Synthesis, molecular structure, electrochemistry and DFT study of a ferrocenyl-substituted 4-quinazolinone and related heterocycles

Abstract

2-Ferrocenyl-4(3H)-quinazolinone (2) was obtained by acylation of 2-aminobenzoic amide with ferrocenecarbonyl chloride (FcCOCl) and subsequent base-catalysed cyclisation of the intermediate 2-(ferrocenecarboxamido)benzamide (1). The related benzoxazin-4-one (4) was obtained analogously (though in one step) from FcCOCl and 2-aminobenzoic acid. Compounds 2 and 4 were thionated with P₂S₅ to give the corresponding ferrocenylated 4(3H)-quinazoline thione (3), and a mixture of benzothiazine-4-thione (5) and benzothiazine-4-one (6, major), respectively. Attempts to prepare 3-amino-2-ferrocenyl-4(3H)-quinazolinone from 4 and hydrazine hydrate failed. The reaction gave only 2-(ferrocenecarboxamido)benzohydrazide (7), which reacted with 2-chloro-1,3-dimethylimidazolidinium chloride to afford a mixture of cyclic and open (major) condensation products, both bearing the 1,3-dimethylimidazolidin-2-ylidene terminal group (8 and 9). All compounds were characterised by spectroscopic methods and the molecular structures of 1–7 and 9 were determined by X-ray diffraction analysis. Cyclic voltammetric measurements revealed that the compounds undergo a single one-electron oxidation, localised presumably at the ferrocene unit. DFT computations for 2 as a representative example performed in the gas phase and crystal state, reproduced well the experimental geometry and further supported the assignment of the redox processes.