A novel approach to the formation of quaternary centres and the introduction of angular substituents by using tricarbonyldieneiron complexes

Tricarbonyl-(4-methoxy-1-methylcyclohexadienylium)iron hexafluorophosphate (2) undergoes exclusive addition of carbanions derived from 1,3-dicarbonyl compounds at the methylated ring position. The directing effect of the methoxy-substituent in the cation of (2) has been applied successfully to the bicyclic analogues tricarbonyl-1,3–6-η-4-methoxybicyclo[4.4.0]deca-3,5-dienylium)iron hexafluorophosphate (8), and tricarbonyl-(1,3-6-η-4-methoxybicyclo[4.3.0]nona-3,5-dienylium)iron hexafluorophosphate (17), reactions of which with similar carbanions provide an efficient method of introduction of angular substituents.