Terminal perfluoroolefins

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

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 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. 

Subsequent intramolecular nucleophilic attack by the second O- or N-nucleophilic center affecting the carbon atom of this multiple bond leads to a cyclization product. This demonstrates the role of the intermediate (and rather reactive) terminal perfluoroolefin, directing the subsequent O- and N-nucleophilic attack. 

With perfluoroolefins atomic oxygen does not give normal adducts, but instead causes cleavage of the double bond.11 With terminal olefins triplet difluoromethylene apparently is a major product, and its addition to excess olefin to form perfiuorocyclopropanes is quenched by molecular oxygen. 

Synthetic methods have limited the preparation of saturated perfluoropolyethers. The most successful perfluoropolyether synthetic chemistry has been DuPont s anionic polymerization of perfluoroepoxides, particularly hexafluoro-propylene oxide and tetrafluoroethylene oxide (39). Their synthetic procedure is a three-step scheme for saturated perfluoropolyether production involving oxidation of perfluoroolefins to perfluoroepoxides, anionic polymerization to acyl fluoride terminated perfluoropolyethers, and conversion of acyl fluoride end groups to unreactive end groups by decarboxylation reactions or chaincoupling photolytic decarboxylate reactions. 

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. 

Epoxidation of terminal and internal perfluoroolefins by aqueous solutions of alkaline and alkaline-earth hypohalides in alkaline media is conducted in the presence of aprotic solvents (79IZY2509, 79RP666176). 

The interaction of perfluoro-2-methylpent-2-ene and epichlorohydrin in the presence of CsF or triethylamine in aprotic solvents forms tetrahydrofuran 49. The reaction occurs by cleavage of the epoxide ring under the action of the fluoride ion generating an O-nucleophilic center, which reacts at the multiple bond of the perfluoroolefin. Further cyclization the new terminal double bond gives the final reaction product. 

The yields of perfluoroolefin and the decomposition temperature depend on the cation of the salt. The sodium salt of normal-chain perfluoroalkanoic acids gives the terminally unsaturated perfluoroolefin in yields ranging from 65% to... 

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