Mechanistic studies on the stereoselective formation of glycosyl iodides: first characterization of β- d-glycosyl iodides

• Published in: Carbohydrate research Vol. 300; no. 2; pp. 119 - 125
• Main Authors: Gervay, Jacquelyn, Nguyen, Truc N., Hadd, Michael J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 12-05-1997
• Subjects: Glycosyl iodides; NMR characterization; β- d-Glycosyl iodides; Glycosyl iodides; NMR characterization; β- d-Glycosyl iodides
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/S0008-6215(96)00321-7

Treatment of glycosyl acetates with one equivalent of iodotrimethylsilane at low temperature results in the quantitative formation of glycosyl iodides. Carbohydrates that possess a participating group at the C-2 position initially form β-
d-glycosyl iodides, which quickly equilibrate to the α-iodo anomers. The β anomer of peracetylated glucose reacts faster than the α anomer, presumably because the C-2 acetate can assist in displacing the silylated anomeric acetate. In contrast, the α anomer reacts faster than the β anomer in substrates lacking a participating group at C-2. For example, activation of
1-O-
acetyl-2,3,4,6-tetra-O-
benzyl-α-
d-glucopyranose
leads to formation of the β iodide, while the corresponding β acetate produces the α iodide. Although the β iodides quickly equilibrate to the α anomers, they can be prepared in sizable quantities at low temperatures where equilibration is slow. This report describes the first stereoselective formation and characterization of β-
d-glycosyl iodides.