An efficient constructive method for a tricyclic system: an important intermediate for the synthesis of tricycloclavulone

The tricyclic ring system of tricycloclavulone was synthesized from 2-methoxycarbonyl-2-cyclopenten-1-one (2). Key reactions include Lewis acid-catalyzed [2+2]-cycloaddition of α,β-unsaturated ester 2 with thioacetylene derivatives and construction of the A-ring by using the Grubbs catalyst.