A straightforward route to enantiopure pyrrolizidines and indolizidines bycycloaddition to pyrroline N-oxides derived from the chiral pool

Enantiomerically pure, five membered cyclic nitrones, easily obtained in la rge amounts from protected hydroxyacids and aminoacids such as D- and L-tar taric, L-malic, and L-aspartic acids, give cycloaddition reactions with a g ood diastereocontrol. The adducts of L-malic and L-aspartic acids derived f rom addition of nitrones to dimethyl maleate and gamma-crotonolactone were easily converted into enantiopure pyrrolizidinones, which can be transforme d into polyhydroxypyrrolidines or polyhydroxypyrrolizidines, both interesti ng compounds as potential glycosidase inhibitors. The method is suitable fo r natural products synthesis as exemplified by a straightforward and conven ient access to the pyrrolizidine alkaloid necine base (-)-hastanecine, as w ell as to indolizidine alkaloids, i.e. (+)-lentiginosine.