Sigmatropic Isomerization of Tetraphenylcyclopentadienes: Reaction Mechanism and Quantum Chemical Treatment

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Title:Sigmatropic Isomerization of Tetraphenylcyclopentadienes: Reaction Mechanism and Quantum Chemical Treatment
Creators:
Šebek, Pavel
Sedmera, Petr
Böhm, Stanislav
Kuthan, Josef
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 58, 4, pp. 882-892

Abstract

Thermal isomerization of 2,3,5,5-tetraphenylcyclopenta-1,3-diene (<i>Ia</i>) or 1,2,4,5-tetraphenylcyclopenta-1,3-diene (<i>IIa</i>) in melts lead to identical equilibrium mixtures of hydrocarbon <i>IIa</i> with prevailing 1,2,3,4-tetraphenylcyclopenta-1,3-diene (<i>IIIa</i>). The isomerization of bis-tert-butyl cyclopentadienes <i>Ib</i> or <i>Ic</i> produces an equilibrium mixture with preponderant 1,2,3,4-tetrasubstituted cyclopentadienes <i>IIIb, IIIc</i> besides minority isomers <i>IIb, IIc</i>. On the contrary, the 1,2,4,5-tetrasubstituted phenanthrene hydrocarbon <i>IXa</i> having forced coplanarity of both benzene rings only partially isomerizes to <i>IXb</i>. Equilibrium constants of the isomerization <i>IIa</i> → <i>IIIa</i> in diphenyl ether at 323 to 433 K were measured (<i>K</i> = 5.8 -2.3). Relative stability of hydrocarbons <i>Ia, IIa, IIIa</i> and <i>VIIa</i> is interpreted on the basis of quantum chemical AM1 calculations. The time course of isomerization of the hydrocarbon <i>IIc</i> allowed us to propose two reaction mechanisms based on the [1,3]- and [1,5]-sigmatropic steps. The preparation of 2,3,5,5-tetrasubstituted cyclopentadienes <i>Ia - Ic</i> by dehydration of <i>cis</i>-1,2-diols <i>IVa - IVc</i> is described.

Title:Sigmatropic Isomerization of Tetraphenylcyclopentadienes: Reaction Mechanism and Quantum Chemical Treatment
Creators:
Šebek, Pavel
Sedmera, Petr
Böhm, Stanislav
Kuthan, Josef
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:58
Number:4
Page Range:pp. 882-892
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc19930882UNSPECIFIED
ID Code:205
Item Type:Article
Deposited On:06 Feb 2009 16:59
Last Modified:06 Feb 2009 15:59

Citation

Šebek, Pavel; Sedmera, Petr; Böhm, Stanislav; Kuthan, Josef (1993) Sigmatropic Isomerization of Tetraphenylcyclopentadienes: Reaction Mechanism and Quantum Chemical Treatment. Collection of Czechoslovak Chemical Communications, 58 (4). pp. 882-892. ISSN 0010-0765

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