Synthesis and Reactivity of Difluoroaromatic Compounds Containing Heterocyclic Central Groups

The reaction of trichloroacetaldehyde with fluorobenzene, followed by a series of transformations, gave 4-fluorobenzil and 4,4'-difluorobenzil which were used in the synthesis of new difluoroaromatic compounds with a heterocyclic central group. The 1H, 13C, and 19F NMR spectra of the newly synthesized difluoroaromatic compounds were studied. The charge densities on the carbon atoms attached to fluorine were calculated in terms of the PM3 and AM1 semiempirical approximations. A correlation was found between the charge on C(F) and the corresponding 13C and 19F chemical shifts. Using this correlation, the reactivity of difluoroaromatic compounds in nucleophilic substitution reactions was estimated.