title: Towards alpha- or beta-D-C-glycosyl compounds by tin-catalyzed addition of glycosyl radicals to acrylonitrile and vinylphosphonate, and flexible reduction of tetra-O-acetyl-alpha-D-glucopyranosyl bromide with cyanoborohydride.
abstract: Photo-induced radical addition of acetylated alpha-D-glucopyranosyl bromide (1). to acrylonitrile or diethyl vinylphosphonate, in the presence of catalytic amounts of tri-n-butyltin chloride and sodium (or tetra-n-butylammonium) cyanoborohydride in excess, allowed efficient preparations of alpha-configurated nonononitrile and 2-(alpha-D-glucopyranosyl)-ethylphosphonate (79, 70% yields, respectively). These conditions led to 2-(alpha-D-manno-, and galactopyranosyl)-ethylphosphonates in 68 and 76% yields. Similarly, radical addition of acetylated 1-bromo-beta-D-glucopyranosyl chloride (2). to acrylonitrile or diethyl vinylphosphonate afforded mainly intermediate chlorides which, upon radical reduction with excess tri-n-butyltin hydride, afforded the corresponding beta anomers (40 and 38%, respectively) by sequential C-C and C-H bond formation. Stereocontrol relies on the alpha-stereoselective quenching of D-glycopyranos-1-yl radicals. We found also that UV light irradiation of 1 with excess NaBH(3)CN in tert-butanol afforded either 1,3,4,6-tetra-O-acetyl-2-deoxy-alpha-D-arabino-hexopyranose (65% after crystallization) or, when 10% mol thiophenol was added, 2,3,4,6-tetra-O-acetyl-1,5-anhydro-D-glucitol (79%). These are simple, tin-free, and easily controlled conditions, which compare well with known preparations of these reduced sugars.
authors.affiliation: Université Claude-Bernard Lyon I, UMR CNRS-Université 5622, ESCPE-Lyon, Bâtiment 308, 43, Boulevard du 11 Novembre 1918, F-69622, Villeurbanne, France. jean-piere.praly@univ-lyonl.fr
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Praly
authors.forename: Azin Salek
authors.initials: AS
authors.lastname: Ardakani
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bruyère
authors.forename: Chrystelle
authors.initials: C
authors.lastname: Marie-Luce
authors.forename: Bing
authors.initials: B
authors.lastname: Bing Qin
mesh_terms: D000107:Acetylation; D000181:Acrylonitrile / Q000737:chemistry*; D001894:Borohydrides / Q000737:chemistry*; D002236:Carbohydrate Conformation; D002384:Catalysis; D002712:Chlorides / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry*; D006031:Glycosylation; D063065:Organophosphonates / Q000737:chemistry*; D009947:Organotin Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D014466:Ultraviolet Rays; D014753:Vinyl Compounds / Q000737:chemistry*
chemical_list: D001894:Borohydrides; D002712:Chlorides; D005609:Free Radicals; D006027:Glycosides; D063065:Organophosphonates; D009947:Organotin Compounds; D014753:Vinyl Compounds; D000181:Acrylonitrile