期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 137, 期 36, 页码 11838-11845出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.5b07827
关键词
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资金
- MEXT [21245028, 25708018, 15K17824, 23105546, 15H00943]
- ACT-C from JST
- Frontier Research Base for Global Young Researchers, Osaka University, on the Program of MEXT
- Grants-in-Aid for Scientific Research [15H05803, 15K17824, 15H00943, 25708018] Funding Source: KAKEN
A highly enantioselective synthesis of 3-aryl-, vinyl-, and alkynyl-2,1-benzoxasiloles (up to 99.9% ee and 99% yield) was achieved via the sequential activation of an aldehyde and a silane by nickel(0). This strategy was applied to a simultaneous generation of carbon- and silicon-stereogenic centers with excellent selectivity (dr = 99:1) via diastereotopic aryl transfer. Initial mechanistic studies revealed the complete switching of an aryl-transfer process from an intermolecular (racemic synthesis in the presence of IPr) to an intramolecular (enantioselective synthesis using chiral NHC, L5) fashion. A plausible rationale for the switching of the aryl-transfer process is given by a preliminary DFT calculation, which suggests that the coordination of 1 to the nickel(0)/L5 fragment in an eta(2)-arene:eta(2)-aldehyde fashion would be a key to the intramolecular process, while the formation of the corresponding intermediate is not possible in the presence of IPr. Owing to the chemically labile nature of its C-Si and O-Si bonds, enantioenriched benzoxasiloles are utilized for the synthesis of chiral building blocks and antihistaminic and anticholinergic drug molecules such as (R)-orphenadrine and (S)-neobenodine with no erosion of the enantiomeric excess.
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