Ortho fluorines

For the ortho-fluorinated compounds, dioxygenation may occur with simultaneous decarboxylation and loss of fluoride. 

Cooper, M. A. NMR Spectra of Some Iodo- and Bromofluorobenzenes. Novel Solvent Effect on Ortho Fluorine-Fluorine Couplings. Org. Mag. Res. 1969, 363. 

Regarding other fluorine positions on the phenyl ring it is observed that ortho-fLuorine atoms give the largest and most sensitive values some reported values<1966,19) are shown in Table XXIII. For the purposes of comparison the data of Nichols<1969,121) shown in Table XXIV is of interest. 

Some typical values of ortho-fluorine coupling constants... 

In general, substitution of the activated fluorine by sulfur nucleophiles proceeds smoothly under gentle conditions (Table 1). As fluorine in the ortho position to a nitro group is more activated than one in the para position, in the case of difluoronitrobenzenes a selective elimination of the ortho fluorine is possible by keeping the molar ratio of RS /RF low. The activated fluorine can be successfully replaced not only by alkane- or arenethiols, but also by the sulfide ion. giving access to substituted benzcnethiols, and by benzenesulfinate,14 giving access to... 

Intramolecular cyclization in perfluoroaromatic systems proves useful for the synthesis of heterocyclic compounds [72] For example, the Fischer indole synthesis, which normally requires the presence of an ortho proton, occurs satisfactorily with an ortho fluorine in theperfluoronaphthalene senes [73] (equation 37)... 

The effectiveness of these anions depends to a large degree on the integrity of the jl-X linkage. The p,-NH2 compound is air and moisture stable and exhibits a particularly strong bridge, possibly by virtue of four N-H- F hydrogen bonds between ortho fluorine atoms and the amido NH protons. Activation of common metallocenes with the trityl salt... 

Very dilute fluorine was reacted with aromatic hydrazones to produce a benzylic CF2 moiety (equation 174)294. Aromatic fluorination with elemental fluorine had also been attempted. Purrington and Woodard found that ortho fluorination usually took place with systems carrying either electron-donating or electron-withdrawing substituent, although neither the yields nor the conversions were very high. They studied the influence of strong... 

Interestingly, the H-5 chemical shift of 4-(2-fluorophenyl)-l,2,3-selenadiazole (102) appears as a doublet (J = 0.9 Hz), arising from coupling with the ortho fluorine atom. No coupling is observed for the para-fluoro derivative (74JCS(Pl)30). 

Since 21a is computed to be 3.8 kcal mol higher in energy than 21b, the larger activation barrier of the former cannot be attributed to fluorine stabilization of phenylnitrene. Instead, the ortho fluorines in 21a must destabilize the transition state for rearrangement. 

If additional stability can be gained, e.g. as a result of two ortho fluorines, transmetalation often occurs (middle and bottom). Occasionally (bottom) this can be suppressed by the right choice of reaction solvent [112]. 

Scheme 2.79 Representative syntheses of a variety of OF-reagents and the mechanism proposed for the selective electrophilic ortho fluorination of aromatic acetamides [178].

Scheme 2.85 Directed ortho-fluorination of phenols by N-fluoropyridinium-2-sulfonates [190],...

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