Tricarbonyl[(1−4-η)-2-Methoxy-5-methylenecyclohexa- 1,3-diene]iron as a Synthetic Intermediate:  Sequential Electrophilic and Nucleophilic Additions

Tricarbonyl[(1−4-η)-2-methoxy-5-methylenecyclohexa-1,3-diene]iron reacts with electrophiles to give the cyclohexadienylium−Fe(CO)₃ cation, which either reacts with nucleophiles to form a new quaternary center or undergoes competitive loss of an acidic α-proton to give a new triene complex. This constitutes a new reaction sequence for the synthesis of 4,4-disubstituted cyclohexen-2-ones with the simultaneous introduction of two functional groups.