A Novel and Practical Synthesis ofl-Hexoses fromd-Glycono-1,5-lactones

A novel and efficient conversion of d-glycono-1,5-lactones into the corresponding l-sugars is described. The important intermediate, δ-hydroxyalkoxamates, was provided by a practical alkoxyamination of d-glycono-1,5-lactones mediated by Me3Al. In contrast to the preparation of β-lactam skeletons from β-hydroxyalkoxamates, the cyclization of δ-hydroxyalkoxamates under Mitsunobu conditions resulted in O-alkylation rather than N-alkylation. It is noteworthy that δ-hydroxyalkoxamates derived from d-mannono-1,5-lactones afforded the O-alkylation product in 91% yield. None of the N-alkylation product was detected in this case. These O-cyclized oximes, in which the inversion of the configuration at C5 was secured, were efficiently converted into the l-sugars.