Synthetic studies with iron carbonyl complexes. Versatile synthesis of olefinic side-chains to a tricarbonyl(cyclohexadiene)iron(0) ring

Tricarbonyl(cyclohexadiene)iron(0) complexes bearing olefinic side-chains at the 2- or the 5-position have been prepared by a versatile route. Terminal olefins are isomerised to internal isomers. The presence of a methoxy substituent at the 2-position prevents isomerisation of the coordinated diene into conjugation with the olefin, so locking the side-chain at the 5-exo-position.