Asymmetric alkylation of aldehydes catalyzed by novel dinuclear bis-BINOLate titanium(IV) complexes

Dinuclear bis-BINOLate titanium(IV) complexes catalyzes asymmetric alkylation of aldehydes even in the presence of a reduced amount of titanium tetraisopropoxide (0.2 equiv). Bis-BINOLs 1a, b in which two BINOL units are tethered by o- and m-phenylenebis(ethynyl) groups form stable dinuclear bis-BIN...

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Bibliographic Details
Published in:Tetrahedron: asymmetry 2004-12, Vol.15 (24), p.3879-3883
Main Authors: Harada, Toshiro, Kanda, Kousou, Hiraoka, Yuuki, Marutani, Yasuhisa, Nakatsugawa, Masashi
Format: Article
Language:English
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Summary:Dinuclear bis-BINOLate titanium(IV) complexes catalyzes asymmetric alkylation of aldehydes even in the presence of a reduced amount of titanium tetraisopropoxide (0.2 equiv). Bis-BINOLs 1a, b in which two BINOL units are tethered by o- and m-phenylenebis(ethynyl) groups form stable dinuclear bis-BINOLate titanium(IV) complexes 2a, b by treatment with titanium tetraisopropoxide. In the presence of excess titanium tetraisopropoxide, 2a and 2b (2–20 mol %) catalyze diethylzinc addition to aromatic and aliphatic aldehydes in an efficient manner to give the ethylation products with high enantioselectivities. While more than 1 equiv of titanium tetraisopropoxide (with respect to a substrate aldehyde) is generally employed for obtaining high turnover frequency and selectivity in reactions catalyzed by a parent (BINOLate)Ti(O i Pr) 2, the amount can be reduced as low as 0.2 equiv in the reactions catalyzed by 2a, b.
ISSN:0957-4166
1362-511X
DOI:10.1016/j.tetasy.2004.11.008