Synthesis of Highly Condensed Polycyclic Carbohydrates by Reaction of a Spirocyclic Enamino Sulfonate Derived from D-Xylofuranose with Bifunctional Reagents

摘要

The appropriately substituted 5-O-tosyl derivative(1),easily prepared from 1,2-O-isopropylidene-alpha-D-xylofuranose,serves as a useful precursor for the preparation of highly condensed cyclic carbohydrates.The synthesis involves a first cyclization of the 5-O-tosyl sugar derivative 1 to a highly reactive cyclic enamine,which subsequently undergoes the nucleophilic attack of a bifunctional reagent X(CH2)_n Z in a regio-and stereospecific way.Finally,a spontaneous cyclization step allows the formation of a stereochemically defined extra ring,fused to the sugar backbone.The functionalization and size of this ring can be varied by the proper choice of the bifunctional reagent.X-ray diffraction analysis and intensive NMR studies with one of these carbohydrates were performed to highlight the strained nature of these compounds.