Fluorination Approaches

The oligomers and polymers described above retain a number of protons that may be undesirable for some demanding applications. The obvious solution is to replace hydrogen with fluorine, and it appears that the only prospect for such transformation is radical fluorination. By the fluorination approach, these F-vinyl ether homopolymers, owing to their unique structures, may provide a new route to novel perfluoropolyethers. 

Adopting the fluorination approach in polyimides, relative permittivities can be reduced from 3.4 to 2.8, a common structure incorporating the hexafluoroLsopropylydene moiety (6F) ... 

Cyclic imines can be also prepared using traditional chlorination-fluorination approach. Ulrich et al. prepared imines 81 in a good yield by reacting imides 47 with PCI5, followed by the treatment of chlorinated products with AgF. ... 

This chapter deals with recent advances in the application of electrochemical electron transfer reactions to the synthesis of fluorinated organic substances. The effect of fluorine atoms on the reduction and oxidation potentials of organic compounds is discussed first. Subsequently, recent applications of the electrochemistry to the conversion and functionalization of fluoro-organics (building-block approach) are described. Finally, methods for selective electrochemical fluorination of organic molecules (direct fluorination approach) are briefly considered. 

A nucleophilic fluorination approach towards fluoroindoles was also elaborated. Using nucleophilic substitution of phenyliodonium group by fluoride under heating, 2-fluoroindole 25 and 3-fluoroindole 5 were prepared in good yields. The intermediate phenyl(indolyl)iodonium salts 26 and 28 were easily synthesized by treatment of (2-indolyl)trialkylstannane 24 [11] or indole 27a [12] with the corresponding polyvalent iodine compounds. 

Li and co-workers have developed a silver catalysed decarbo>ylative fluorination approach, which proceeds under aqueous conditions using Selectfluor (Scheme 15.24). A range of Ag sources can be effectively... 

Scheme 15.38 Fluorination approaches to a precursor of 6a-fluoroursodeoxycholic acid.

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