Cyclopropane chemistry. Part II. Cyclopropanes as sources of difluorocarbene

Abstract

The reactions of tetrafluoroethylene, chlorotrifluoroethylene, and 1,1 -dichlorodifluoroethylene with dichlorocarbene [generated from trifluoro(trichloromethyl)silane], and of the first two olefins with difluorocarbene (from difluorotristrifluoromethylphosphorane), under conditions which give good yields of the corresponding polyhalo-genocyclopropanes, are described. 1,1,2,2-Tetrafluorocyclopropane is obtained in only low yield from 1,1 -difluoro-ethylene and difluorotristrifluoromethylphosphorane. but is conveniently obtained (98% yield) by reduction, of 1,1-dichlorotetrafluorocyclopropane with tributylstannane. Evidence that some of the Cyclopropanes undergo a ‘chemically activated’ decomposition to difluorocarbene and an olefin following their formation is presented, and thermal decomposition of all the Cyclopropanes studied leads to difluorocarbene formation at temperatures in the range 150–220°. The difluorocarbene formed in this way undergoes stereospecific addition to hydrocarbon olefins to give high yields of 1,1-difluorocyclopropanes.