Stereocontrolled synthesis of (-)-galanthamine.

An enantioselective synthesis of (-)-galanthamine has been realized in 11 linear steps starting from isovanillin. A Mitsunobu aryl ether forming reaction was used to assemble the galanthamine backbone, which was stitched together using enyne ring-closing metathesis, Heck, and N-alkylation reactions affording the tetracyclic ring system. Control of relative and absolute stereochemistry was derived from an easily accessible enantiomerically enriched propargylic alcohol 13.