Reductive Radical Cascades Triggered by Alkoxyl Radicals in the beta-Cyclodextrin Framework

The generation and fate of 2(I-VII),3(I-VII),6(II-VII)-icosa-O-methyl-beta-cyclomaltoheptaos-6(I)-O-yl radical under reductive conditions is described. Two radical cascade reactions are involved: the main one is triggered by a 1,8-HAT of the hydrogen at 5(VII)C. The radical can reach the anomeric hydrogen at 1(V)C three sugar units ahead using a six-step sequence. The different hydrogen donor ability of the group 14 hydrides permits one to selectively stop the cascade at (SC)-C-VII, 2(VI)C, and 4(VI)C to obtain beta-CD with a beta-L-Idop unit, acyclic hepta-, and hexa-saccharide structures, respectively.