The synthesis of the title systems is described by cycloaddition of dimethylketen to cyclopentadiene, addition of hypobromous acid to the product and use of a nitrile-mediated rearrangement to give 4-cyano-6-exo-benzyloxy-3,3-dimethylbicylo[3.2.0]heptan-2-one(5b) and its dervatives by further modification.