期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 9, 期 18, 页码 4405-4413出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200305078
关键词
aldehydes; allylation; asymmetric synthesis; Lewis acids; titanium
A new, chiral bis-Ti-IV oxide of type 3 has been designed and can be utilized for strong activation of aldehyde carbonyls, thereby allowing a new catalytic enantioselective allylation of aldehydes with allyltributyltin. The chiral bis-Ti-IV catalyst (SS)-3 can be readily prepared either by treatment of bis(triisopropoxy)titanium oxide with (S)-BINOL or by treatment of ((S)-binaphthoxy)isopropoxytitanium chloride with silver(I) oxide. Treatment of hydrocinnamaldehyde with allyltributyltin under the influence of chiral bis-Ti-IV oxide (S,S)-3 generated in situ (10 mol %) in CH2Cl2 afforded an allylation product in 84 % yield and with 99 % ee. This asymmetric allylation with non-racemic bis-Ti-IV oxide 3 and partially resolved (S)BINOL shows a positive nonlinear effect in correlation of the enantiopurity of the allylation product with the ee of the (S)-BINOL. Chiral bis-Ti-IV oxide (S,S)-3 can also be utilized for related reactions such as asymmetric methallylation and propargylation of aldehydes with high enantioselectivity. This asymmetric approach provides a very useful way of obtaining high reactivity and selectivity through the simple introduction of the M-O-M unit into the design of chiral Lewis acid catalysts.
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