Partially Fluorinated Tetraazaacenes by Nucleophilic Aromatic Substitution

We report the sodium
hydride-mediated reactions of a diethynylated
diaminophenazine with perfluorobenzene, perfluoronaphthalene, and
two octafluoroanthracene derivatives. In all of the cases, an N,N-dihydropyrazine ring is formed, and
partially fluorinated tetraazapentacenes, tetraazahexacenes, and tetraazaheptacenes
(in their respective N,N-dihydro
forms) are easily prepared. In the case of the dihydrotetraazapentacenes
and -hexacenes, oxidation with manganese dioxide is possible to give
the desired, fully unsaturated tetraazaacenes; two molecules of the
azahexacene undergo a Diels–Alder reaction in which an alkyne
substituent in the conserved hexacene unit works as the dienophile
while the tetraazahexacene participates as the diene to give an unsymmetrical
dimer. All of the coupling targets were investigated by NMR and UV–vis
spectroscopies, and several single-crystal structures of the N,N-dihydrotetraazaacenes and also that
of the tetrafluorotetraazaacene were obtained.