Ferrocene compounds: XI. Synthesis and cyclization of some ferrocenecarboxylic acids

Abstract

The ferrocenecarboxylic acids FcCHC(CO 2H)(CH 2) 1–2CO 2H (Fc = ferrocenyl) were converted in good yields, under the conditions of the Clemmensen reduction, to the saturated products FcCH 2CH(CO 2H)(CH 2) 1–2CO 2H. The possible course of these reactions, via the corresponding δ- or γ-lactones, is discussed. By the action of trifluoroacetic anhydride (or acetic anhydride) these ferrocenecarboxylic acids were converted into the corresponding cyclic anhydrides. The intramolecular Friedel-Crafts reaction of α-ferrocenylmethylglutaric anhydride gave the heteroannularly cyclized product 1,1′-[β-(2-carboxyethyl)-α-oxotrimethylene]ferrocene, and under the same conditions α-ferrocenylmethylsuccinic anhydride was converted into the homoannularly cyclized cyclopentadienyl(4,5,6,7-tetrahydro-5-carboxy-7-oxoindenyl)iron.