New Access to Indolizidine and Pyrrolizidine Alkaloids from an Enantiopure Proline: Total Syntheses of (—)-Lentiginosine and (1R,2R,7aR)-Dihydroxypyrrolizidine.

A new approach to the synthesis of indolizidine and pyrrolizidine skeletons is reported. (-)-Lentiginosine and (1R,2R,7aR)-dihydroxypyrrolizidine have both been synthesized in 13 steps from di-O-isopropylidene- D-mannitol. The common key intermediate is (-)-dihydroxyproline benzyl ester 10. [ABSTRACT FROM AUTHOR]