Remarkable Effect of Water on Functionalization of the Phenyl Ring in Methyl-Substituted Benzene Derivatives with F-TEDA-BF 4 (original) (raw)
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Journal of Fluorine Chemistry, 1992
Functionalization of mono-and d&substituted benzene derivative with CsSO,F has been modulated by substituents on the benzene ring. a-Hydroxyalkylbenzenes, with a deactivated ring, were oxidized to phenones, while fluorodealkylation was achieved in high yield when electron-donating groups were present in a pura position. Electron-withdrawing substituents favoured chain fluorofunctionalization in alkylbenzenes, while ring fluorination was found exclusively in acylamino-derivatized alkylbenzenes; fluoro-addition products were formed in the case of p-alkoxy-substituted alkylbenzene derivatives.
The role of F–N reagent and reaction conditions on fluoro functionalisation of substituted phenols
Tetrahedron, 2006
The effect of steric interactions on the regioselectivity of fluorination of para alkyl substituted phenols was investigated and the strong effect of size of the alkyl substituent, the structure of the F-N reagent and the solvent on the site of fluorination was established. The course of reaction obeyed a second order rate equation, while the fluorination process required higher DH s activation than oxidation or oxidative demethylation. Solvent polarity variations had a small effect on the rate of functionalisation, while an excellent Hammett correlation with r C ZK2.3 was determined. q
Journal of Fluorine Chemistry, 1999
Treatment of 1,3,5-trimethoxybenzene with one molar equivalence of 1-chloromethyl-4-¯uoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetra¯uoroborate) (F-TEDA-BF 4 ) under mild conditions (À40 to 208C) in acetonitrile gave mainly 2-¯uoro-1,3,5-trimethoxybenzene (62% yield; all product yields quoted refer to isolated pure materials, unless otherwise stated) and some 4,4-di¯uoro-3,5dimethoxycyclohexa-2,5-dien-1-one (13% yield), the structural parameters of which were determined by X-ray crystallography. Evidence that the minor product arose via¯uorodemethylation of the 2-¯uoro-1,3,5-trimethoxybenzene formed ®rst was obtained in a separate experiment involving this¯uoroaromatic compound and F-TEDA-BF 4 as the sole reactants. Treatment of 1,3,5-trimethoxybenzene with a two molar equivalence of F-TEDA-BF 4 in acetonitrile (at À20 to 208C) produced only 4,4-di¯uoro-3,5-dimethoxycyclohexa-2,5-dien-1one (>50% yield), a conversion which was unaffected by carrying out the reaction in either aqueous acetonitrile (20 vol% H 2 O) or neat water. Treatment of 2,4,6-trimethoxytoluene with a two-molar equivalence of F-TEDA-BF 4 in acetonitrile between À20 and 208C gave the¯uorodemethylation product 4-¯uoro-3,5-dimethoxy-4-methylcyclohexa-2,5-dien-1-one in 81% yield. # 1999 Elsevier Science S.A. All rights reserved.
Arkivoc, 2004
The 3,4-dialkylsubstituted phenols: 3,4-dimethylphenol, 5-indanol, and 5,6,7,8-tetrahydro-2naphthol were used as target molecules for fluorination with the N-fluoro-1,4diazoniabicyclo[2.2.2]octane salt analogues Selectfluor TM F-TEDA and Accufluor TM NFTh. 4-Fluoro-3,4-dialkylcyclohexa-2,5-dienone derivatives, as the result of an addition-elimination process, were the main, and 2-fluoro-and 6-fluoro-3,4-dialkylphenols derivatives resulting from a substitution reaction, the minor products of the fluorination process. The type of transformation was found to be independent of the structure of starting material and reagent, while these two parameters were important for the regioselectivity of the substitution reaction. The effect of the solvent on these reactions was evaluated, second order kinetics for the fluorination with F-TEDA in MeCN was established, rate konstants k 2 were measured, and thermodynamic parameters for the transition state (∆H * , ∆S * , and ∆G *) determined. A reaction pathway postulating a SET process as the key step was proposed.
Physical Chemistry Chemical Physics, 2001
The introduction of a fluoro-substituent in the phenyl ring of 4-(1-azetidinyl)benzonitrile (P4C) leads to smaller fluorescence quantum yields F f and shorter decay times t in alkane solvents (cyclopentane, n-hexadecane, n-hexane and 2-methylpentane). In cyclopentane at 25 C, F f and t equal 0.02 and 0.14 ns for 2-fluoro-4-(1-azetidinyl)benzonitrile (P4CF2) and 0.11 and 0.85 ns for 3-fluoro-4-(1-azetidinyl)benzonitrile (P4CF3), as compared with 0.27 and 4.55 ns for P4C. The fluorescence originates from a locally excited (LE) state and dual fluorescence due to intramolecular charge transfer is not observed for the three aminobenzonitriles at any temperature in the alkane solvents. By measuring the yields of intersystem crossing F ISC , it follows that this enhancement of the radiationless deactivation of the first excited singlet state S 1 is due to thermally activated internal conversion (IC). The IC yield F IC in cyclopentane at 25 C, as an example, is considerably larger for P4CF2 (0.93) than for P4CF3 (0.35) and of minor importance for P4C (0.03). The IC activation energies E IC of P4CF2 (12.6 kJ mol À1), P4CF3 (19.3 kJ mol À1) and P4C (38.1 kJ mol À1) in cyclopentane were determined by fitting t measured as a function of temperature, together with data for F f and F ISC. Similar E IC values were obtained in n-hexane and n-hexadecane. These data show that the increase in IC efficiency from P4C via P4CF3 to P4CF2 is caused by a decrease in E IC. The radiative rate constants k f in cyclopentane of P4CF2 and P4CF3 are about twice that of P4C, probably due to the mixing of the S 2 (1 L a , CT) and S 1 (1 L b) states of P4C caused by the molecular asymmetry introduced by the F-substituents. It is assumed that the lowering of the IC barriers in P4CF2 and P4CF3 is governed by an F-substituent-dependent difference in the energies of the molecular configuration of the azetidinylbenzonitriles that can be reached in S 1 as compared with those in S 0 .
Synthesis and 1H and 13C NMR spectra of 7-fluoro-, 9-fluoro- and 11-fluoro-benzo[b]fluoranthenes
Journal of Fluorine Chemistry, 1984
We have synthesized 7-fluoro-, 9-fluoro-and ll-fluorobenzo[blfluoranthene as part of a study designed to locate the molecular sites involved in the metabolic activation of the carcinogenic parent hydrocarbon. Analysis of the proton NMR spectra reveals the effect of fluorine substitution to be almost entirely localized in the substituted ring, the principal exception being a strong deshielding of opposing protons in sterically crowded sites (i.e., peri or pseudo-bay regions).