Construction of a Fused Polycyclic Wall within the Cyclodextrin Belt To Ensure a Distorted Cavity: An Unusual trans ‐Diequatorial Ring‐Opening Reaction of Cyclodextrin Epoxide Rings

In the nucleophilic ring‐opening reaction of 2 X ,3 X ‐ manno ‐epoxides, the incoming nucleophiles attack the 3 X ‐C position of the epoxide almost exclusively. However, a quite unusual but very interesting reversed regioselectivity is observed when intramolecular hydroxy groups act as nucleophiles, that is, only the attack by 3 X −1 ‐OH at the 2 X ‐C position of the epoxide is observed. The reaction affords the apparent trans ‐diequatorial products and ensures an efficient construction of fused heterocycles within the cyclodextrin belt. In the case of 2 I ,3 I :2 II ,3 II ‐di‐ manno ‐epoxy‐β‐cyclodextrin, a tandem‐type reaction is initiated by the attack by the 3 VII ‐OH group at the 2 I ‐C position to generate a fused pentacycle. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)