The preparation and properties of polyfluoro aromatic and heteroaromatic compounds

This review is concerned with ring systems formally recognised as "aromatic" and possessing a large proportion of fluorine atoms directly attached to the carbon skeleton. These include derivatives of the following: benzene and polynuclear benzenoid systems; pyridine, diaza-and triazabenzenes and some of their fused six-membered ring compounds; and a wide variety of fused ring carbocycles and heterocycles. Some highly fluorinated non-benzenoid aromatic compounds obeying the Huckel 4n + 2 pi electron rule, as well as antiaromatic 4n pi electron systems, are included in the survey. The wide variety of methods used for synthesising these highly fluorinated compounds, which enabled them to be regarded no longer as mere chemical curiosities, is presented. The chemical behaviour of polyfluoro aromatic and heteroaromatic compounds, at the fluorinated ring, forms the major proportion of this review: reactions with nucleophiles and a rationalisation of orientation reactions; reactions with electrophiles, free radicals, carbenes and nitrenes; the formation of stable salts of radical cations; photochemical reactions and the formation of valence isomers; and rearrangement reactions. Organometallic derivatives of polyfluorinated compounds have been extensively used in organic synthesis. (C) 1997 Elsevier Science S.A.