Two new synthetic routes to a number of tetracyclic intermediates, for the total synthesis of some diterpenoids incorporating the bicyclo[3.2.1]octane moiety, are described. The syntheses of the bicyclo[3,2,1]octane derivatives begin with preparation of the hydroaromatic γ,δ-unsaturated acids 6, 15 and 17, and proceed via the α-diazomethyl ketones to the corresponding pentacyclic ketones 20, 24 and 26 by an intramolecular carbenoid insertion reaction, followed by a regiospecific acid-catalysed cleavage of the aromatic conjugated cyclopropane bond to the respective unsaturated ketones 27, 29 and 30. The second route to these unsaturated ketones involves a single step boron trifluoride etherate catalysed intramolecular alkylation in the corresponding α-diazomethyl ketones. The tetracyclic ketones 31, 34 and 35 were obtained in quantitative yields by a regiostereospecific hydrogenolytic cleavage of the aromatic conjugated cyclopropane bond in the respective pentacyclic precursors with PdC in ethanol. Under the same conditions, reduction of the styrenoid bond in the ketones 29 and 30 proceeds stereospecifically leading to 34 and 35 respectively, whereas the unsaturated ketone 27 gave a mixture of epimeric ketones 31 and 32 in a ratio of 69:31.