Novel synthesis of benzalacetone analogues of naphth[a]azulenes by intramolecular tropylium ion-mediated furan ring-opening reaction and X-ray investigation of a naphth[1,2-a]azulene derivative |
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Authors: | Yamamura Kimiaki Kawabata Shizuka Kimura Takatomo Eda Kazuo Hashimoto Masao |
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Institution: | Department of Chemistry, Faculty of Science, Kobe University, Rokkodai, Nada, Japan. kyama@kobe-u.ac.jp |
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Abstract: | reaction: see text] Benzalacetone analogues of naphth1,2-a]azulene (8), naphth2,1-a]azulene (13), and naphth2,3-a]azulene (18) were synthesized from 2-(5-methyl-2-furyl)-1-tropylionaphthalene (7), 1-(5-methyl-2-furyl)-2-tropylionaphthalene (12), and 2-(5-methy-2-furyl)-3-tropylionaphthalene (17), respectively. The synthetic method is based on furan ring-opening reaction by the intramolecular electrophilic attack of a tropylium ion. Single-crystal X-ray work on the naphth1,2-a]azulene derivative (8) revealed that its tetracyclic system exhibited deformation from planarity similar to that of benzoc]phenanthrene (tetrahelicene). A centrosymmetric associated dimer structure, just like the molecules of carboxylic acids but via C=O...H-C hydrogen bonds, was found in the crystal. Reduction of bond-length alternation in the seven-membered ring was also found. |
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