Fluorine-aryl substitution

Nucleophilic fluorine-aryl substitution in iodine pentafluoride with tetrakis(pentafluoro-phcnyl)silane or tris(pentafluorophenyl)bismuthane produces high-purity (pentafluorophen-yl)iodine tetrafluoride in good yield.133,134... 

The formal addition of perfluorinated pyridine, pyrimidine, pyridazine or of pentafluorobenzo-nitrile to fluorinated acetylenes in the presence of cesium fluoride in sulfolane leads to fluorinated aryl-substituted alkenes. " In the first reaction step fluoride ion adds to the fluorinated acetylene to give a vinyl carbanion, which substitutes, in a second step, a fluoride ion from the perfluorinated aromatic compound. Some examples of this type of reaction are shown by the formation of... 

Figure 11.12 Structure of o-fluorinated aryl substituted NHC complexes 56 and 57.

As noted, these zinc reagents find extensive application in the preparation of fluorinated styrenes [113, 114], aryl-substituted fluorinated propenes [114],fluor-inateddienes [115,116], and tnfluorovinyl ketones [117], as illustrated in equations 83-88... 

The fluorines of various aryl chlorine, bromine, and iodine difluorides and tetrafluorides appear in their fluorine NMR spectra as singlets (unless there is a fluorine or trifluoromethyl group in the ortho position), which are sensitive to both the aryl substitution and the solvent (Scheme 7.35). The variations in chemical shifts, all given as reported, are distinctive. 

Several fluorinated aryl ethers 134 were prepared from the reaction of the 11,12/3-oxirane 133 <1994TL2129> with substituted benzyl alcohols (Equation 13 Table 8) <1995JME4120>. 

Thus, aryl-substituted antimony fluorides provide replacement of chlorine by fluorine atoms in aromatic compounds containing trichloromethyl and pentachloro- or dichlorotri-fluoroethyl groups. Their activity as fluorinating agents decreases in the order tetrafluoro(phenyl)-A5-stibane > trifluorodi(phenyl)-25-stibane >antimony(lIl) fluoride dill uorotri(phenyl)-/i.5-stibane. 

Fluorinated triazolines (Scheme 29) are particularly stable and require high temperatures for thermolysis when aziridines are obtained.145 Thermolysis of aryl-substituted triazolines is not well investigated144,175 the l-p-nitrophenyl-5-phenyl compound yields exclusively aziridine, whereas the 1,4-isomer gives the imine as the major product.175 1-Heterocyclic-substituted 5-vinyltri-azolines (Scheme 31) give S-vinylaziridines, which undergo thermal isomerization to azepine derivatives (e.g., 89).183... 

The majority of the more important methods for the preparation of fluorinated compounds by substitution reactions have been reviewed in the previous sections. There are, however, some additional important synthetic procedures which should also be mentioned, mainly those concerned with the introduction of fluorine by substitution of functional groups containing boron, silicon and tin the reactions of organotin compounds are the most well-studied to date. These reactions are excellent synthetic methods for obtaining vinyl and aryl fluorides (sec also Section 1.1.1.1.). 

Ruzziconi and coworkers used the ceric ammonium nitrate promoted C—C forming reaction to prepare polycyclic homo- and heteroaromatics starting from aryl-substituted silyl enolates and, more recently, the same strategy has been applied to the preparation of fluorinated naphthaldehydes and naphthyl ketones . 

Zajc, BZupan, M. Fluorination with xenon difluoride. 37. Room-temperature rearrangement of aryl-substituted ketones to difluoro-substituted ethers. J. Org. Chem. 1990,55(3), 1099-1102. 

---