Radical Reactions of Carbohydrates

Volume II: Radical Reactions in Carbohydrate Synthesis

Chapter 9: Phosphoric Acid Esters

Chapter 9 is in a portable document file (pdf) and can be viewed by clicking the blue, Chapter 9 button below. The drawing underneath the button shows the reaction of a pyranos-1-yl radical containing a phosphatoxy group at C-2 to produce an ion pair consisting of a radical cation and an anion. Beside the drawing is a description of the reaction. Below the drawing and its description is a summary of Chapter 9.

Chapter 9: Phosphoric Acid Esters

This drawing describes the mechanism for phosphatoxy group migration.   

Drawing Description

A proposed radical cation formation from a pyranos-1-yl radical that has a phosphatoxy group at C-2 is pictured in the drawing on the left. (This is Scheme 2 in Chapter 9). The first radical cation produced is the contact ion pair (CIP) 2.  Solvent polarity determines whether group migration or formation of free ions will be the major reaction pathway for 2.

Summary of Chapter 9

Under the proper conditions a phosphatoxy group that is β-related to a radical center will fragment to produce an ion pair consisting of a phosphate anion and a radical cation. This heterolytic fragmentation is favored by polar solvents and formation of radical cations at least as stable as those arising from enol ethers. When the radical center is at C-1 in a pyranoid or furanoid ring, the ion pair recombines to give a new radical in which phosphatoxy group migration to C-1 is accompanied by radical translocation to C-2. If the radical center in a nucleotide is at C-4' and a phosphatoxy group is located at C-3', heterolytic cleavage of the bond between C-3' and O-3' does not lead to group migration; rather, products arising from hydrogen-atom abstraction, solvent capture, or proton loss are observed.