Total synthesis of albolic acid and ceroplastol II, 5–8–5-membered tricyclic insect sesterterpenoids, via a lactol-regulated silyloxy–Cope rearrangement

Optically active albolic acid and ceroplastol II, 5–8–5-membered tricyclic sesterterpenoids, were stereoselectively synthesised from two C10 synthons (iridoids)via CrCl2-condensation, lactol-regulated silyloxy–Cope rearrangement with a normally disfavoured boat transition geometry, TiCl2-ring closure, and C5-homologation.