Synthesis of some novel 1-(5-thio-β-D-xylopyranosyl)-lumazine and -pyrimidine nucleosides
作者:Najim A. Al-Masoudi、Wolfgang Pfleiderer
DOI:10.1016/s0040-4020(01)87232-x
日期:1993.8
4-Tetra-O-acetyl-5-thio-D-xylopyranose (1) reacts with the silylated lumazine bases (2–5) under trimethylsilyl trifluoromethylsulfonate catalysis to give the nucleosides 6, 8, 10, and 12 respectively, which face deblocking with potassium carbonate in dry methanol to yield the free nucleosides 17, 9, 11, and 13 respectively. The synthesis of 1-(2,3,4-tri-O-acetyl-5-thio-β-xylopyranosyl)-thymine (17) and
Novel chiral xylofuranose-based phosphinooxathiane and phosphinooxazinane ligands have been synthesized and found to be effective ligands for palladium-catalyzedasymmetric tandem allylic allylations of 1,4-diacetoxy-cis-2-butene with 2-(benzylamino)ethanol or 1,2-bis[benzylamino]ethane to give chiral 4-benzyl-2-vinylmorpholine (94% ee) or 1,4-dibenzyl-2-vinylpiperazine (70% ee).
Novel chiral xylofuranose-based phosphinooxathiane and phosphinooxazinane ligands were found to provide high levels of enantioselectivity (up to 94% ce) in palladium-catalyzed asymmetric allylic alkylations and aminations. (C) 2003 Elsevier Ltd. All rights reserved.
A Kinetic Isotope Effect Study on the Hydrolysis Reactions of Methyl Xylopyranosides and Methyl 5-Thioxylopyranosides: Oxygen versus Sulfur Stabilization of Carbenium Ions
作者:Deepani Indurugalla、Andrew J. Bennet
DOI:10.1021/ja011232g
日期:2001.11.1
(J. Am. Chem. Soc. 1986, 108, 7287-7294) KIEs for the acid-catalyzed hydrolysis of methyl alpha- and beta-glucopyranosides, it is possible to conclude that at the transition state for xylopyranoside hydrolysis resonance stabilization of the developing carbenium ion by the ring oxygen atom is coupled to exocyclic C-O bondcleavage, and the corresponding methyl glucopyranosides hydrolyze via transition