Deoxy and bridged cyclodextrins

Chelation of aluminum reagent between position 6 and the endocyclic oxygen on unit A is highly sensitive to the steric hindrance exerted by the groups on adjacent sugars, especially by the one on the primary position of the counterclockwise 

In the case of fS-cyclodextrin, the lack of symmetry makes the duplication of the double de-O-benzylation more challenging. Indeed, if we consider that the second deprotection wiU take place on opposite positions, de-O-benzylation can lead to four regioisomers. 

These two approaches, the so-called bascule-bridge and the deoxy-sugars, are complementary and allow a regioselective access to two tridifferentiated P-cyclodextrins. 

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