title: Synthesis of redox-active, intramolecular charge-transfer chromophores by the [2+2] cycloaddition of ethynylated 2H-cyclohepta[b]furan-2-ones with tetracyanoethylene.
abstract: Ethynylated 2H-cyclohepta[b]furan-2-ones 5-15 have been prepared by Pd-catalyzed alkynylation of 3-iodo-5-isopropyl-2H-cyclohepta[b]furan-2-one (2) with the corresponding ethynylarenes or the reaction of 2-iodothiophene with 3-ethynyl-5-isopropyl-2H-cyclohepta[b]furan-2-one (4) under Sonogashira-Hagihara conditions. Compounds 5-15 reacted with tetracyanoethylene in a formal [2+2] cycloaddition reaction, followed by ring opening of the initially formed [2+2] cycloadducts, cyclobutenes, to afford the corresponding 1,1,4,4-tetracyanobutadienyl (TCBD) chromophores 16-26 in excellent yields. The intramolecular charge-transfer interactions between the 2H-cyclohepta[b]furan-2-one ring and TCBD acceptor moiety were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behavior of the novel TCBD derivatives 16-26 was examined by cyclic voltammetry and differential pulse voltammetry, which revealed multistep electrochemical reduction properties, depending on the number of TCBD units in the molecule. Moreover, a significant color change was observed by UV/Vis spectroscopy under electrochemical reduction conditions.
authors: Department of Chemistry, Faculty of Science, Shinshu University, Matsumoto 390-8621, Japan. tshoji@shinshu-u.ac.jp
authors: Taku
authors: T
authors: Shoji
authors: Junya
authors: J
authors: Higashi
authors: Shunji
authors: S
authors: Ito
authors: Tetsuo
authors: T
authors: Okujima
authors: Masafumi
authors: M
authors: Yasunami
authors: Noboru
authors: N
authors: Morita