Radical Reactions of Carbohydrates

Volume II: Radical Reactions in Carbohydrate Synthesis

Chapter 4: Selenides and Tellurides
Chapter 4 is in a portable document file (pdf) and can be viewed by clicking the blue, Chapter 4 button below. The drawing underneath the button pictures the formation and reaction of a carbohydrate radical produced from a carbohydrate selenide. Beside the drawing is a description of the reaction. Below the drawing and its description is a summary of Chapter 4.

Chapter 4: Selenides and Tellurides

This drawing show a radical cyclization reaction beginning with a phenyl selenide.

Drawing Description

Selenophenyl glycosides are com-parable in reactivity to glycosyl bromides, but they have a synthetic advantage over glycosyl iodides and bromides when it comes to radical formation because the phenyl selenides are thermally more stable than glycosyl bromides and much more stable than glycosyl iodides. In the drawing shown on the left (Scheme 8 in Chapter 4) a phenyl selenide is involved in the linking together of two saccharide units.

Summary of Chapter 2

Reactions of carbohydrate selenides with tin-centered and silicon-centered radicals pro­duce carbon-centered, carbohydrate radicals. These radicals can undergo hydrogen-atom abstraction, intra- and intermolecular addition, group migration, radical-cation formation, and radical combination. Reduction and radical cyclization are the two most common of these reactions. Reduction is involved in the synthesis of 2-deoxy sugars and 2'-deoxy disaccha­rides and nucleosides. Cyclization, which is characterized by the formation of compounds with a variety of ring sizes, is the central reaction in a general procedure for converting monosaccharides into C-disaccharides. In this procedure glycosyl phenyl selenides are chosen to generate pyranos-1-yl and furanos-1-yl radicals because, as mentioned in the drawing description, a carbohydrate with a selenophenyl group at C‑1 is thermally more stable than substrates with the other C-1 substituents usually used for radical generation at this position. Carbohydrate tellurides are relatively unstable compounds that form carbohydrate radicals upon absorption of light or reaction with methyl radicals.