Preparation and characterization of 16‐benzoylated tetraaza[14]annulenes

The condensation reaction between tetraaza[14]annulene (1) and a series of para‐substituted benzoyl chlorides led to the 16‐benzoylated corresponding products in 13–21% yields, but 1 was unreactive with alkyl acid chlorides and easily cleaved in macrocyclic framework. The mass spectra show the presence of molecular ion peaks which support the 16‐benzoylated products. A strong ir band due to the C = N stretching mode of the macrocyclic moiety was observed at 1610 cm−1 and shifted slightly toward higher energy upon benzoylation. An intense ir band which was associated with a C = 0 stretching mode was newly observed at 1640 cm1. The very strong absorption band about 29000 cm−1 was attributed to the π − π* transition and gave a slight shift to higher frequency on benzoylation. All proton signals except for methyl protons exhibit downfield shifts due to the deshielding effect of the substituted benzene ring, but the methyl proton peaks show upfield shifts due to the shielding effect caused by the magnetic anisotropy of the substituted benzene ring. The 13C nmr result is also in accord with that of 1H nmr.