Cyclopropanes polyfluorinated

Fluorinated carbocations play an important role as intermediates in electrophilic reactions of fluoroolefins and other unsaturated compounds. For example, F-allyl cation 1 was proposed as a reactive intermediate in reactions of HFP with fluoroolefins catalyzed by Lewis acids [7]. The difference in stability of the corresponding allylic cations was suggested as the explanation for regio-specific electrophilic conjugated addition to CF2=CC1CF=CF2 [11]. Allylic polyfluorinated carbocations were proposed as intermediates in the reactions of terminal allenes with HF [53] and BF3 [54], ring-opening reactions of cyclopropanes [55], Carbocations are also an important part of the classic mechanism of electrophilic addition to olefins (see Eq. 2). This section deals with the questions of existence and stability of poly- and perfluorinated carbocations. 

Unfortunately, structures of monosubstituted cyclic hydrocarbons which would allow a systematic correlation between C—F bond distances and ring size have not been reported in the literature. Some polyfluorinated and the perfluorinated cyclopropanes were studied by MW and ED and the C—F bond lengths are listed in Table 14. If only one fluorine is bonded to a ring carbon atom, the C—F bonds are long ca 137 to 139 pm), very similar to that in fluoromethane [139.1(1) pm]. An unexpected result is that the cis standing bonds... 

Under SbCls catalysis oxygen-bromine exchange between benzaldehyde and o-chlorobenzal bromide proceeds at 100 °C to give benzal bromide and o-chlorobenzaldehyde in moderate yields [88]. Isomeric transformation of perfluorinated epoxides to the corresponding carbonyl compounds occurs in the presence of SbFs [89]. Isomerization of polyfluorinated olefins, cyclohexadienes, and cyclopropanes is also promoted by the action of SbFs [90]. 

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). 

Polyfluorinated BOX ligand 228 provides a useful copper complex catalyst, which can be recovered easily from the reaction mixture by a fluorous solvent system [159]. Benaglia and coworkers reported that an F-BOX ligand with CuOTf catalyzed the asymmetric cyclopropanation of diazoacetate in a CgFig/CHaCN biphasic mixture the F-BOX ligand was readily separated from products by phase separation and recovered from the reaction mixture (Scheme 1.105). 

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See also in sourсe #XX -- [ , ]

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