Total synthesis of absinthin.

(+)-Absinthin, a structurally unique triterpene, has been efficiently constructed in nine reaction steps and in 18.6% overall yield from O-acetylisophotosantonic lactone. The synthesis features Mitsunobu arylselenylation, oxidative elimination of allylic arylselenides, biomimetic dimerization via regio- and stereospecific Diels−Alder reaction, and a four-step stereochemical inversion of a highly sterically congested tertiary alcohol. This approach has not only tackled the formidable synthetic challenges in assembling structurally complex (+)-absinthin but also paved an efficient synthetic route to a series of medicinally attractive absinthin analogues.