Studies towards the construction of quaternary indolizidines by [2,3]-sigmatropic rearrangement cocatalyzed by ionic liquid

an efficient enantioselective approach for preparation of quaternary centers from proline 5 building block has been developed through [2,3]-sigmatropic stevens rearrangement co-catalyzed by ionic liquid. the sigmatropic rearrangement was stereospecific because the [2,3]-migrations were restricted to the same face, and the stereoselectivity arose from the previous n-alkylation step in 8. the approach showed better yields than described in literature. the use of 1-butyl-3-methylimidazolium hexafluorophosphate showed an improvement in the yields of the stevens rearrangement due to a possible stabilization and/or activatation of zwiterionicspecies in solution by the ionic liquid. several indolizidine moieties were synthesized from quaternary proline derivative (s)-5.