Easy Access to Modified Cyclodextrins by an Intramolecular Radical Approach

A simple method to modify the primary face of cyclodextrins (CDs) is described. The 6 I ‐ O ‐yl radical of α‐, β‐, and γ‐CDs regioselectively abstracts the H5 II , located in the adjacent D ‐glucose unit, by an intramolecular 1,8‐hydrogen‐atom‐transfer reaction through a geometrically restricted nine‐membered transition state to give a stable 1,3,5‐trioxocane ring. The reaction has been extended to the 1,4‐diols of α‐ and β‐CD to give the corresponding bis(trioxocane)s. The C 2 ‐symmetric bis(trioxocane) corresponding to the α‐CD is a stable crystalline solid whose structure was confirmed by X‐ray diffraction analysis. The calculated geometric parameters confirm that the primary face is severely distorted toward a narrower elliptical shape for this rim.