Perfluoro-2-butyne, reaction

Perfluoro-2-butyne is, as expected, even more reactive in its reaction with phenyl azide [75]. Its reaction with 7V-phenylsydnone is also reported [79] (equation 13). 

The reaction of a germacyclohexadiene, 13, with perfluoro-2-butyne, 14, followed by thermolysis of the obtained product, yields a digermacyclobutane51 (Scheme 11). 

Attempts to isolate the silole monomer 2 or to trap it by reaction with maleic anhydride or perfluoro-2-butyne have failed. This is surprising given the successful trapping of 1-methylsilole5 and 1,1-dimethylsilole10. The authors conclude that silole 2 is not very reactive in Diels-Alder cycloadditions, except toward self-reaction19. 

Pyridinium (trifluoroacetyl)methylide forms [3-1-2] cycloadducts with a wide variety of perfluorinated and partially fluorinated olefins, alkynes, and nitriles [86JFC(34)275]. Photolysis of a mixture of hexafluoro-3-diazobutan-2-one and perfluoro-2-butyne in the gas phase results in the formation of tetrakis(trifluoromethyl)furan a ketocarbene is the key intermediate of this reaction sequence (87JOC2680) (Scheme 79). 

This concept can also be applied for the synthesis of 3-perfluoroalkyl-and 3,4-bis(perfluoroalkyl)-substituted pyrroles [82JOC4779 91JFC(53)-285]. The Diels-Alder adduct from A-(tert-butoxycarbonyl)pyrrole and perfluoro-2-butyne exhibits remarkable thermal stability, but after a second [4 + 2] addition of 2,4,6-trimethylbenzonitrile oxide the newly formed adduct is capable of a retro-Diels-Alder reaction, giving 3,4-bis(trifluoro-methyDpyrroles (82S313). 

Few examples of cycloaddition reactions of the type [2 + 2+1] where fluorosubstituted compounds are participating are known. Perfluoro-2-butyne and elemental sulfur react to give tetrakis(trifluoromethyl)thio-phene [84JFC(25)47]. Analogously, a mixture of tetrakis(trifluoromethyl-thio)thiophene, 2,3,4-tris(trifluoromethylthio)-5-trifluoromethylthiophene, and tetrakis(trifluoromethylthio)-l,2-dithiin was obtained from bis(triflu-oromethylthio)acetylene and sulfur at 170°C (85JHC1631) (Scheme 91). 

Formation of the lithium derivative of trifluoropropyne was described in the preceding section [294] and the various acetylides, RfC=CM, had been prepared previously (e.g. M = Cu, Ag, Hg Rp = CF3,C2F5,CF3CH2) [289]. However, most studies concerning the reactions of perfluoroalkynes [291] have centred on the use of perfluoro-2-butyne, as this is commercially available. 

Cycloadditions [40] Perfluoro-2-butyne is a highly reactive dienophUe and many [4 + 2] cycloaddition and 1,3-dipolar addition reactions involving this alkyne have been reported (Table 7.20). Moreover, [2 + 2] additions with hydrocarbon alkenes are possible (Table 7.20). 

Table 7.20 Cycloaddition reactions with perfluoro-2-butyne...

Heptafluoro-2-butene, which is readily available in a laboratory synthesis from hexa-chlorobutadiene, may be used as a synthon for perfluoro-2-butyne in cycloaddition reactions where in situ elimination occurs [322] (Figure 7.92). 

Free-radical additions Free-radical addition reactions involving perfluoro-2-butyne are also possible, as indicated in Figure 7.95 [327, 328]. 

Tl6-CH3C6H5)2Zr[P(CH3)3] reaction with (Me3Sn)2 10.3.2.2.2 CnH25CJp2Pt PtCI(CH3)[P CH3)2(C6H5)]2 insertion reaction with perfluoro-2-butyne 11.3.3.2... 

Cakhim.— Perfluorobut-2-yne is released in low yield when the glass-like matrix obtained by co-deposition of calcium vapour and perfluorobut-2-ene on a cold (-196 °Q surface, in vacuo, is allowed to warm up. Under similar circumstances, perfluoropropane does not react perfluoro-propene and -cyclobutene give only large amounts of polymer . The butene - butyne defluorination is believed to involve the intermediate CF,-CF C(CF,)-CaF. (See p. 427 for information on atomic Ca-C F reactions.)... 

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