Difluoromethylene, trapped

The photolysis and pyrolysis of difluorodiazirine has been shown to involve difluoromethylene and stereospecific addition to 2-butene indicates that it is probably in a singlet state. In argon or nitrogen matrices, Cp2 has been detected by spectroscopic measurements . Products arising from the thermolysis or photolysis of fluoromethoxydiazirine, cyanofluorodiazirine, difluoroaminodiazirine and chlorofluorodiazirine have been reported the main feature of these reactions is that the intermediate carbene in all cases can be trapped by olefin reagents, whereas fluorocarbenes from other sources are quite unreactive. 

Nucleophiles therefore attack exclusively at the gem-difluoromethylene carbon of diflu-oroalkenes to form (3-fluorocarbanions (1). The chemical fates of 1 are mostly dependent on the structures of the alkenes and the reaction conditions. The typical reaction pathways of 1 are classified into three as shown in Scheme 2.17. In aprotic solvents, the carbanions (1) undergo defluorination, affording a-substituted monofluoroalkenes (2). Meanwhile, in pro tic solvents or in the presence of electrophiles in aprotic solvents, the carbanions (1) can be trapped with a proton or an electrophile to give addition products (3). The third case is S -type addition where substrates must have a leaving group on the y -carbon of 1 such as an alkoxy or an acyloxy group. 

Difluoromethylene(trifluoromethyl)phosphane (216), available most conveniently by thermolysis of the stannylphosphane (215), dimerizes and trimerizes on warming from a cold trap to give the... 

Perfluoropropene oxide is a convenient, volatile, thermal source of difluoro-carbene, and its use in the preparation of fluorocyclopropanes has been further exemplified, perfluorinated, polyfluorinated, and hydrocarbon olefins being employed as substrates (see also p. 17) it has also been employed to convert perfluorobut-2-yne into 3,3-difluoro-l,2-bis(trifluoromethyl)cyclo-propene. Qose examination of the reaction between the epoxide and a mixture of cis- and rra .r-l-chloro-l,2-difluoroethylene at ca. 200°C has revealed that stereospecific addition of difluorocarbene takes place, but that loss of configuration can subsequently result from slow thermal isomerization of the cyclopropane product. Thermal decomposition of perfluoropropene oxide at 200 "C in the absence of a trap yields mainly perfiuorocyclo-propane and trifluoroacetyl fluoride together with tetrafluoroethylene, perfluoroisobutene oxide, perfluorobut-l-ene, and poly(difluoromethylene). 

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