Spacer-Mediated Synthesis of Bis-spiroketal Disaccharides: Nonsymmetrical Furanose-Pyranose Difructose Dianhydrides

Abstract

The stereochemical outcome of the dimerization reaction of D-fructose, leading to tricyclic bis-spiroketal systems, can be tuned by inserting a xylylene template between the reacting ­moieties. Spirocyclization becomes then an intramolecular process, the available conformational space depending on the nature of the tether. The methodology is here illustrated by the stereoselective synthesis of two nonsymmetrical di-D-fructose dianhydrides present in commercial caramel.