Thermal isomerisation of 1-chloro-1-fluoro-2-vinylcyclopropanes: competition between the vinylcyclopropane–cyclopentene rearrangement and cyclopropyl–allyl transformation

The gas-phase pyrolysis of 1-chloro-1-fluoro-2-vinylcyclopropane and 1-chloro-1-fluoro-2-methyl-2-vinylcyclopropane at 305–360 °C afforded 4-chloro-4-fluorocyclopentenes and chlorofluorobutadienes as a result of competitive vinylcyclopropane–cyclopentene rearrangement and cyclopropyl–allyl isomerisation.