Résumé
The installation of the 2-furyl ring at the anomeric carbon of 2,3,4,6-tetra-
O-benzyl-
D-glucopyranose and 2,3:5,6-di-
O-isopropylidene-
D-mannofuranose is carried out either by addition of 2-lithiofuran to the correspondinglactones either by direct
C-glycosidation of the
O-acetyl derivatives with furan; the resultant 2-furyl
C-glycosides are converted to carboxylic acids by the oxidative cleavage of the furan nucleous.
Same methodology to α- and β-
C-mannofuranosyl carboxylates