Evaluation of through-space interaction in [2.2]metacyclophanes by diazo coupling reaction

Abstract

An azobenzene moiety was introduced into various [2.2]metacyclophanes (MCPs)1via diazo coupling reactions. The functional groups on the inner (8,16–) or outer (13–) positions affect the reactivity of the outer (5–) position toward the diazonium salts to a large extent. It was also observed that one aromatic ring of [2.2] MCPs can be subject to attack of diazonium salts very easily; however, the other aromatic ring never undergoes attack. The electronic absorption wavelengths of the azo[2.2]MCPs are bathochromically shifted from those of model reference compounds. When the λ_max-values of azo[2.2]MCPs which carry a functional group on the outer (13–) position are plotted against the substituent's Hammett contstants (σ_ρ), a straight line is obtained. These results established that the electronic effect of the functional group is transmittable between the two aromatic rings in [2.2]MCPs by a through-space interaction.