Abstract: Herbarumin Ⅲ, a naturally occurred phytotoxin which has a ten-membered lactone ring, was isolated from Phoma herbarum. The root growth inhibiting activity of Herbarumin Ⅲ is ten times than 2,4-dichlorophenoxyacetic acid. The stereoselective total synthesis of Herbarumin Ⅲ (3), along with its 8-epimer 22, was succeeded in 13 steps starting from n-butyraldehyde and 1,5-pentandiol on the bassis of Brown's asymmetric allylation, with modified Julia olefination and Yamaguchi's macro-lactonization as the key steps.

Key words: Herbarumin Ⅲ, Asymmetric allylation, Modified Julia olefination, Yamaguchi’s macro-lactonization