With Replacement of two Fluorine Atoms

Fluoroalkoxy tellurium trifluorides and )V,A -bis[trimethylsilyl]benzenesulfonamides in refluxing benzene form fluoroalkoxy benzenesulfonimido tellurium fluorides.  

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With Replacement of two Fluorine Atoms and two Fluoroalkoxy Groups... 

Receptor for naphthalene diimide guest with efficient quenching of prophyrin fluorescence was obtained by replacement of two fluorine atoms in compound 169 by n-pentylamine [118]. Perfluoroalkyl-s-triazines 170 can be used as high-temperature fluids (Scheme 71) [119],... 

Diazoketones react with trifluoromcthyl hypofluorite to give a mixture of a,a-difluoro ketones and o-fluoro-a-trifluoromethoxy ketones [70, 71] With elemental fluorine, two fluorine atoms replace the nitrogen in both diazoketones and unactivated diazo eompounds [70, 72, 73] (equation 9)... 

All the above examples refer to thiophenes containing functional groups indifferent to the presence of butyllithium. In reactions with reagents in an equimolar ratio, it is highly probable that only one of the fluorine atoms at the double bond of cyclene will be replaced. For example, the target product 26 (Scheme 8) was prepared by either a one-pot reaction in the presence of a twofold excess of lithium derivative 24 with respect to per-fluorocyclopentene or in two steps including the isolation of monofluoride 25 (99IZV10n). 

An unusual six-electron cycloaddition could be observed in the reaction of CgQpjg with tetrathiafulvalene (TTF) [70], TTF is not added to one of the free double bonds but replaces two of the fluorine atoms in a way that leaves the CgQpjg moiety, whose structure is described above (Figure 9.1). Under loss of F2 the product Cjq Fi6(TTF) is formed (Figure 9.7). 

Only a few qui nones react with sulfur tetrafluoride in the normal way by replacing each carbonyl group by two fluorine atoms. The examples are 9,10-anthraquinone (l),41 phenanthrene-9,10-quinone (2),100 and acenaphthoquinone and its substituted derivatives 3.101102 The reactions proceed at 150-300 C, preferably in the presence of anhydrous hydrogen fluoride. 

Terminal perfluoroolefins have two fluorine atoms at the double bond. The carbon atoms of the latter bear a significant positive charge, and the nucleophilic agents easily replace the fluorine atoms at the multiple bond. The reactions of binucleophilic reagents with terminal perfluoroolefins form heterocyclic systems. The first step of the reaction involves a nucleophilic attack at the carbon atom of the double bond, generating a carbanion. The latter is stabilized by elimination of the fluoride ion and formation of a new double bond. Subsequent cyclization by the intramolecular attack of the nucleophilic center at the double bond leads to the formation of a heterocyclic system. For example, when a reaction mixture of hexafluoropropylene and sodium dialkylaminodithiocarbamate in dimethylacetamide is heated with aqueous sodium tetraphenylborate, one obtains the tetraphenylborate salt of 2-dialkylamino-4-trifluoromethyl-4,5-difluoro-l,3-dithiolan-2-yl (78JFC(12)193). This compound is formed by intramolecular cyclization of the S-nucleophilic center. 

Probably the most versatile reagent for one-step exchange of hydroxy groups by fluorine, and for many other conversions, is sulfur tetrafluoride SF4 [125]. Sulfur tetrafluoride first converts the alcohol into a covalent intermediate with a nucleofugic group which is subsequently replaced by a liberated fluoride ion, with inversion (S>j2 mechanism). The sulfur tetrafluoride is converted into sulfonyl fluoride, only two fluorine atoms are used for the reaction. 

Each of the two fluorine atoms in the fluorine molecule is a strong electron acceptor. This property is responsible for the partial electrophilic behavior of elemental fluorine under certain circumstances and selective fluorinations of organic compounds with elemental fluorine have been reviewed on several occasions12 84,85. Tertiary hydrogens in steroids are preferably replaced by fluorine with retention of configuration86 87. 

As in the reactions of N3P3F6 with methyl-lithium, replacement of the first two fluorine atoms in the same substrate by phenylethynyl-lithium occurs by a predominantly geminal reaction path ... 

The coupling reaction of arylsilanes with aryl iodides is also mediated by a palladium catalyst and a fluoride ion.f " Optimized reaction conditions are as follows (i) two fluorine atoms on silicon are required (ii) an ethyl or propyl group as a dummy alkyl ligand is preferred, because a methyl group competitively participates in the crosscoupling reaction and (iii) TBAF, a highly effective fluoride ion source, can be replaced by inexpensive KF. Various unsymmetrical biaryls are synthesized under the conditions (Scheme 10). 

Nucleophilic substitution of tetrafluorophthalonitrile (29) with the benzenethiolate anion gives replacement of two or four fluorine atoms, but not the nitrile groups. 

Fluorine substitution of methanesulfonamides also leads to an additive decrease in the p of the NH proton. As shown in Table 3, the decrease in pK is approximately 1.47 units per fluorine substituent and is independent of the R-group bound to nitrogen [90]. The linearity observed in this trend is postulated to be due to the small steiic changes associated with replacing hydrogen by fluorine and the fact that fluorine substitution is somewhat remote (two atoms away from the acidic site) [90]. In the case of fluoroacetic acids, the decrease in p due to fluorine substitution is not additive the p T of acetic acid=4.76 fluoroacetic acid=2.59 difluoroacetic acid= 1.33 and trifluoroacetic acid=0.50 [91]. 

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