Glycosylations with a septanosyl fluoride donor lacking a C2 protecting group

Involvement of an Oxonium Ion Intermediate in Controlling the Diastereoselectivity of Nucleophilic Substitution Reactions of Septanoses

The alkoxy substituents at C4 and C2 of septanoses control the stereochemical outcomes of O-glycosylation reactions of these seven-membered-ring intermediates. Isolation of a bicyclic acetal byproduct in some substitution reactions suggests that the C4 benzyloxy substituent engaged in long-range participation, stabilizing intermediates by the formation of an oxonium ion intermediate. Inductive destabilization of the carbocationic intermediate provided by the C2 substituent is crucial to the participation of the remote alkoxy group.

A practical and scalable synthesis of carbohydrate based oxepines

An efficient, seven-step synthesis of carbohydrate based oxepines is reported using per-O-acetyl septanoses as key intermediates. The scope of the synthesis was evaluated by varying both the pyranose starting materials and protecting groups incorporated into the oxepine products. The practicality of the method make it amenable to scale up as demonstrated by the gram-scale synthesis of the d-glucose derived oxepine.