Subscribe to RSS
DOI: 10.1055/s-2008-1042682
Chiral Macrocyclic Ytterbium Complex Catalysis in Aqueous Media
Contributor(s):Hisashi Yamamoto, Joshua N. PayettePublication History
Publication Date:
21 February 2008 (online)
Key words
ytterbium - Henry reaction - macrocyclic complexes
Significance
Chiral lanthanide complexes are now being investigated as catalysts for a variety of reductions and C-C bond-forming reactions (M. Shibasaki, N. Yoshikawa Chem. Rev. 2002, 102, 2187). However, non-aqueous reaction conditions are necessary due to the hydrolytic instability of many of these complexes. In the present work the authors report that chiral ytterbium complex 1 efficiently catalyzes the Henry reaction in aqueous media. Various pyruvate salts were utilized to give nitro-aldol products in moderate to good yields and enantioselectivities.
Comment
This paper is related to the work of Dickins and co-workers (Chirality 2005, 17, 357) where diaqua-ytterbium(III) complexes were found to catalyze the reduction of various α-keto acids by NaBH4 in aqueous solution. The authors conducted 1H NMR spectroscopic studies to probe the catalytic mechanism. It was found that the modest enantioselectivities result from equilibration between the Si- and Re-chelated pyruvate adducts and the absence of a preferred, reactive chelated intermediate. This new class of Yb catalysts has vast potential for future applications in aqueous processes.