Synthesis of 2‑Amino-4-arylazulenes\nfrom 8‑Aryl‑2<i>H</i>‑cyclohepta[<i>b</i>]furan-2-ones and\nTransformation into 6‑Aryl‑7<i>H</i>‑naphth[3,2,1-<i>cd</i>]azulen-7-ones

2-Amino-4-arylazulene derivatives\nwere prepared from 8-aryl-2<i>H</i>-cyclohepta[<i>b</i>]furan-2-ones, which were\nconverted into 6-aryl-7<i>H</i>-naphth[3,2,1-<i>cd</i>]azulen-7-ones through a several step process. The reaction of 8-aryl-2<i>H</i>-cyclohepta[<i>b</i>]furan-2-ones bearing an\nester group at the 3-position with malononitrile in the presence of\ntriethylamine afforded 2-amino-4-arylazulenes. The prepared 2-amino-4-arylazulenes\nwere converted to the corresponding 2-chloro derivatives by the Sandmeyer\nreaction, which were subsequently transformed into 2,4-diarylazulenes\nby Suzuki–Miyaura coupling with various aryl boronic acids.\n2,4-Diarylazulenes underwent intramolecular cyclization between aryl\nand cyano groups by Brønsted acid to give 6-aryl-7<i>H</i>-naphth[3,2,1-<i>cd</i>]azulen-7-ones. UV/vis spectral\nanalysis revealed that 6-aryl-7<i>H</i>-naphth[3,2,1-<i>cd</i>]azulen-7-one with a <i>N</i>,<i>N</i>-dimethylaminophenyl group at the 6-position exhibited a broad and\nstrong absorption band in the visible region due to intramolecular\ncharge transfer. Furthermore, 6-aryl-7<i>H</i>-naphth[3,2,1-<i>cd</i>]azulen-7-ones exhibited halochromism in 30% CF<sub>3</sub>CO<sub>2</sub>H/CH<sub>2</sub>Cl<sub>2</sub>. Although fluorescence\nwas not observed in solution, 8-aryl-2<i>H</i>-cyclohepta[<i>b</i>]furan-2-ones with an ester function were found to fluoresce\nin the solid state. 6-Aryl-7<i>H</i>-naphth[3,2,1-<i>cd</i>]azulen-7-ones also displayed spectral changes with good\nreversibility under the electrochemical redox conditions.