Divergent Cycloaddition and Ring-Closing Metathesis Approaches to Indolizidine and Pyrrolo[1,2-a]azepine Skeletons from a Chiral Precursor: An Expeditious Route to (−)-8-epi-Swainsonine Triacetate

[reaction: see text] A divergent strategy for the synthesis of diverse azabicyclic ring systems has been developed in which a chiral N-allylpyrrolidine derivative, obtained from a carbohydrate precursor was converted to (-)-8-epi-swainsonine triacetate by RCM and to a pyrrolo[1,2-a]azepine derivative and a 3-hydroxymethyl-substituted indolizidine by N-allylcarbohydrate nitrone and nitrile oxide cycloadditions.