Synthesis, Properties, and Redox Behavior of Mono‐, Bis‐, and Tris[1,1,4,4,‐tetracyano‐2‐(1‐azulenyl)‐3‐butadienyl] Chromophores Binding with Benzene and Thiophene Cores

Abstract

Mono-, bis-, tris-, and tetrakis(1-azulenylethynyl)benzene and mono- and bis(1-azulenylethynyl)thiophene derivatives 5-10 have been prepared by Pd-catalyzed alkynylation of ethynyl arenes with 1-iodoazulene derivative or the 1-ethynylazulene derivative with tetraiodobenzene and iodothiophenes under Sonogashira-Hagihara conditions. Compounds 5-10 reacted with tetracyanoethylene in a [2+2] cycloaddition reaction to afford the corresponding 1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-3-butadienyl chromophores 12-16 in excellent yields, except for the reaction of the tetrakis(1-azulenylethynyl)benzene derivative. 1,1,4,4,-Tetracyano-2,3-bis(1-azulenyl)butadiene (17) was also prepared by the similar reaction of bis(1-azulenyl)acetylene (11) with tetracyanoethylene (TCNE). The redox behavior of novel azulene derivatives 12-17 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed multistep electrochemical reduction properties. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.

Reactions between 1‐Ethynylazulenes and 7,7,8,8‐Tetracyanoquinodimethane (TCNQ): Preparation, Properties, and Redox Behavior of Novel Azulene‐Substituted Redox‐Active Chromophores

“…Likewise, treatment of 4 with TCNE afforded 10 in 88 % yield, along with 14 [5] in 5 % yield (Scheme 3). The resulting mono adduct 10 was treated with TCNQ to give the TCNE/ TCNQ double adduct 12, with a thiophene core, in 85 % yield.…”

“…Treatment of 3 with TCNE gave the mono adduct 9 in 88 % yield, along with 13 [5] in 4 % yield (Scheme 3). [7] The synthesis of the TCNE/TCNQ double adduct 11 was achieved in 84 % yield by treatment of 9 with TCNQ (Scheme 3).…”

“…[5] The novel redox-active chromophores 5-8 were then obtained through [2+2] cycloaddition/cycloreversion reactions between 1-4 and TCNQ, as in the procedure reported by Diederich et al…”

“…[4] Recently we have reported reactions between tetracyanoethylene (TCNE) and mono-, bis-, and tris[2-(azulen-1-yl)ethynyl]benzene and -thiophene derivatives, giving the corresponding [1,1,4,4-tetracyano-2-(azulen-1-yl)-3-butadienyl] chromophores. [5] These new chromophores exhibit multistep reduction waves upon cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Moreover, significant multistep color changes are also observed on their electrochemical reduction.…”

Electrophilic ipso‐Substitution and Some Unique Reaction Behavior of 1,3,6‐Tri‐tert‐butylazulene

“…[22] In the case of azulene derivatives, we have also reported that 1,1,4,4-tetracyano-2,3-bis[5-isopropyl-3-(methoxycarbonyl)-1-azulenyl]butadiene showed solvatochromism. [23] We examined the solvatochromic effect of 12 in eight solvents, and the solvent dependence of the absorpwww.eurjoc.org Figure 4. ORTEP drawing of the molecular structure of 13.…”