- Novel Water-Soluble Bisphosphinite Chiral Ligands Derived from α,α- And β,β-Trehalose. Application to Asymmetric Hydrogenation of Dehydroamino Acids and Their Esters in Water or an Aqueous/ Organic Biphasic Medium
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Novel 2,3:4,6-di-O-isopropylidene-α-D-glucopyranosyl-(1,1)-4,6-O-isopropylidene- 2,3-di-O-diphenylphosphino-α-D-glucopyranoside (2), 2,3:4,6-di-O-cyclohexylidene-α-D-glucopyranosyl-(1,1)-4,6-O- cyclohexylidene-2,3-di-O-diphenylphosphino-α-D-glucopyranoside (4), and 2,3:4,6-di-O-cyclohexylidene-β-D-glucopyranosyl-(1,1)-4,6-O- cyclohexylidene-2,3-di-O-diphenylphosphino-β-D-glucopyranoside (11) were prepared from the corresponding α,α- or β,β-trehalose. The ligands were transformed into cationic Rh complexes, such as [Rh(α-D-glucopyranosyl-(1,1)-2,3-di-O-diphenylphosphino-α-D- glucopyranoside)(cod)]BF4 (3) and [Rh(β-D-glucopyranosyl-(1,1)-2,3-di-O-diphenylphosphino-β-D- glucopyranoside)(cod)]BF4 (12) bearing free hydroxy groups. These complexes were soluble in water and were efficient catalysts for the asymmetric hydrogenation of dehydroamino acids and their esters in water or an aqueous/organic biphasic medium with high enantioselectivity (up to 99.9% ee). Aqueous biphasic systems offer an easy separation of the aqueous catalyst phase from the product phase and allow recycling of the catalyst phase without the loss of enantioselectivity.
- Yonehara, Koji,Hashizume, Tomohiro,Mori, Kenji,Ohe, Kouichi,Uemura, Sakae
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p. 5593 - 5598
(2007/10/03)
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- SYNTHESIS OF UNSYMMETRICAL TREHALOSE ANALOGUES BY SILVER TRIFLUOROMETHANESULPHONATE PROMOTED GLYCOSYLATIONS
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The coupling of benzoylated glucosyl bromides with 2,3,4,6-tetra-O-benzylated gluco, manno or galacto-pyranoses promoted by silver triflate is described, and the compositions of the crude reaction mixtures, determined by 13C NMR spectroscopy, are presente
- Roennow, Tor E. C. L.,Meldel, Morten,Bock, Klaus
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p. 197 - 212
(2007/10/02)
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- Synthesis and glycosylation shift of 1,1'-disaccharides
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Nineteen kinds of nonreducing 1,1'-disaccharides have synthesized by modified Koenigs-Knorr method, and characterized by NMR. The glycosylation shift of each anomeric carbon has been estimated.
- Nishizawa,Kodama,Yamane,Kayano,Hatakeyama,Yamada
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p. 982 - 984
(2007/10/02)
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- A NOVEL OBSERVATION ON KOENIGS-KNORR CONDENSATION OF 2,3,4,6-TETRA-O-ACETYL-α-D-GLUCOPYRANOSYL BROMIDE WITH METHYL 4,6-O-BENZYLIDENE-α-D-GLUCOPYRANOSIDE
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As a result of condensation between methyl 4,6-O-benzylidene-α-D-glucopyranoside and bromo-2,3,4,6-tetra-O-acetyl-α-D-glucopyranose in 1,2-dichloroethane in presence of silver carbonate, after removal of functional groups, the following substances were ob
- Temeriusz, Andrzej,Piekarska, Boguslawa,Radomski, Jan,Stepinski, Janusz
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p. 141 - 147
(2007/10/02)
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