Easy access to modified cyclodextrins by an intramolecular radical approach

A simple method to modify the primary face of cyclodextrins (CDs) is described. The 6I‐O‐yl radical of α‐, β‐, and γ‐CDs regioselectively abstracts the H5II, 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 C2‐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.Financial support by the Investigation Programs of the Ministerio de Economía y Competitividad (CTQ2010‐18244) and the COST Action CM1201 “Biomimetic Radical Chemistry” is acknowledged. D.A.‐D. thanks the Ministerio de Economía y Competitividad for a fellowship.Peer Reviewe