A convenient route for the synthesis of oxacyclobutapentalene, the tricyclic bridged core structure present in bioactive marine diterpene bielschowskysin and the polyketide hippolachnin A, is reported. The key steps involve ring closing metathesis of a triene derived from D-mannitol to produce selectively the dihydrofuran derivative instead of the cyclopentene derivative and a Cu(I)-catalyzed intramolecular [2+2]photocycloaddition of the dihydrofuran derivative.
