Cyclopropane chemistry. Part 4. The reactions of 1,2,2-trifluoroethylidene with alkenes and pyrolysis of the resulting cyclopropanes

Abstract

1,2,2-Trifluoroethylidene, generated by the pyrolysis of (1,1,2,2-tetrafluoroethyl)trifluorosilane, reacts with tetrafluoroethylene, ethylene, and a series of methyl-substituted ethylenes to give the corresponding 1-fluoro-1-di-fluoromethylcyclopropanes in good yield; cyclohexene gives the corresponding norcarane, and tris(trifluoromethyl)phosphine gives the corresponding phosphorane (CF₃)₃[graphic omitted]·[graphic omitted]F·CHF₂. Pyrolysis of 1,2,2,3,3-pentafluoro-1-difluoromethylcyclopropane affords difluorocarbene and 3H-pentafluoropropene, but pyrolysis of the methyl-substituted cyclopropanes results in the formation of dienes in high yield, e.g. the 1,4-dienes CHF:CF·CMeR·CMe:CH₂ from the cyclopropanes [graphic omitted]F·CHF₂(R = H or Me) or 1,3-dienes from the methyl-substituted cyclopropanes, e.g. [graphic omitted]F·CHF₂→ CH₂:CMe·C(CHF₂):CH₂. In certain cases further dehydrofluorination of the 1,3-dienes affords trienes, e.g. [graphic omitted]F·CHF₂→ CH₂:CMe·C(:CHF)·CMe:CH₂.