Synthetic photochemistry. Part 44. Total synthesis of ceroplastol II and albolic acid, 5-8-5-membered tricyclic sesterterpenoid insect wax constituents, via stereocontrolled silyloxy-Cope rearrangement with a normally disfavoured transition state

To a 1,5-diene, prepared by CrCl2-mediated condensation of two iridoid synthons, was appended a lactol moiety, which was subjected to a stereocontrolled silyloxy-Cope rearrangement to give, via a normally disfavoured boat transition geometry, a thermolysate, from which the total synthesis of optically active Ceroplastol II and albolic acid, 5-8-5-membered tricyclic sesterterpenoids, was accomplished for the first time.