Perfluoroolefins, reaction with

The reaction of oxygen atoms with C4Fe-2 has been examined at room temperature by Johnston and Heicklen.93 Contrary to the reaction with the smaller perfluoroolefins, the important reaction is not cleavage of the double bond. The principal product of the reaction for C4F6-2 pressures between 10 and 100 torr was z-C3F7CFO. Other products were CF3CFO,... 

Systemization of experimental data on the syntheses of heterocyclic compounds with perfluoroalkyl groups from perfluoroolefins is based on reactions with various 1,1-, 1,2-, 1,3-, and 1,4-binucleophilic reagents. While the main features of nucleophilic reactions are preserved, further transformations of the primary products (or adducts, or the products of substitution of the functional groups at the internal multiple bond) occur under the influence of the added functional group containing a heteroatom. Here one can expect dramatic differences in the effect of the nature of the nucleophilic reagent between cyclizations by new nucleophilic centers and centers already available in the molecule. Another important aspect is isomerization of the primary internal olefin into the terminal olefin or internal olefin with a different structure under the action of the nucleophilic agent. This may be critical to the structure of the heterocycle formed. 

Oxidation of internal perfluoroolefins by alkaline solutions of hydrogen peroxide and alkaline and alkaline-earth hypohalides leads to the formation of olefin oxides, the yield of the target product being 40-50%. The reaction with sodium hypochlorite in an alkali in the presence of acetonitrile is an example of epoxidation performed by the nucleophilic attack of the OC1-anion of the multiple bond with further elimination of the chloride anion by the intermediate carbanion (79IZY2509, 79IZV2812, 79RP666176,... 

Since primary alkylamines are binucleophilic reagents, both amino hydrogen atoms are lost in reactions with unsaturated compounds. However, it should be realized that these are rather strong bases catalyzing isomerization of perfluoroolefins. 

Note that for the synthesis of heterocyclic compounds one need not have an a-b-c triad in the substrate it is essential that the triad be formed in the course of the reaction with perfluoroolefins. This is natural since substituted thioureas must exhibit the same properties as thiourea itself. This was verified by reference to the reaction of perfluoro-2-methyl-3-isothiocyanatepent-2-ene with ammonia. When ammonia attacks the carbon atom of the N=C=S group, a derivative of thiourea having an a-b-c triad is formed subsequent intermolecular cyclization can occur via an attack of the S-nucleophilic centers at the multiple bond, forming isomeric compound 56 (03UP1). 

The reactions of some internal perfluoroolefins (perfluorobut-2-ene, perfluoropent-l-ene, and perfluoropent-2-ene) with an S-KF-sulfolane system lead to a five-membered heterocycle-[l,3]-dithiol derivative (82CL201). Thus the reaction with perfluorobut-2-ene gives perfluoro-2-ethyl-2,4,5-tris(trifluoromethyl)-[l,3]dithiol. 

If the N,S- or Y,Y-binucleophile has an a-b-c triad, the character of the heterocyclic product depends on the nature of the nucleophile initiating the reaction with perfluoroolefins and perfluoroazaalkens (Table Y) (03PU1). 

Using pentaerythritol and 1,3-butanediol as nucleophilic agents under conditions of base catalysis in reactions with perfluoroolefins leads to six-membered heterocycles (in particular, to spiro derivatives of 1,3-dioxane) (96ZOB1995). 

Aromatic primary amines are not only binucleophiles at the amino group, but they also exhibit the properties of C,N-binucleophiles. Their reactions with internal perfluoroolefins lead to quinoline derivatives (98JFC(88)169, 94JCS(CC)134, 98T4949). Thus the reaction of aniline with 2//-heptafluorobut-2-ene yields phenyl(2-trifluoromethylquinolin-4-yl) amine (00ZOR109) when the reaction is carried out with the tetrafluoro-ethylene trimer, it leads to 2-trifluoromethyl-3-(l-N-phenylimino-2,2,2-trifluoroethyl)-4-(N-phenylamino)quinoline (98JFC(88)169). 

Perfluoroimines are more reactive than perfluoroolefins because of a fluorine atom connected with the C=N bond. In order to investigate the effects of the electron density and the ring size, a six-membered cyclic perfluoroimine, F-(5,6-dihydro-2//-oxazine) (C-6) and a five-membered cyclic perfluoroimine F-(3,4-dihydro-2/f-pyrrole) (C-5) were subjected to reaction with the fluorinated organosilanes RpSifCHajs (1) [10, 11]. The cyclic perfluoroimines C-6 and C-5 are more sensitive to moisture, and the reactions of C-6 and C-5 with 1 were performed in the presence of spray-dried KF. Similaily to the reaction of flie perfluoroolefin T-2 with 1, aprotic solvents were suitable for the reactions of C-6 and C-5 with 1. The products were handled in anhydrous conditions under an inert atmosphere and/or with a vacuum system. Since the boiling points of trifluoromethylated products and a resulting by-product FSi(CH3)3 were very close to each other, the yields were determined by F NMR or GC analyses of a mixture of a few components, without complete purification. 

Volman173 has found that d>(03) is only 0.03 even with one atm of 02. Consequently, reaction (4-54) is unimportant compared with reaction (4-53). The excited oxygen molecule can also react with perfluoroolefins to ultimately yield oxidation products. The evidence suggests that the initial step is energy transfer83-86... 

Some Rate Constants for Reactions of 02 with Perfluoroolefins Relative to 02 at 25°Ca... 

