Synthesis of 2-Amino-4-arylazulenes from 8-Aryl-2 H -cyclohepta[ b ]furan-2-ones and Transformation into 6-Aryl-7 H -naphth[3,2,1- cd ]azulen-7-ones

2-Amino-4-arylazulene derivatives were prepared from 8-aryl-2 -cyclohepta[ ]furan-2-ones, which were converted into 6-aryl-7 -naphth[3,2,1- ]azulen-7-ones through a several step process. The reaction of 8-aryl-2 -cyclohepta[ ]furan-2-ones bearing an ester group at the 3-position with malononitrile in the presence of triethylamine afforded 2-amino-4-arylazulenes. The prepared 2-amino-4-arylazulenes were converted to the corresponding 2-chloro derivatives by the Sandmeyer reaction, which were subsequently transformed into 2,4-diarylazulenes by Suzuki-Miyaura coupling with various aryl boronic acids. 2,4-Diarylazulenes underwent intramolecular cyclization between aryl and cyano groups by Brønsted acid to give 6-aryl-7 -naphth[3,2,1- ]azulen-7-ones. UV/vis spectral analysis revealed that 6-aryl-7 -naphth[3,2,1- ]azulen-7-one with a , -dimethylaminophenyl group at the 6-position exhibited a broad and strong absorption band in the visible region due to intramolecular charge transfer. Furthermore, 6-aryl-7 -naphth[3,2,1- ]azulen-7-ones exhibited halochromism in 30% CF CO H/CH Cl . Although fluorescence was not observed in solution, 8-aryl-2 -cyclohepta[ ]furan-2-ones with an ester function were found to fluoresce in the solid state. 6-Aryl-7 -naphth[3,2,1- ]azulen-7-ones also displayed spectral changes with good reversibility under the electrochemical redox conditions.