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

The generation and fate of 2^I-VII,3^I-VII,6^II-VII-icosa- O-methyl-β-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^VIIC. The radical can reach the anomeric hydrogen at 1^VC 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 5^VIIC, 2^VIC, and 4^VIC to obtain β-CD with a β-l-Ido p unit, acyclic hepta-, and hexa-saccharide structures, respectively.