Diels–Alder approach to the synthesis of azulene-substituted benzene derivatives. Synthesis and redox behavior of 1,2-di(6-azulenyl)tetraphenylbenzenes

1,2-Di(6-azulenyl)tetraphenylbenzenes and (6-azulenyl)pentaphenylbenzenes were synthesized by Diels–Alder reaction of di(6-azulenyl)acetylenes and 6-(phenylethynyl)azulenes with tetraphenylcyclopentadienone. Mono(6-azulenyl)benzenes exhibited a reduction wave upon cyclic voltammetry (CV). In contrast to the benzene derivatives, di(6-azulenyl)benzenes showed a two-step reduction wave at similar potential region upon CV, which revealed the formation of dianions stabilized by 6-azulenyl substituents under electrochemical reduction conditions.