The reaction of 03 with C2F4, C3F6, and C4F8-2 was studied at room temperature by Heicklen.72 He introduced 03 into the perfluoroolefin in a cell situated in the sample beam of an infrared spectrometer. The products included 02 and CFzO in all cases. With C3Fe and C4Fe-2, CF3CFO was also formed but it was always less important than CFaO. 

II. Reactions of Binucleophilic Reagents with Terminal Perfluoroolefins. 137... 

The second type is the construction of a heterocyclic system from units containing perfluoroalkyl groups or their fragments. Each type has its own advantages and weaknesses. Thus, reactive species used in processes of the first type are perfluoroalkyl radicals and carbocations, and the processes are conducted by elaborate methods (thermolysis, photolysis, electrolysis, one-electron oxidation, etc.), whereas reactions of the second type use condensation of molecules with suitable groups and nucleophilic reactions of perfluoroolefins. 

Another interesting and important technique uses reactions of perfluoroolefins with nucleophilic reagents. The peculiar chemical behavior... 

Terminal perfluoroolefins have two fluorine atoms at the double bond. The carbon atoms of the latter bear a significant positive charge, and the nucleophilic agents easily replace the fluorine atoms at the multiple bond. The reactions of binucleophilic reagents with terminal perfluoroolefins form heterocyclic systems. The first step of the reaction involves a nucleophilic attack at the carbon atom of the double bond, generating a carbanion. The latter is stabilized by elimination of the fluoride ion and formation of a new double bond. Subsequent cyclization by the intramolecular attack of the nucleophilic center at the double bond leads to the formation of a heterocyclic system. For example, when a reaction mixture of hexafluoropropylene and sodium dialkylaminodithiocarbamate in dimethylacetamide is heated with aqueous sodium tetraphenylborate, one obtains the tetraphenylborate salt of 2-dialkylamino-4-trifluoromethyl-4,5-difluoro-l,3-dithiolan-2-yl (78JFC(12)193). This compound is formed by intramolecular cyclization of the S-nucleophilic center. 

The reactions of perfluoroolefins with hexafluoroacetone cyanohydrin under conditions of nucleophilic catalysis yield 3-iminotetrahydrofuran. The latter evidently forms via the intermediate carbanion involved in the intramolecular nucleophilic cyclization (91JFC(54)401). This is an example of synthesis following route f. 

The reactions of terminal perfluoroolefins with oA/zo-bifunctional benzenes used as nucleophilic reagents result in the five-, seven-, and nine-membered benzoheterocycles. In this case, aprotic dipolar solvents are generally employed, and the base is triethylamine. Thus the products of the reactions of oA/zosubstituted anilines with terminal perfluoroolefins are five-membered benzoheterocyclic compounds. 

Intramolecular nucleophilic cyclization is used for the synthesis of four-membered heterocycles. This is a general route for reactions of many perfluoroolefins with primary amines. Thus the interaction between perfhioro-3,4-dimethylhex-3-ene and butylamine in the presence of triethylamine forms N-butyl-perfhioro-2,3,4-trimethyl-2-ethyl-l, 2-dihydro-azete (87ASCC31). In the absence of triethylamine, a mixture of products is obtained, among which are the derivatives of azetidine 15 and azete 16. 

In reactions of primary alkylamines with internal perfluoroolefins, intramolecular nucleophilic cyclization gives a heterocyclic compound with a perfluoroalkyl group. As mentioned above, primary alkylamines can be binucleophilic reagents with nucleophilic centers on the nitrogen atom. Such compounds having an NH2 group form four-membered heterocycles and many polycyclic heterocycles with one nitrogen atom. 

Intramolecular cyclization can afford four-membered heterocycles using reactions of perfluoroolefins with ammonia (81IZV2641). Thus in the reaction of a mixture of isomeric trimers of hexafluoropropylene with ammonia, the fluorine atoms at the double bond are substituted in both isomers. The reaction initially gives a mixture of 2-amino-perfluoro-... 

In this case, a mixture of cis- and ra s-perfluoro-4,5-dihydro-2,3,4,5-tetramethyl-4-ethylfurans is obtained. This is a general reaction, which also works with other perfluoroolefins and alcohols. For example, when the tetrafluoroethylene pentamer reacts with allyl alcohol in the presence of bases, the initial reaction is nucleophilic addition at the multiple bond, forming olefin 44, followed by the formation of perfluoro-4-ethyl-2,3,4,5-tetramethyl-4,5-dihydrofuran 45 in the presence of KF (87ASCC31). 

The formation of the perfluoroalkyl derivatives of 1,3-dioxolane in reactions of perfluoroolefins with ethyleneglycol is a general process. It was... 

This methodology yields various heterocyclic compounds in reactions using internal perfluoroolefins or systems with conjugated multiple bonds as precursors. Hopefully, this approach will find wide use and new information will permit more profound generalizations. On thermolysis or photolysis aziridines are converted into azomethine ylides, reacting with perfluoro olefins (for example, hexafluoropropylene and perfluorobut-2-ene) to give pyrrole derivatives (autoclave, 160 °C) (76CJC218). 

Reactions of perfluoroolefins with aliphatic aldehyde oximes lead to cyclization product 87 without a rearrangement of the carbon skeleton. 

These examples demonstrate the utility of bifunctional nucleophiles in reactions of perfluoroolefins with an internal multiple bond leading to various heterocyclic compounds with perfluoroalkyl substituents. 

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