Formation of Azulene‐embedded Nanographene via Unusual Naphthalene to Azulene Rearrangement During Scholl Reaction

Incorporation of a non-hexagonal ring into a nanographene framework can bring up with new electronic properties. During our attempted synthesis of naphthalene-bridged double [6]helicene and heptagon-containing nanographene by Scholl reaction, an unexpected azulene-embedded nanographene ( 1a ) and its triflyloxylated product ( 1b ) were obtained, which were confirmed by X-ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring fused substructure containing two formal azulene units is formed, but only one of them shows azulene-like electronic structure. The formation of this unique structure can be explained by arenium ion mediated 1,2-phenyl migration and a naphthalene to azulene rearrangement reaction according to our in-silico study. This report represents the first experimental example of thermodynamically unfavorable naphthalene to azulene rearrangement and may open the opportunity to new azulene-based molecular materials.