The Polonovski reaction of castanospermine tetraacetate N-oxide with acetic anhydride gave (�)-1-acetoxy-8-hydroxy-2,3-dihydro-lH-indolizinium acetate (10) by aromatization of the piperidine ring. N- Bromosuccinimide oxidation of castanospermine tetraacetate gave a low yield (4%) of (+)-2-bromo-5,6,7,8-tetrahydroindolizine-6,7,8-triyl triacetate (13), by aromatization of the pyrrolidine ring.