Hexafluoro-2-butyne cycloadditions

All pnictohetarenes with Y = P, As, Sb, and Bi react with dienophiles such as hexafluoro-2-butyne affording hetero-barrelene derivatives (P- at 100 °C, As- at 25 °C, Sb- and Bi-pnictohetarenes at even lower temperatures). The equilibrium low-temperature dimerizations of bismabenzene and stibabenzene (37-38) also involve such cycloadditions. 

The highly exothermic cesium fluoride catalyzed isomerization of hexafluorobutadiene (9) via 10 to hexafluoro-2-butyne (11) is another example [5] that shows that the fluorine atom is preferably bonded to the carbon atom through the sp3-hybridized orbital rather than through the sp2 orbital [6]. And here again, Bent s rule plays an important role in the isomerization [7]. The thermal reaction of hexafluoro-1,3-butadiene provides perfluorotricyclo[3.2.0.02,6]octane (15) as a stable final product via sequential intra-and/or intermolecular cycloaddition at 200°C [8]. In contrast, the parent hydrocarbon (16)... 

The twisted alkene present in acetoxydithiocin (176 R = Ac) was suggested to be a possible cause of its relative unreactivity as a diene in Diels-Alder cycloaddition reactions. No reaction is seen with maleic anhydride, tetracyanoethylene, or hexafluoro-2-butyne at 45 °C higher temperatures were precluded by the thermal instability of (176 R = Ac) <78T363i>. iV-Phenyltriazolinedione reacted with (176 R = Ac), but afforded no identifiable products. 

Another type of cycloaddition used to produce, in this case, 3,4-bis(trifluoromethyl)thiophene 170 was the reaction of hexafluoro-2-butyne with mesoionic thiazolium system 168. Phenyl isocyanate was eliminated from the initial adduct, giving the substituted thiophene in more than 90 % yield [89]. 

The most conunon synthetic procedure for the preparation of perfluoroalkylated 1,2,3-triazole derivatives is 1,3-dipolar cycloaddition of azides to diverse unsaturated dipolarophiles containing perfluoroalkyl substituents. Thus, in 1966 Carpenter et al. carried out the cycloaddition of benzyl azide to perfluoroalkyl substituted acetylene derivatives leading to the formation of trifluoro-methyl-l,2,3-triazolines and 1,2,3-triazoles [39]. In this paper a synthesis of l-benzyl-4,5-bistrifluoromethyl-l,2,3-triazole 31 from hexafluoro-2-butyne was described. 

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