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

Cycloadditions of 3,4-isopropylidenedioxy-Delta(1)-pyrroline-1-oxide (9), (3S,4S)-3,4-bis(methoxy-methoxy)-Delta(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 lit, 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. (C) 1998 Elsevier Science Ltd. All rights reserved.