From difluorocarbene

Mitsch and Neuvar have shown that perfluorovinyl cyclopropane isomerises at 131-183 °C to perfluorocyclopentene by a clean unimolecular reaction. The activation energy is about 15 kcal.mole less than for the reaction involving the parent hydrocarbon - . Perfluoroallylcyclopropane decomposes unimolecu-larly at 196-250 °C to perfluoro-l,4-pentadiene and perfluorocyclopropane plus perfluoroethylene (the latter two products presumably from difluorocarbene formed in the initial reaction). Arrhenius parameters are. <4 = 6.3 x 10 sec , E = 42.7 kcal.mole . Placzek et 499,500 reported on the rates of... 

Neuvar and Mitsch" examined the thermal decomposition of difluorodiazirine in a static system at 123-170 °C. Products formed were nitrogen and perfluoro-ethylene plus perfluorocyclopropane, the latter two compounds being presumably formed from difluorocarbene initially produced, viz. 

The factors determining which of the two product types 10 or 11 results are not fully understood. It seems clear that a nonconcerted mechanism is operating in the case of dichloro- and di-bromocarbene adducts, and in the formation of a-difluoro ketones from difluorocarbene adducts. 

However, the formation of a-fluoro-a,j8-unsaturated carbonyl compounds from difluorocarbene adducts may proceed in some cases via a classical cationic disrotatory cyclopropyl to allyl rearrangement, e.g. 12- 13->14. °... 

Dialkylcadmium reagents are often useful alternatives to the more reactive Gngnard reagents in the preparation of ketones from acyl halides However, bis(trifluotomethyl)cadmium glyme is decomposed by acyl halides and does not give trifluoromethyl ketones [, 124] Nevertheless, this reaction can be used as a low-temperature source of difluorocarbene [S, 124] (equation 102)... 

Phase-transfer systems for generating fluorohalocarbenes from the corre spending haloforms are simple and effective with nucleophilic olefins [5J, 54 55, 56, 57, 58, 59] (Table 3 and equations 23 and 24), and the process was extended recently to difluorocarbene [60] Chlorofluorocarbene also can be generated from fluorotrichloromethane and utanium(O) produced in situ (T1CI4 + L1AIH4) Yields of gem-chlorofluorocyclopropanes range from excellent (85% for a. meth ylstyrene) to poor (12% for 1-hexene) [61]... 

UV irradiation (A>300nm) of an argon matrix containing tetra-fluoromethane led to the formation of difluorocarbene CF2 (Milligan and Jacox, 1968a). It was shown that the IR spectrum of this species contains three bands at 1222 (i i), 1102 (v ), and 668 (i 2)cm . Some time later difluorocarbene was stabilized in a neon matrix at 4.2 K from the gas phase after vacuum flash pyrolysis (1300°C) of perfluoroethene (Snelson, 1970b). In this case the IR bands of CF2 differed from those in an argon matrix by less than 2 cm . ... 

It is well known that azomethine ylides, which are usually formed in situ, are very good substrates for 1,3-dipolar cycloadditions. The group of Novikov and Khlebnikov [328] generated such a 1,3-dipol by reaction of difluorocarbene formed from CBr2F2 (2-626) with the imine 2-627. Cycloaddition of the obtained 2-629 with an ac-... 

The metathesis reaction of fluorinated alkyl iodides with reagents such as CdMe2 is a well-established procedure for the synthesis of fluoroalkyl cadmium derivatives. A recent application of this method has allowed for the synthesis of compound 186, as shown in Scheme 22.248 This reaction is accompanied by formation of 187, which results from the insertion of the difluorocarbene in the methyl-cadmium bond. Presumably, the difluorocarbene is generated by a radicalar process involving HCF2I and CdMe2. 

Finally, the addition of difluorocarbene (generated from FjClCCOjNa) to steroidal acetylenes has been achieved24-26 giving rise to exotic cyclopropenones bearing steroid systems as substituents, e.g. 19/20. 

CVD processes can also be used to grow polymers from nanocarbons. An important example is the coating of a CNT forest with a thin layer of poly(tetrafluorethlylene) (PTFE) via hot filament CVD to produce a superhydrophobic substrate [245]. Here, a vertically aligned MWCNT forest was prepared and placed in a CVD reaction chamber. Hexafluorpropylene oxide gas was then thermally decomposed to form the reactive radical difluorocarbene (CF2) and flowed over the CNT substrate along with a small amount of initiator where direct polymerization of PTFE onto the CNTs occurred [245]. 

The facile quantitative addition of mercaptoethanol 200 d onto the double bonds of bicyclopropylidene derivatives has successfully been applied to separate the difluorocarbene adduct 122 from the starting material 121 (see Scheme 24) [116]. 

Dipolar cycloaddition is another route to benzopyrrolo[l,2-a]azepines by pyrrole ring formation. The azomethine ylide derived from imine 88 and difluorocarbene adds to DMAD to produce dimethyl 3-fluoro-9H-dibenzo[c,/]-pyrrolo[l,2-fl]azepine-l,2-dicarboxylate 89 in 20% yield (Equation (12)... 

Difluorocarbene, generated from fluorosulfonyldifluoroacetate, adds on double bonds and aromatic or vinylic ketones, affording fluorinated cyclopropanic ethers. ... 

S -Mono-, di-, and trifluoro derivatives of methionine and 5-fluoroalkyl derivatives of cysteine are accessible through fluorination. Thus, fluorination of methionine sulfoxide with xenon fluoride, or more easily using DAST, provided 5-monofluor-omethionine. Photochemical trifluoromethylation of homocysteine leads to 5-trifluoromethionine. These S -fluoroalkyl compounds are also available through fluoroalkylation of homocysteine. Thus, the addition of difluorocarbene (formed from Freon 11 (CHF2CI)) affords S -difluoromethionine. ... 

Trifluoromethylzinc reagent can be prepared from the direct reaction of dihalodifluoromethane and zinc in DMF [42] (Scheme 13). In this remarkable reaction, DMF functions both as a solvent and reactant, and difluorocarbene is the reactive intermediate, based on mechanistic experiments. Dolbier et al. have utilized this reaction as a difluoromethylene cyclopropanation reaction [43] (Scheme 14). 

The reaction proceeds via difluorocarbene elimination from the CF3C group and insertion of the formed CF2 into a C — F bond. 

Difluoro(methylene)cyclopropanes have been obtained in modest yields from allene by difluorocarbene addition.61 The difluorocyclopropane moiety proved stable upon... 

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