Synthesis of optically active indolizidines: (-)-8a-epi-dendroprimine and (-)-7,8-dehydro-5,6-dimethylindolizidine

Indolizidinones can be employed as key intermediates in efficient asymmetri c synthesis of naturally occurring indolizidine alkaloid analogues. The 5,7 -dimethylindolizidine (-)-8a-epi-dendroprimine was formed by a diastereosel ective methylation-reduction sequence of the lactam function. The (-)-5,6-d imethylindolizidine was generated via the same key step including an additi onal quasi 1,2-methyl shift: an intramolecular enamine alkylation is follow ed by regioselective reductive cyclopropane ring opening.