A short, practical synthesis of the ant venom alkaloid, three (3R,5S,8aS)-3-alkyl-5-methylindolizidines

A short, practical and diastereoselective method for preparing the ant venom alkaloid, three (3R,5S,8aS)-3-alkyl-5-methylindolizidines (1–3), has been developed. The stereoselective intramolecular amidomercuration of the N-alkenylurethane 4 followed by oxidative demercuration provides the piperidine alcohol cis-6 as a major product. Thereafter, oxidation of cis-6 followed by the Horner-Emmons elongation of the ring appendages affords the enones 8, 10, and 11, which are stereoselectively converted into 1, 2, and 3, respectively, by catalytic hydrogenation.