Syntheses of (+)-costic acid and structurally related eudesmane sesquiterpenoids and their biological evaluations as acaricidal agents against <i>Varroa destructor</i>

Synthesis of (+)-costic acid, isolated from Dittrichia viscosa (L.) W. Greuter as a natural acaricidal sesquiterpenoid, was achieved in 16 steps (R)-carvone with an overall yield 4.8%, involving the radical cyclization selenoester to construct decalone framework key step. Other structurally related products, (+)-costal, (+)-costol, and (+)-β-selinene, were also synthesized. The activities these four products some synthetic intermediates evaluated against Varroa destructor. Among them, (+)-costal especially exhibited potent activity.