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The Ring Closure of Cyclopenta-1, 3-dien-5-yl-carbene to Benzvalene. A mechanistic study of an unusual carbene reaction

Authors
Gandillon, Gérard
Published in Helvetica Chimica Acta. 1981, vol. 64, no. 3, p. 844-853
Abstract The base-induced a-elimination of hydrogen chloride from 5-chloromethyl-5-methylcyclopenta-1, 3-diene (19) produces 1-methyltricyclo [3.1.0.02,6]hexene-3 (1-methylbenzvalene) (21) together with toluene and spiro [4.2]heptadiene (23). A common intermediate, 5-methylcyclopenta-1, 3-dien-5-yl-carbene (20), accounts for these results by intramolecular 1, 4-carbene addition, 1, 2-carbon shift and CH-insertion, respectively. Independent synthesis of 2-methylbenzvalene (24) allows us to show that the classic intramolecular cyclopropanation is completely suppressed by the linear cheletropic ring closure. MINDO/3 predicts the key carbene to have a bisected conformation in its singlet ground state. This ideally fulfills the stereoelectronic conditions for a carbene reaction of least motion. The influence of the methyl substituent upon that process is discussed.
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BURGER, Ulrich, GANDILLON, Gérard, MAREDA, Jiri. The Ring Closure of Cyclopenta-1, 3-dien-5-yl-carbene to Benzvalene. A mechanistic study of an unusual carbene reaction. In: Helvetica Chimica Acta, 1981, vol. 64, n° 3, p. 844-853. https://archive-ouverte.unige.ch/unige:6214

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Deposited on : 2010-04-20

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