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Updated: Jan 15, 2026

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
Synthesis of naphth[2,1-a]azulenes via [8 + 2] cycloaddition of 2H-cyclohepta[b]furan-2-ones, and their reactivity,
Taku Shoji1, Akari Yamazaki2, Miku Yoshida1
1Department of Chemical Biology and Applied Chemistry, College of Engineering, Nihon University, Koriyama 963-8642, Fukushima, Japan. shoji.taku@nihon-u.ac.jp.
Abstract:
A concise and efficient synthetic route to naphth[2,1-a]azulenes was developed via [8 + 2] cycloaddition of 2H-cyclohepta[b]furan-2-ones with enamines or a silyl enol ether derived from α-tetralones. A diverse array of functionalized naphth[2,1-a]azulenes was further obtained through functionalization reactions, including electrophilic substitution, homocoupling, and cross-coupling reactions. Comprehensive spectroscopic analyses, including 1H NMR, UV-Vis, fluorescence spectroscopy, and single-crystal X-ray diffraction, along with NICS calculations, revealed reduced aromaticity of the azulene core and a strong dependence of optical properties on the substitution pattern. Furthermore, naphth[2,1-a]azulenes exhibited pronounced halochromic behaviour and fluorescence in acidic media. Electrochemical studies indicated predominantly irreversible redox behaviour, however, certain donor-acceptor systems displayed quasi-reversible responses attributed to slow electron transfer kinetics.
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