Gas‐Phase Kinetics of the Thermal 1‐Alkoxy‐1‐vinylcyclopropane to 1‐Alkoxy‐1‐cyclopentene Rearrangement

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.