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

Cycloadditions of 3,4-isopropylidenedioxy-?¹-pyrroline-1-oxide (9), (3S,4S)-3,4-bis(methoxy-methoxy)-?¹-pyrroline-N-oxide (28), and its (3R, 4R)-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.