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Chiral, coordinatively-saturated cobaltate(III) complexes of Schiff bases obtained from salicylaldehyde and the optically active amino acids, (S)-Val, (S)-Thr, and (S)-Trp, are formed as C2-symmetrical, octahedral, anionic Λ(S,S)-, and Δ(S,S)-diastereoisomeric complexes, which are easily separable by chromatography. The complexes are stereochemically inert and, thus, are not transformed into each other under normal conditions. The counter-cations of the complexes can be easily interchanged and the sodium, potassium, and silver salts of some of the complexes were prepared. The structures of diastereoisomeric Λ-[(Sal-(S)-Val)2Co(III)]-Ag+ and Δ-[(Sal-(S)-Val)2Co(III)]-Ag+ were established by single crystal X-ray analysis. All of the sodium and potassium complexes effectively catalyzed the reaction between benzaldehyde and Me3SiCN, but only the Λ-[(Sal-(S)-Trp)2Co(III)]-K+ complex gave rise to enantiomerically-enriched mandelonitrile with up to 77% ee. The silver salts catalyzed a Mukaiyama reaction with low enantioselectivity (ee in the range 6-27%). © 2008 Elsevier Ltd. All rights reserved.
Author(s): Belokon YN, Maleev VI, Kataev DA, Mal'fanov IlyaL, Bulychev AG, Moskalenko MA, Saveleva TF, Skrupskaya TV, Lyssenko KA, Godovikov IA, North M
Publication type: Article
Publication status: Published
Journal: Tetrahedron: Asymmetry
Year: 2008
Volume: 19
Issue: 7
Pages: 822-831
ISSN (print): 0957-4166
ISSN (electronic): 1362-511X
Publisher: Pergamon
URL: http://dx.doi.org/10.1016/j.tetasy.2008.03.010
DOI: 10.1016/j.tetasy.2008.03.010
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