A SHORT, CHIROSPECIFIC SYNTHESIS OF THE ANT VENOM ALKALOID (3R,5S,8S)-3,5-DIALKYLPYRROLIZIDINES

The stereospecific synthesis of both (+)-xenovenine (1) and (+)-(3R,5S,8S)-3-methyl-5-(8-nonenyl)pyrrolizidine (2), found in ant venom, is described. The stereoselective intramolecular amidomercuration of the N-alkenylurethane 3, available from D-alanine, followed by oxidative demercuration provides the trans pyrrolidine alcohol 5. Thereafter, oxidation of 5 followed by Horner-Wadsworth-Emmons elongation of the ring appendage affords the relevant bicyclic precursors 7 and 9, which are stereoselectively converted into 1 and 10, respectively, by catalytic hydrogenation. The pyrrolizidine 10 is readily transformed into 2 by elaboration of the side chain at C5.