Arylation of diethyl alkylmalonates: synthetic route to diethyl alkyl(substituted aryl)malonates with the aid of temporary arene complexation by the cyclopentadienyliron moiety

Abstract

Nucleophilic substitution of chlorine in the ironcyclopentadienyl hexafluorophosphates of chlorobenzene, isomeric chlorotoluenes and dichlorobenzenes (1) with the anions generated from diethyl alkylmalonates (2) and (3) leads to the formation of ironcyclopentadienyl complexes of diethyl alkyl(substituted phenyl)malonates (4) and (5). An excess of the anion employed in reactions with the m- and p-dichlorobenzene complexes leads to substitution of both chlorine atoms and formation of isomeric phenylenedimalonate complexes (8). Malonyl cations (4) and (5) possessing a chloro substituent on the complexed phenyl ring provide the possibility of further modifications of phenyl ring substituents via substitution [complex (10)] or addition reactions [complexes (12)]. The described complexes have been demetallated giving diethyl alkyl(substituted phenyl)malonates in >50% overall yield from the cations (1). All the complexes and compounds have been fully characterized. This approach to the synthesis of the diethyl alkyl(substituted phenyl)malonates which are intermediates in the synthesis of important biologically active barbiturates is easy, efficient, and currently the most general in the area.