AZA-WITTIG REACTION OF SUGAR ISOTHIOCYANATES AND SUGAR IMINOPHOSPHORANES - AN EASY ENTRY TO UNSYMMETRICAL SUGAR CARBODIIMIDES

Aldohexose derivatives possessing a triphenylphosphoranylideneamino su bstituent at the primary (C-6) position exhibit an increased reactivit y towards the aza-Wittig condensation with isothiocyanates as compared with glycosyl phosphinimines. The reaction is particularly fast and e fficient in the case of glycosyl isothiocyanates and has been exploite d in the preparation of (1-->6)-linked pseudooligosaccharides incorpor ating carbodiimide bridges. These compounds are excellent starting mat erials for the preparation of sugar ureas, thioureas and guanidines by reaction with the appropriate nucleophile. (C) 1997 Elsevier Science Ltd.