Trifluorovinyl Groups

A more efficient agent than peroxy compounds for the epoxidation of fluoro-olefins with nonfluonnated double bond is the hypofluorous acid-acetomtrile complex [22] Perfluoroalkylethenes react with this agent at room temperature within 2-3 h with moderate yields (equation 13), whereas olefins with strongly electron-deficient double bond or electron-poor, sterically hindered olefins, for example l,2-bis(perfluorobutyl)ethene and perfluoro-(l-alkylethyl)ethenes, are practically inert [22] Epoxidation of a mixture of 3 perfluoroalkyl-1-propenes at 0 C IS finished after 10 mm in 80% yield [22] The trifluorovinyl group in partially fluorinated dienes is not affected by this agent [22] (equation 13)... 

Trifluorovinyl Groups. Trifluorovinyl groups have characteristic chemical shifts and coupling constants that are exemplified in Scheme 3.49 (see Chapter 6 for more details and examples). 

The fluorine substituent at the 2-position of a trifluorovinyl group is much more highly shielded than the other two fluorines, and its presence gives rise to an enhanced split of the diastereotopic fluorines at the 1-position and enhanced coupling constants, both geminal and vicinal. 

A typical 19F NMR spectrum of a compound with a trifluorovinyl group is given in Fig. 6.20. This compound is the chemical precursor of the drug known as EF5, which is used in positron emission tomography imaging to detect hypoxic tissue. 

Dolbier and coworkers have utilized similar coupling with 1,2-diiodonaphthalene and 9-iodo-10-nitrophenanthrene to introduce two trifluorovinyl groups onto the aromatic... 

For a long time it was believed that the trifluorovinyl group is not basic enough to stabilize an a-carbocationic center, and perfluorinated allylic cations were thought not to be stable [15,21,59]. However, in 1984 the formation of the F-methallyl cation 30 in the reaction of PFIB with SbF5 in S02C1F solvent was reported [74], followed by the F-allyl cation (1) [75] ... 

Not surprisingly, trifluorovinyl groups are cleaved by aqueous potassium hydroxide from, for example, (CF2=CF)4Si, Et2Si(CF=CF2)2 and Et3SiCE=CE2, which may be obtained by the Grignard or lithium routes [100-104] (Figure 10.47). 

Thermal dimerization of perfluoroalkcnes is also a good approach for obtaining interesting dimeric fluoro-substituted compounds. A -[4-Phenoxy-3-(trifluorovinyl)phenyl]phthalimide (3), which is a model for polyimides containing trifluorovinyl groups, undergoes thermal dimerization at 140-160"C to give predominantly the trtf .s-1,2,3,3,4,4-hexafluoro-l,2-bis(2-phenoxy-5-phthalimidophenyl)cyclobutane (4).6 See Section 2.1.1.6.2. for a more detailed discussion of this [2 + 2]-cycloaddition process. 

These are consistent with a lack of interaction between the 7r-electrons of the trifluorovinyl group and the boron p,-orbital. 

By attaching trifluorovinyl groups to the traditional HTMs, a series PFCB-based cross-linkable HTMs were developed (Figure 8.6). It is well-documented that trifluorovinyl aromatic ether can undergo thermal... 

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