Synthesis of naphth[2,1-a]azulenes via [8 + 2] cycloaddition of 2Hcyclohepta[b]furan-2-ones, and their reactivity, optical, and structural properties

Abstract

A concise and efficient synthetic route to naphth[2,1-a]azulenes was developed via [8 + 2] cycloaddition of 2Hcyclohepta[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[2,1a]azulenes exhibited pronounced halochromic behaviour and fluorescence in acidic media. Electrochemical studies indicated predominantly irreversible redox behaviour, however, certain donor-acceptor systems displayed quasireversible responses attributed to slow electron transfer kinetics.

Supplementary files

Article information

Article type
Paper
Submitted
17 Sep 2025
Accepted
13 Oct 2025
First published
13 Oct 2025

Org. Biomol. Chem., 2025, Accepted Manuscript

Synthesis of naphth[2,1-a]azulenes via [8 + 2] cycloaddition of 2Hcyclohepta[b]furan-2-ones, and their reactivity, optical, and structural properties

T. Shoji, A. Yamazaki, M. Yoshida, M. Yasunami, T. Kamayachi, I. Uchiyama, S. Mori, T. Okujima, R. Sekiguchi and S. Ito, Org. Biomol. Chem., 2025, Accepted Manuscript , DOI: 10.1039/D5OB01492A

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