The concise synthesis of two polyhydroxyquinolizidines from 2,3-O-isopropylidene-d-ribofuranose was accomplished. Epimerization of the intermediate N-(3-alkenyl)nitrone resulted in exceptionally straightforward access to an iminosugar with a d-arabino configuration. A plausible mechanism of the epimerization via nitrone-enehydroxylamine tautomerism explaining the reaction course has been proposed.