tetra-aryl-1,3-dioxolane-4,5-dimethanol (TADDOL)-derived phosphoramidite. Results show that in order to achieve high selectivity, a suitable balance between the sterics of the aryl groups and the amino group on the ligand must be achieved. While the base has been known to facilitate transme tallation in cross-coupling reactions, mechanistic studies on this desymmetrization process reveal that the base, in the presence of KHF2, likely plays an additional role in the hydrolysis of the pinacol boronates to the corresponding boronic acids. Through an in depth optimization of the chiral ligand and mechanistic studies, it was possible to obtain ee values over 90% for several aryl bromides and to develop a reliably scalable process (up to one gram of 1,1-diborylalkane substrate).
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