Cyclopentanones from Nucleophilic Addition/Carbonylation to (η⁴-Diene)Fe(CO)₃ Complexes

The addition of carbon nucleophiles to (1,3-diene)lron tricarbonyl complexes produces (homoallyl)Fe-(CO)₃ anionic complexes; as reported earlier, CO is incorporated at 1.5 atm to give acyliron anionic complexes. With most open-chain 1,3-diene ligands, further cyclization occurs, producing cyclopentanone derivatives with the anionic substituent in the 3-position. The yields are good if the nucleophiles are sufficiently reactive, while the primary limitation is the resistance to ring closure with multiply substituted dienes. With 2-substituted 1,3-dienes, the cyclopentanone product is formed with a specific cis relationship of the substitutents at C-3 and C-4. Through deuterium labeling studies, a mechanism involving β-hydride elimination/readdition is demonstrated as the final stage of the cyclopentanone formation.