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.

Synthesis of donor–acceptor chromophores by the [2 + 2] cycloaddition of arylethynyl-2H-cyclohepta[b]furan-2-ones with 7,7,8,8-tetracyanoquinodimethane

“…We have reported the synthesis of redox-active chromophores 15 with the aim of the creation of stabilized electrochromic materials. 17 As a part of this study, we have also reported 2H-cyclohepta [b]furan-2-one-substituted TCBDs 13 and azulenesubstituted TCBDs 10 and DCNQs 11 , in which we identified some novel hybrid structures of violenes and cyanines 18 with the redox 20 activities. Bis(2H-cyclohepta [b]furan-2-one-substituted) and bis(azulene-substituted) TCBDs, which exhibit reversible color changes during the electrochemical reaction, are successful examples of an extension for the violene-violene hybrid structure.…”

“…The shift value of 10 (27 nm) is larger than that of the corresponding TCNE-adduct of 1 (6 nm). 13 These results are assumed that the first excited-state has a larger dipole moment 35 compared with that in the ground state, due to the effective ICT character from 2H-cyclohepta [b]furan-2-one to the DCNQ unit.…”

“…13 To the synthesis of the novel 15 DCNQ derivatives, the [2+2] cycloaddition-cycloreversion sequence was applied to the acetylene derivatives 1-9 with TCNQ under the conditions described in the literature. 6,11 Thus, the reaction of 1 with TCNQ in refluxing ethyl acetate afforded 10 in 91% yield as a sole product (Scheme 1).…”

“…13 The study revealed the TCBD derivatives are featured by a strong ICT absorption in their UV/Vis spectra, which is characterized by time-dependent density functional theory (TD-70 DFT) calculations. Reaction of arylethynyl-2H-cyclohepta [b]furan-2-ones 1-9 with TCNQ is expected to show high reactivity toward the formal [2+2] cycloadditioncycloreversion sequence to afford the novel DCNQ derivatives.…”

Synthesis, Properties, and Crystal Structure of DDQ-Adducts of Ethynylated 2H-Cyclohepta[b]furan-2-ones

“…5 Although its unusual reactivity has already been revealed by many research groups, 6 there are few 2H-cyclohepta [b]furan-2-one derivatives for the application to the advanced materials with potentially useful electronic properties. For the extension of this chemistry, we have focused our studies on the synthesis of tetracyanobutadiene (TCBD) 7 and dicyanoquinodimethane (DCNQ) 8 derivatives of 2H-cyclohepta[b]furan-2-one by the formal [2+2] cycloaddition-cycloreversion reaction of the corresponding alkyne derivatives with tetracyanoethylene (TCNE) and 7,7,8,8- The electronic properties of the new compounds obtained by this reaction were characterized by CV, DPV, and absorption spectroscopy. In addition one of the DDQ-adducts was revealed the molecular structure by X-ray crystallographic analysis.…”