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.