A novel and practical synthesis of L-hexoses from D-glycono-1,5-lactones

A novel and efficient conversion of D-glycono-1,5-lactones into the corresp onding L-sugars is described. The important intermediate, delta-hydroxyalko xamates, was provided by a practical alkoxyamination of D-glycono-1,5-lacto nes mediated by Me3Al. In contrast to the preparation of beta-lactam skelet ons from beta-hydroxyalkoxamates, the cyclization of delta-hydroxyalkoxamat es under Mitsunobu conditions resulted in O-alkylation rather than N-alkyla tion. It is noteworthy that delta-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 efficientl y converted into the L-sugars.