Synthesis of novel 1,3,5-tris(arylazo)benzenes via Pd-catalyzed couplings and Cu(I)-mediated direct oxidations

A series of novel 1,3,5-tris-azobenzenes were prepared from 1,3,5-trihalobenzene via Pd-catalyzed couplings of N-Boc aryl hydrazines and subsequent Cu(I)-mediated direct oxidations. The oxidation of tris-arylhydrazide provided the azobenzene as a mixture of all four of the possible E/Z-isomers; [E,E,E]-, [E,E,Z]-, [E,Z,Z]-, and [Z,Z,Z]-1,3,5-tris-azobenzenes. A slow removal of the solvent in the dark transformed the isomers into the all-trans, [E,E,E]-isomer.