Utilisation d'ylides du phosphore en chimie des sucres. XX. Synthèse de sucres acétyléniques et réarrangment d'intermédiaires carbénoïdes. Communication préliminaire

Two novel methods for the synthesis of terminal acetylenic sugars, both involving a chain extension by one carbon unit, are described. In the first procedure, an aldehydo-sugar is treated with dibromomethylenetriphenyl-phosphorane, then with n-butyllithium and finally with water. The second method involves an one-step reaction between an aldehydo-sugar and dimethyl diazomethylphosphonate. The acetylenic sugars obtained are valuable synthetic intermediates for the preparation of heterocyclic C-nucleosides by 1,3-dipolar cycloaddition reactions and some examples of syntheses of this type are described. Treatment of keto-sugars with dimethyl diazomethylphosphonate led to an intermediate carbenoid species which reacted by insertion into a C? H bond in one case and underwent nucleophilic attack by a methoxy group in a second case.