Thermolysis, of perfluoroalkyl

Perfluoroalkylation of substituted benzenes and heterocyclic substrates has been accomplished through thermolysis of perfluoroalkyl iodides in the presence of the appropriate aromatic compound Isomeric mixtures are often obtained W-Methylpyrrole [143] and furan [148] yield only the a-substituted products (equation 128) Imidazoles are perfluoroalkylated under LTV irradiation [149] (equation 129). 4-Perfluoroalkylimidazoles are obtained regioselectively by SET reactions of an imidazole anion with fluoroalkyl iodides or bromides under mild conditions [150] (equation 130) (for the SET mechanism, see equation 57)... 

Thermolysis of perfluoroalkyl(N-pentafluorosulfanyl)azidoazomethines 28 afford N-perfluoroalkyl-N -pentafluorosulfanylcarbodiimides 29 (R = CF3, C2F5, NFaCFs). ... 

The thermolysis of perfluoroalkyl(N-pentafluorosulfanyl)azidomethines 18 affords N-fluoroalkyl-N -sulfanylcarbodiimides 19 (Rf=CF3, C2F5). ... 

All the S-, Se-, and Te-(perfluoroalkyl)dibenzothiophenium, -selenophenium, and -tellurophenium salts synthesized above are stable crystalline materials at room temperature. Their melting or decomposition points (dec. p) are higher than 100°C. Nitro substituents decrease their stability [S-salt 17 mp 155°C > dinitro S-salt 39 dec. p 130-135°C]. The chalcogen stability increases in the order S < Se < Te [dec. p S-salt 39 130-135°C < Se-salt 40 198-200°C < Te-salt 41 275-280°C]. Thermolysis of S-salt 17 at 200 C gave trifluoromethyl triflate (50) and dibenzothiophene (51) in high yields (Eq. 12). Thermolysis of dinitro S-salt 39 at 140°C gave 50 and dinitrodiben-zothiophene 52 (Eq. 13). 

N-nitroso-N-trifluoromethyl trifluoromethanesulfonamide [78], photolysis of bis-(trifluoromethyl)tellurium [79], thermal AIBN-induced decomposition of bis-(trifluoromethyl)mercury [80], thermolysis of highly branched perfluoro-carbons [81], and even thermolysis of persistent perfluoroalkyl radicals such as that discovered by Scherer [39, 45]. Recently it has even been found that per-fluorocarbons can be a source of perfluoroalkyl radicals when they undergo photoinduced reduction by NH3 or by Cp2TiF2 [82,83]. 

Thermal or photolytic cleavage of the O—Cl bond in a perfluoroalkyl hypochlorite is readily effected, but in general members of this class are much more stable thermally than their hydrocarbon analogues. Trifluoromethyl hypochlorite is the most stable of the series (thermolysis occurs only slowly at 150°C ), rupture of the O—Cl bond becoming easier as the perfluoroalkyl chain lengthens or branches > decomposition occurs in a manner apparently analogous to that of perfluoroalkyl hypofluorites, e.g. 

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. 

A number of thermal and photochemical transformations of the 1,2-diazine system are noteworthy. Thermolysis isomerizes pyridazines into pyrimidines and/or pyrazines, as has been demonstrated for a series of perfluoro and perfluoroalkyl derivatives (see p 288). Pyridazine is converted into pyrimidine at 300°C. A process of valence isomerism is thought to be responsible for the thermal isomerization of pyridazines via diazabenzvalenes (simplified as 3 and 4). 

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