Variations on the SnCl4 and CF3CO2Ag-promoted glycosidation of sugar acetates: a direct, versatile and apparently simple method with either alpha or beta stereocontrol.
Glycosidation of sugar peracetates (D-gluco, D-galacto) with SnCl(4) and CF(3)CO(2)Ag led to either 1,2-cis-, or 1,2-trans-glycosides, depending primarily on the alcohols used. In particular, 1,2-trans-glycosides, expected from acyl-protected glycosyl donors, were formed in high yields with alcohols sharing specific features such as bulkiness, presence of electron-withdrawing groups or polyethoxy motifs. In contrast, simple alcohols afforded approximately 1:1 mixtures of 2,3,4,6-tetra-O-acetyl, and 3,4,6-tri-O-acetyl 1,2-cis-glycosides due to anomerization and/or acid-catalyzed fragmentation of 1,2-orthoester intermediates. After reacetylation or deacetylation, acetylated or fully deprotected 1,2-cis-glycosides (alpha-D-gluco, alpha-D-galacto) were obtained in approximately 90% yields by a simple and direct method.
Xue
Jia Lu
JL
Université de Lyon, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires associé au CNRS, UMR 5246, Laboratoire de Chimie Organique 2, Bâtiment Curien, 43 boulevard du 11 Novembre 1918, F-69622 Villeurbanne, France.
Cecioni
Samy
S
He
Li
L
Vidal
Sébastien
S
Praly
Jean-Pierre
JP
D000085:Acetates / Q000737:chemistry*; D002384:Catalysis; D006027:Glycosides / Q000737:chemistry*; D006031:Glycosylation; D013237:Stereoisomerism; D013379:Substrate Specificity; D017971:Tin Compounds / Q000737:chemistry*; D014269:Trifluoroacetic Acid / Q000737:chemistry*
D000085:Acetates; D006027:Glycosides; D017971:Tin Compounds; C041694:stannic chloride; D014269:Trifluoroacetic Acid