Regio- and Stereocontrolled Selective Debenzylation and SubstitutionReactions of C-2 Formyl Glycals. Application in the Synthesis ofConstrained β-Sugar Amino Acids

摘要

O-Benzyl-protected C-2 formyl glycals are regioselectively deprotected and acetylated first at C-3 andthen at C-6 upon treatment with a ZnCl_2-Ac_2O-AcOH reagent combination. Treatment of thethus-obtained C-3 acetate with various nucleophiles leads to substitution at C-3 with retention ofstereochemistry in the galactal series, whereas mixed results were obtained with glucal-derivedcompounds. Two of the azido-substituted products were converted into the corresponding β-sugaramino acids.