Reaction of lithium diisopropylamide (LDA) with (η 4 -1,3-buadiene)Fe(CO) 3 complexes bearing carboester functionalized side chains at C-5 gives eight- to ten-membered lactones as the major products after electrophilic quenching. However, treatments of the complexes with LDA, under an atmosphere of carbon monoxide, furnish bridged bicyclo[5.2.1]decane and bicyclo[6.2.1]undecane lactone skeletons as the major products.