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Gas-Phase Kinetics of the Pyrolysis of Some 3,3-Dimethyl-1-(trimethylsilyl)-cyclopropenes - Unexpected Product Distribution in the Cyclopropene Rearrangement (1994)

Walsh, Robin ; Untiedt, Sven ; Meijere, Armin De

Weinheim : Wiley-Blackwell

Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 237-245

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ISSN: 0009-2940

Schlagwort(e): Cyclopropenes, 3,3-dimethyl-1-trimethylsilyl-substituted ; Cyclopropene, isomerisation ; Gas-phase kinetics ; Ring opening ; Diradical intermediates ; Cyclopropylidene intermediates ; Chemistry ; Inorganic Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The gas-phase pyrolyses of 1,3,3-trimethyl-2-(trimethylsilyl)-cyclopropene (9), 3,3-dimethyl-1,2-bis(trimethylsilyl)cyclopropeneTextReactantlog (A/s-1)Ea/kj mol-1(kcal mol-1)913.41 ± 0.22192.1 ± 2.5(45.9 ± 0.6)1013.54 ± 0.19184.4 ± 2.1(44.1 ± 0.5)1112.17 ± 0.38124.6 ± 3.1(29.8 ± 0.7)(10), and 3,3-dimethyl-1-(methylthio)-2-(trimethylsilyl)cyclopropene (11) have been studied, and the pressure-independent Arrhenius parameters listed in the table were obtained. All three rearrangements are homogeneous, first-order and unimolecular reactions. Rather surprisingly all reactions give the corresponding isomeric allenes as the main products. Amongst possible mechanisms discussed, 10 is proposed to react via a cyclopropylidene intermediate, whilst the results for 9 and 11 throw light on the relative importance of the diradical- and vinylcarbene-type intermediates produced by cyclopropene ring opening.

Zusätzliches Material: 3 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/cber.19941270134

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Digitale Medien

Michael Addition of Imines to Alkynylcarbene Complexes with Subsequent Intramolecular Cyclization - An Efficient Three-Step Synthesis of 2H-Pyrroles (1994)

Funke, Frank ; Duetsch, Michael ; Stein, Frank ; [weitere]

Weinheim : Wiley-Blackwell

Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 911-920

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ISSN: 0009-2940

Schlagwort(e): Chromium, [2-(methyleneamino)ethenyl]carbene complexes ; Michael addition of imines ; (1-alkynylcarbene)-chromium complexes ; 2H-Pyrroles ; Cyclization of {[2-(methyleneamino)ethenyl]carbene}chromium complexes ; Chemistry ; Inorganic Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: Imines 7, 11-13 were added to (1-alkynylcarbene)chromium complexes 6a-d to form {[2-(methyleneamino)ethenyl]-carbene}chromium complexes 8a-d, 14a-d, 15a-d, 16a-d in good to very good yields (63-98%) except for two cases (41-59%). The carbene ligands of the latter compounds cyclize to 2H-pyrroles 9a-d, 17a-d, 18a-d, 19a-d upon heating in tetrahydrofuran solution to 50-55°C.

Zusätzliches Material: 4 Tab.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/cber.19941270520

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Digitale Medien

Gas-Phase Kinetics of the Thermal 1-Alkoxy-1-vinylcyclopropane to 1-Alkoxy-1-cyclopentene Rearrangement (1991)

McGaffin, Gregory ; Meijere, Armin De ; Walsh, Robin

Weinheim : Wiley-Blackwell

Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 939-945

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ISSN: 0009-2940

Schlagwort(e): 1-Vinylcyclopropane ; 1-methoxy- ; 1-ethoxy- ; Vinylcyclopropane ; isomerization ; Gas-phase kinetics ; Ring expansion of 1-alkoxy-1-vinylcyclopropanes ; Diradical intermediates ; Chemistry ; Inorganic Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The title studies have been carried out with both 1-vinyl-1-cyclopropyl methyl ether (1-OMe) and 1-vinyl-1-cyclopropyl ethyl ether (1-OEt) in the temperature ranges 274.6-324.5 and 273.6 - 323.0°C, respectively. Both reactions predominantly give the vinylcyclopropane-cyclopentene (VCP-CP) rearrangement products 1-cyclopenten-1-yl methyl ether (2-OMe) and 1-cyclopenten-1-yl ethyl ether (2-OEt). Additionally, 2-OEt eliminates ethene (3) in a consecutive reaction at a lower reaction rate compared with the VCP-CP rearrangement. The rearrangements obey first-order kinetics and have been shown to be homogeneous, pressure-independent reactions with the following Arrhenius equations:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {1 - {\rm OMe:}} {{\rm lg}\left({k/s^{-1}} \right) = \left({13.89 \pm 0.23} \right) - \left({191.30 \pm 2.55{\rm kJ mol}^{-1}} \right)/RT\ln 10} \\\end{array} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {1 - {\rm OMt:}} {{\rm lg}\left({k/s^{-1}} \right) = \left({13.77 \pm 0.01} \right) - \left({188.80 \pm 1.85{\rm kJ mol}^{-1}} \right)/RT\ln 10} \\\end{array} $$\end{document}The Arrhenius parameters represent reliable values for general 1-vinyl-1-cyclopropyl alkyl ether→1-cyclopenten-1-yl-alkyl ether (1-OR→2-OR) rearrangements within a large temperature interval in the gas phase. The results support a mechanism proceeding via a diradical. The stabilizing effect of methoxy substitution is discussed.

Zusätzliches Material: 2 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/cber.19911240439

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