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Note | Special issue | Vol 74, No. 1, 2007, pp.951-960
Published online, 20th September, 2007
DOI: 10.3987/COM-07-S(W)17
Synthesis of 4-(Azuleno[b]indolyl)-3-buten-2-ones by Intramolecular Tropylium Ion-Mediated Furan Ring-Unravelled Reaction

Mitsuko Nishiura, Ikuko Ueda, and Kimiaki Yamamura*

*Department of Chemistry, Faculty of Science, Kobe University, Nada-Ku, Kobe 6557-8501, Japan


4-(1-Benzenesulfonyl-6-azuleno[1,2-b]indolyl)-3-buten-2-one (1) and 4-(1-benzenesulfonyl-11-azuleno[2,1-b]indolyl)-3-buten-2-one (2) were synthesized from 1-benzenesulfonyl-3-(5-methylfuryl)-2-tropylioindole (10) and 1-benzenesulfonyl-2-(5-methylfuryl)-3-tropylioindole (14), respectively. The synthetic method is based on furan ring-unraveled reaction by the intramolecular electrophilic attack of the tropylium ion. 4-(6-Azuleno[1,2-b]indolyl)-3-buten- 2-one (3) and 4-(11-azuleno[2,1-b]indolyl)-3-buten-2-one (4) could be easily obtained from 1 and 2, respectively. Treatment of 3 and 4 with iodomethane gave N-methyl derivatives, 4-(1-methyl-6-azuleno[1,2-b]indolyl)-3-buten-2-one (5) and 4-(1-methyl-11-azuleno[2,1-b]indolyl)-3-buten-2-one (6), respectively, in moderated yield. The compounds, 1, 2, 3, 4, 5, and 6, which include the novel tetracyclic π conjugated azulene nuclei, are the azuleno[b]indole analogues of benzalacetone.