Syntheses of pyrrolizidines and indolizidines from α,β-unsaturated sugar δ-lactones via Dieckmann condensation

Both N-methoxycarbonylmethyl- and N-methoxycarbonylethyl-derivatives of dihydroxy-(d)-homoproline were subjected to the intramolecular ester condensation to yield ketoesters of pyrrolizidine and indolizidine series, respectively. The former ketoester was transformed into derivative related to australine, while the latter were transformed into the natural lentiginosine as well as its 2-epi-, and 7-hydroxy-2-epi-derivatives.