Radical Reactions of Carbohydrates

Volume II: Radical Reactions in Carbohydrate Synthesis

Chapter 21: Reactions of Radicals Produced by Electron Transfer to Manganese(III) Acetate and Ammonium Cerium(IV) Nitrate

Chapter 22 is in a portable document file (pdf) and can be viewed by clicking the blue, Chapter 22 button below. The drawing underneath the button pictures the frontier orbitals in radical addition to a glycal. Beside the drawing is a description of the orbital interaction. Below the drawing and its description is a summary of Chapter 22.

Chapter 22: Reactions of Radicals Produced by Electron Transfer to Manganese(III) Acetate and Ammonium Cerium(IV) Nitrate

This drawing show Frontier Orbital interactions during radical addition.

Drawing Description

Atomic orbital coefficients can be useful in explaining regio-selectivity in a radical-addition reaction if, as is usually the case, the reaction has an early transition state. In such a reaction the rate constant for the carbon–carbon bond-forming step depends on the magnitude of the atomic orbital coefficients of the interacting frontier orbitals. The most effective position for bonding in the glycal 7 is at C-2 because the atomic orbital coefficient for the HOMO in 7 is larger at C-2 than at C‑1 (The drawing on the left is Figure 2 in Chapter 22).

Summary of Chapter 22

Manganese(III) acetate and ammonium cerium(IV) nitrate react with CH-acidic compounds to produce carbon-centered radicals that add to carbohydrates with electron-rich double bonds. The resulting adduct radicals usually undergo oxidation to produce cations, each of which captures a nucleophile and then deprotonates to complete the reaction. Most reported reactions of this type involve the malonyl radical adding to an unsaturated carbohydrate. When the carbohydrate is a glycal, this reaction is a regiospecific addition to C-2. Such an addition takes place stereoselectively from the less hindered face of the ring system. Radical addition also occurs to less electron-rich double bonds, but the adduct radical is not oxidized to a cation; instead, it abstracts a hydrogen atom. Manganese(III) acetate also reacts with unsaturated carbohydrates to produce lactones.