Construction of Bridged and Fused Bicyclic Skeletons via Intramolecular Addition of Nucleophiles to (η⁴-Diene)Fe(CO)₃ Complexes Bearing Functionalized Side Chains

Reaction of lithium diisopropylamide (LDA) with (η⁴-1,3-cyclohexadiene)Fe(CO)₃ complexes bearing functionalized side chains at C-5, under an atmosphere of carbon monoxide, gives bridged bicyclo[3.2.1]octene and bicyclo[3.3.1]nonene systems after electrophilic quenching, whereas larger rings cannot be obtained in this series. Under the same reaction conditions, intramolecular cyclization of acyclic (η⁴-1,3-butadiene)Fe(CO)₃ complexes with functionalized side chains at the terminal position of the diene ligands furnishes fused bicyclo[3.3.0]octanone and bicyclo[4.3.0]nonanone derivatives after acid quenching. The iron-mediated intramolecular nucleophilic addition allows for the direct stereocontrol of four stereogenic centers of these fused bicyclic skeletons.