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  • Title: Preparation of 4,6-cyclo-hexopyranoses by palladium-mediated intramolecular cyclodehalogenation.
    Author: Wessel HP, Viaud MC, Gardon V.
    Journal: Carbohydr Res; 1993 Jul 19; 245(2):233-44. PubMed ID: 8370023.
    Abstract:
    4,6-Cyclo-4,6-dideoxy-hexapyronoses were obtained by palladium-mediated intramolecular cyclodehalogenation. Thus, methyl 2,3-di-O-acetyl-4,6-dideoxy-4,6-diiodo-beta-D-galactopyranoside (3) afforded methyl 2,3-di-O-acetyl-4,5-cyclo-4,6-dideoxy-beta-D-galactopyranoside (5) in 56% yield upon treatment with hydrogen in the presence of palladium-on-charcoal and diethylamine. The structure of 5 was proven by MS, NMR including NOE measurements, and by independent conversion of 4 to 5 by zinc-mediated Wurtz synthesis. Similarly, methyl 2,3-di-O-acetyl-4,6-cyclo-4,6-dideoxy-alpha-D-galactopyranoside (6) and O-(2,3,-di-O-acetyl-4,6-cyclo-4,6-dideoxy-alpha-D-galactopyranosyl)-(1-- >4)-1,2,3,6-tetra-O-acetyl-beta-D-glucopyranose (17) were obtained along with the respective 4,6-dideoxy analogues. Also methyl 2,3-di-O-acetyl-4,6-dideoxy-4,6-diiodo-beta-D-glucopyranoside (19) gave galacto-configured 5 stereoselectively.
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