Fluorobenzene derivatives

Desilylation-electrophilic substitution of trimethylsilylbenzenes provides a route to a number of mefa-substituted fluorobenzene derivatives such as 3-fluoro-acetophenone, which is unobtainable under normal Friedel-Crafts conditions [36] (equation 25). 

Aryl halide compounds such as fluorobenzene derivatives can be used to form covalent bonds with amine-containing molecules like proteins. The reactivity of aryl halides, however, is not totally specific for amines. Other nucleophiles such as thiol, imidazolyl, and phenolate groups of amino acid side chains also can react (Zahn and Meinhoffer, 1958). Conjugates formed with sulfhydryl groups are reversible by cleaving with an excess of thiol (Shaltiel, 1967). 

Sulfhydryl Compound Fluorobenzene Derivative Aryl Thioether Bond... 

Knowledge was accumulated systematically from the start of the present century, and has been summarized.9 A major contribution was made by Holleman and his group in the Netherlands in the period up to 1915. Various fluorobenzene derivatives having one or more substituents (N02, NH2, Me, C02H, OMe, SOsH or halo) were made and orientated. The ratio of isomers formed in the nitration of fluorobenzene was determined (mainly para some ortho). Also, fluorobenzene was itself resistant to attack by nucleophiles, but if a nitro group was present, particularly in the para position, fluorine was replaced much more readily. 

Decomposition of the diazonium trifluorotris(perfluoroalkyl)phosphates proceeds mildly, without formation of tars (since no strong Lewis acid evolves), and with high yields of the substituted fluorobenzenes. For example, l-fluoro-4-nitrobenzene is obtained in a far better yield (82%) than from 4-nitrobenzenediazonium hexafluorophosphate or tetrafluoroborate [cf. formation of 2 (R = 4-N02)]. The coproduced difluorotris(perfluoroalkyl)-A5-phosphanes are not soluble in the resulting fluorobenzene derivatives and, because of their high density, form a lower layer which is readily separated. Thus, these difluoro-25-phosphanes can be regenerated quantitatively and used repeatedly. 

Koerts, J., Velraeds, M.M.C., Soffers, A.E.M.F., Vervoort, J., and Rietjens, I.M.C.M., Influence of substituents in fluorobenzene derivatives on the cytochrome P450-catalysed hydroxylation at the adjacent ortho aromatic carbon center, Chem. Res. Toxicol., 10, 279-288, 1997. 

Arylpiperazines can be prepared in a one-pot procedure by ipso SNAr of piperazine derivatives with //6-fluoroarene complexes la, 33a,b,d. Indeed, piperazine derivatives react with fluorobenzene derivatives in DMSO in the presence of K2CO3 at 80 °C to give, after 2.5 h, complexes 3m and 3k (Nu = piperazine) in good yields (Scheme 18) [34]. Piperazine itself may be used as a nucleophile and gives the monoarylpiperazine derivative uncontaminated by any symmetrical N,N -bis(aryl)piperazine, allowing the direct preparation of unprotected compounds. 

Taft and co-workers solvent polarity parameter P, based on solvent effects on F-nmr shielding in fluorobenzene derivatives (159) ... 

Taft et al [Ta 63] introduced solvent scales based on the NMR chemical shifts of meta and pnra-substituted fluorobenzene derivatives. However, the values of the factors obtained from these measurements are influenced by the interactions of both the substituent and the fluorine atom with the solvent. Later modifications of this method led, however, to the general solvent polarity scale of Abboud et al [Ab 77, 79, Ko 77]. 

The intermolecular version of the Scholl reaction is much less prevalent in the literature due to the difficulty in controlling the formation of the desired products. Bushby and co-workers have used an intermolecular version of the Scholl reaction in efforts toward the synthesis of chirally discotic liquid crystals featuring the triphenylene nucleus. The fluorobenzene derivative 20 was coupled with the symmetric biphenyl 19 to... 

Gas Chromatographic Assay with Electron-Capture Detection of the Penta-fluorobenzene Derivative J. Chromatogr. 163(2) 135-142 (1979) ... 

V( Fax, Fax) values can be very large due to the through-space interactions of sterically close diaxial fluorine atoms. On the other hand, in aromatic fluorobenzene derivatives the V( F, F) coupling constant provides only limited structural information the V( F, F), V( F, F) and V( F, F) coupling constants are often very similar and they can range from 18 to 20, 0 to 20 and 5 to 18 Hz, respectively. 

---