2- Butyne perfluoro

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. 

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Perfluoro-2-butyne reacts with sulfur in carbon disulfide to give l,2-bis(tn-fluoromethyl)vinylene trithiocarbonateA and a subsequent products [2] (equation 4). 

Cesium fluoride-promoted telomenzation of equimolar amounts of perfluoro 2-butyne and 2-bromoperfluoro-2-butene gives a mixture of hexadienes or, with... 

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). 

In another study the kinetics and mechanism of an unprecedented T/2-vinyl isomerization of a highly fluorinated tungsten(II) metalla-cyclopropene complex was studied (92). Photolysis of a tungsten(II) tetrafluoroaryl metallacycle 1 and perfluoro-2-butyne results in the formation of the kinetic rf -vinyl complex 2 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. Upon heating 2 is converted to the thermodynamic rf -vinyl complex 3 in which the fluoride ligand is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand as shown in Scheme 1. 

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. 

Fluoroalkenes and fluoroalkynes, e.g. perfluoropropene, perfluoro-2-butyne and perflu-orocyclobutene, insert into M—Sn bonds, M = Mn, Fe (equation 145)341b. 

The [3 -I- 2] cycloadducts from pyridinium methylides and perfluoro-2-butyne as well as 3,3,3-trifluoropropyne in the presence of sodium hydride are spontaneously transformed into the trifluoromethyl-substituted indoli-zines [91 JFC(51)407] (Scheme 72). 

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 polymers and oligomers When perfluoro-2-butyne is heated, either alone or with halogen compounds or a metal carbonyl, hexakis(trifluoromethyl)benzene is obtained [303-306] (Figure 7.86). This is a very interesting compound that gives stable valence isomers on irradiation with ultraviolet light (see Chapter 9, Section HE,... 

A high-molecular-weight, insoluble polymer is obtained when perfluoro-2-butyne is subjected to various initiators for free-radical polymerisation (Figure 7.87). The off-white colour of this material is remarkable for a polyacetylene [307, 308]. Indeed, it is largely ignored in discussions on polyacetylenes because, of course, the fact that it is not coloured also means that the system is not conjugated the trifluoromethyl groups keep the TT-systems out of plane relative to each other. 

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]. 

Other systems Additions of perfluoro-2-butyne [143] and acetylene dicarboxylic ester [139] to perfluoro-aromatics will also occur (see Table 9.9 and Chapter 7, Section lllB). The extending anion may be trapped, and the more reactive the aromatic compound used, the more effective the competition with polymer formation (Figure 9.57) [144]. 

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... 

FIGURE 4.3 TEM image of pure carbon made from perfluoro-2-butyne and Li-amalgam at 25°C. The LiF byproduct was extracted from the raw material by water. 

Two other approaches to the furan derivative 67 have been described (a) from perfluoro-2-butyne and involving the novel cyclopropenyl ketone derivative 74154 and (b) by ozonolysis of hexakistrifluoromethylbenzvalene (75), followed by treatment of the ozonide (76) with triphenylphosphine and... 

Both isomers were characterized by their adducts with perfluoro-2-butyne (PFB) and 2,5-diphenylisobenzofuran (DPIBF), respectively. At 0°C, MBD dimerizes in a 4 + 2 cycloaddition to give an adduct, D which reverts to MBD at 80°C which then gives a 2 + 2 dimer, D2, whose structure is as determined by X-ray analysis. 

When heated with perfluoro-2-butyne at 175 for 12 hours, 2-pyridone gives... 

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