Total Synthesis of Aplydactone by a Conformationally Controlled C-H Functionalization.

A concise, protecting-group-free total synthesis of the unusual brominated sesquiterpene aplydactone is described. Our synthesis features a [2+2] photocycloaddition, a Wolff ring contraction, an unusual remote C-H functionalization to establish the highly strained tetracyclic core, and a hydrogen-atom transfer (HAT) reaction to access the bromine-containing stereocenter. A finely tuned conformation of the α-diazoketone precursor is the key for the success of the late-stage transannular C-H insertion to deliver a bridged six-membered ring and a quaternary stereocenter (C6) between two quaternary carbon atoms (C1 and C7).