Tricyclic Quinazoline Alkaloids Conjugated to Ferrocene: Synthesis, Structure, and Redox Behavior of Ferrocenylmethylene-Substituted 7H-Deoxyvasicinones

The first organometallic derivatives of tricyclic quinazoline derivatives are prepared by condensation of the active C-3 methylene group of 7H-deoxyvasicinones with ferrocenecarbaldehyde. By following this route the conjugated parent alkaloid and derivatives with nitro, amino, as well as some alkanoylamino groups at C-7 were attached at the ferrocene moiety, thereby significantly extending the system. In addition, the parent compound was subjected to the reaction by treatment with ferrocene-1,1-dicarbaldehyde, giving rise to the double condensation product, which is only the second case of a 1,1-disubstituted ferrocene derivative with two alkaloid substituents. A number of the compounds obtained were subjected to X-ray crystallographic analyses. In all cases, the substituents adopt a coplanar conformation with the ferrocene cyclopentadienyl ligands. The influence of the substituents at C-7 through the extended conjugated system on the iron atom is reflected by results of cyclic voltammetric measurements as well as by DFT calculations.