Synthesis of trihydroxylated pyrrolizidines and indolizidines using cycloaddition reactions of functionalized cyclic nitrones, and the synthesis of (+)- and (−)-lentiginosine

Abstract

Cycloadditions of 3,4-isopropylidenedioxy- Δ 1-pyrroline-1-oxide ( 9), (3 S,4 S)-3,4-bis(methoxymethoxy)- Δ 1-pyrroline- N-oxide ( 28), and its (3 R,4 R)-enantiomer, with suitably-functionalized alkenes has led to the synthesis of the 1,2,6-trihydroxypyrrolizidines 14, 33 and ent-33 , and the 1,2,7-trihydroxyindolizidines 22,39 and ent-39 . Deoxygenation of two enantiomeric intermediates in these syntheses led to the preparation of the dihydroxylated indolizidine (+)-lentiginosine and its (−)-enantiomer.