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.
Stevens rearrangement; [2,3]-sigmatropic; indolizidines; ionic liquid; co-catalyzed
