Synthesis of 2-azulenyl-1,1,4,4-tetracyano-3-ferrocenyl-1,3-butadienes by [2+2] cycloaddition of (Ferrocenylethynyl)azulenes with tetracyanoethylene

摘要

1-, 2-, and 6-(Ferrocenylethynyl)azulene derivatives 10-16 have been prepared by palladium-catalyzed alkynylation of ethynylferrocene with the corresponding haloazulenes under Sonogashira-Hagihara conditions. Compounds 10-16 reacted with tetracyanoethylene (TCNE) in a [2+2] cycloaddition- cycloreversion reaction to afford the corresponding 2-azulenyl-1,1,4,4,- tetracyano-3-ferrocenyl-1,3-butadiene chromophores 17-23 in excellent yields. The redox behavior of the novel azulene chromophores 17-23 was examined by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions. Colorful chemistry: 1-, 2-, and 6-(ferrocenylethynyl)azulenes have been prepared by Sonogashira-Hagihara reaction of ethynylferrocene with the corresponding haloazulenes (see scheme). These ethynylazulene derivatives react with tetracyanoethylene in a [2+2] cycloaddition-cycloreversion reaction to afford the corresponding azulene chromophores in excellent yields. Significant color change of the novel 1,1,4,4-tetracyano-1,3-butadiene (TCBD) derivatives was observed by visible spectroscopy under electrochemical reduction conditions.