Preparation and reactions of methoxycarbonyl-substituted cycloheptadienyliron tricarbonyl cations: unusual regiochemistry during the addition of stabilized enolate nucleophiles

Abstract

Tricarbonyl(1-methoxycarbonylcycloheptadienyl)iron hexafluorophosphate (9) and tricarbonyl(3-methoxycarbonylcycloheptadienyl)iron hexafluorophosphate (12) were prepared and thier reactions with a range of nucleophiles were examined. Cyanide, borohydride, and malonate enolate all added exclusively to C-2 of (9) and predominantly to C-2 of (12), while Me₂CuLi, hydroxide, and potassium phthalimide all reacted at C-1 of both complexes. The unusual regioselectivity during additions of NaCH(CO₂Me)₂ reflects a considerable perturbation of the dienyl–Fe system by the ester substituent.