Synthesis of 2-aminofuran derivatives with azulene or N,N-dimethylanilino substituent was established by the formal [2 + 2] cycloaddition-retroelectrocyclization of 3-(1-azulenyl or N,N-dimethylanilino)-2-propyn-1-ols with tetracyanoethylene, followed by the intramolecular nucleophilic addition to the initially formed tetracyanobutadiene moiety of the internal hydroxyl group that come from 2-propyn-1-ol. The reaction proceeds under mild conditions with short reaction period. The products of the reaction are readily available with simple purification procedure. 2-Aminofuran derivatives obtained by this reaction were revealed to be convertible to 6-aminofulvene derivatives with the treatment of various amines. The structure of 2-aminofuran and 6-aminopentafulvene with N,N-dimethylanilino substituent was confirmed by single crystal X-ray structural analysis.
Abstract:Tris[(3-phenyl-1-azulenyl)tetracyanobutadiene]s and tris(aryltetracyanobutadiene)s connected to a 1,3,5-tri(1-azulenyl)benzene core (tris-AzTCBDs) have been prepared by the Pd-catalyzed alkynylation of tris(3-iodo-1-azulenyl)benzene derivative with the corresponding 1-ethynylazulene or ethynylbenzene derivatives under SonogashiraHagihara cross-coupling conditions, followed by the reaction with tetracyanoethylene (TCNE) in a formal [2 + 2] cycloadditionretroelectrocyclization (CA-RE) reaction. The intramolecular charge-transfer (ICT) interactions of the new chromophores were investigated by the comparison with those of the model tetracyanobutadiene derivatives with azulene substituents (AzTCBDs), which were prepared by the reaction of the corresponding 1-ethynylazulene derivative with iodoarenes, followed by the CA-RE reaction with TCNE, utilizing UV/Vis spectroscopy and theoretical calculations. The redox behavior of the alkyne precursors and the tetracyanobutadiene derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties. Moreover, significant color changes of these compounds were observed by visible spectroscopy under the electrochemical reduction conditions.
Azulene-substituted tetracyanobutadienes (AzTCBDs) and dicyanoquinodimethanes (AzDCNQs) connected with naphthalene cores were prepared by the reaction of 1-azulenylalkynes with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a formal [2 + 2] cycloaddition-retroelectrocyclization. The characteristic intramolecular charge transfer (ICT) characters were investigated by using UV/Vis spectroscopy and theoretical calculation. The redox behaviors of AzTCBDs and AzDCNQs were examined by cyclic voltammetry and differential pulse voltammetry, which revealed their properties of multi-electron transfer depending on the number of AzTCBD and AzDCNQ moieties. Moreover, significant color changes were observed by visible spectroscopy under the electrochemical reduction conditions.
Tris(1‐azulenylacetylene) and tris(1‐azulenylethynylarylacetylene) chromophores connected to a 1,3,5‐tri(1‐azulenyl)benzene core have been prepared by the Pd‐catalyzed alkynylations of 1‐ethynylazulene with tris(3‐iodo‐1‐azulenyl)benzene or iodoarene derivatives substituted with a 1‐azulenylethynyl group with tris(3‐ethynyl‐1‐azulenyl)benzene under Sonogashira–Hagihara cross‐coupling conditions. These compounds reacted with tetracyanoethylene in formal [2+2] cycloaddition–retroelectrocyclization reactions to afford the corresponding tris(1‐azulenyltetracyanobutadiene) and tris[1‐azulenylbis(tetracyanobutadiene)] chromophores in excellent yields. The redox behavior of the tetracyanobutadiene (TCBD) derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties. Moreover, significant color changes were observed by visible spectroscopy under the electrochemical reduction conditions.
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