A new synthesis of tricyclic sesquiterpene (±)-sterpurene

A new synthesis of tricyclic sesquiterpene, sterpurene 1 is reported. An intermolecular [2+2]-photocycloaddition 14→15 serves as a key step, which is promoted through the stabilisation of the enone excited state through a β-carbomethoxy substituent on the α,β-unsaturated enone moiety. A tricyclo[6.3.0.03,6]undecane based advanced intermediate 19 en route to 1, has been fragmented to the bicyclo[6.3.0]undecane system 27 present in the asteriscane-type sesquiterpenoids.