Reaction with hexafluorobenzene

In the reaction with hexafluorobenzene at 40"C exclusive 1,4-addition to give 18 is observed. In addition to higher regioselectivity, perfluoro-fcrf-butyl hypofluorite has higher reactivity as a reagent compared to trifluoromethyl hypofluorite (see Section 6.1.1.).14... 

Interestingly, the hydrogen/deuterium exchange of both (M — H) ions with D20 is not observed to go to completion, but stops after a certain reaction time. Evidence has been presented that this phenomenon is due to an irreversible isomerization of the (M — H) ions to the enolate anion [13] of 3-methylbutanal, which also gives the same product ions in reactions with hexafluorobenzene (Peerboom et al., 1985). The results obtained clearly point to a complex mixture of interconverting ion structures as shown in (67a-e). 

The nature of the transient qiecies formed from the reactitm of Oaq whh perfluorobenzene can be determined frtim electron transfer studies whh a suitable electron acceptor. Based on these studies h was concluded diat the reaction of eaq with perfluoroacett henone or perfluorobenzaldd e formed radical anions whereas the reaction with hexafluorobenzene, pentafluon hmol or pentafluoroaniline resulted in the frxmation of a radical species vtidi fluoride ion eliminatioa Similarly, the reaction of electron with all rl halides (RX) lead to the formation of the allQrl radical and the halide ioa... 

Write equations describing the addition-elimination mechanism for the reaction of hexafluorobenzene with sodium methoxide clearly showing the structure of the rate determining intermediate j... 

The most common types of aryl halides in nucleophilic aromatic substitutions are those that bear- o- or p-nitro substituents. Among other classes of reactive aryl halides, a few merit special consideration. One class includes highly fluorinated aromatic compounds such as hexafluorobenzene, which undergoes substitution of one of its fluorines on reaction with nucleophiles such as sodium methoxide. 

The authors carried out theoretical calculations on this system as well as on the [ (PMej) ] system to compare their reactivity with hexafluorobenzene. They found that the barrier for [ (liPr) ] is approximately 10 kJ/mol lower in energy than the corresponding barrier for the phosphine-bearing system. This value was in agreement with the different reactivity of both complexes but could not fully explain the large difference in reaction times. Density functional Theory (DFT) calculations also showed that the trans product is more stable than the cis product (total energies are respectively -130.9 and 91.1 kJ/mol), which was in agreement with the experimental values. 

Reaction of hexafluorobenzene with MeIr(PEt3)3 results in C—F and P—C bond cleavage and P—F bond formation, according to reaction Scheme 28.504 An X-ray crystallographic study of (310) reveals a distorted square-planar arrangement of Ir. 

Figure 3. Effect of water on the reaction of hexafluorobenzene and bisphenol-A in chlorobenzene in the presence of 18 crown-6 catalyst. Products of the catalyzed reaction were oligomeric materials. No reaction is observed under the experimental conditions in the absence of the 18-crown--6 catalyst. (Reproduced with permission from reference 14, Copyright 1985 John Wiley.)...

The reaction of the carbanion derived from diethyl methylphosphonate with perhalogenated aromatics may result in substitution of halide to yield perhaloaryl(hetaryl)methylphosphonates, which can be converted into tris- or bis-(perhaloaryl)methanes. Displacement of fluoride ion has been reported in the reaction of dimethoxycarbene with l-fluoro-2,4-dinitrobenzene and with hexafluorobenzene. The hydrodehalogenation of halogenated aryl ketones may be facilitated using hydrogen over a Pt/C catalyst. " ... 

Three recent papers directed toward the reaction of elemental fluorine with hexafluorobenzene (71), decafluorohexane (72), and pentafluoro-... 

A mixture of tetrafluoroethene (2.45 g, 24.5 mmol), 02 (24.5 mmol) and 03 (0.03 mmol) was condensed in a Pyrex tube (33 ml) with a long capillary neck containing hexafluorobenzene (8.3 g). After 5 d reaction in (he dark at 15 C, the ampule was opened and the volatile products were analyzed and separated by GC [He as carrier gas, —9 C, bis(2-ethylhcxyl) sebacate on kieselguhrl yields 17 (0.67 g, 24%), 21 (0.38 g, 23%). A highly viscous residue that contained 19 (1.5 g) was diluted with hexafluorobenzene and treated with a slight excess of 57% HI (1 part) and glacial HOAc (10 parts), usually at rt. The whole apparatus was swept with He and the C02 evolved during the reduction was absorbed by standard Ba(OH)2. 

The preparation of perfluoroazepines is more facile. Hexafluoro-l//-azepine-l-carbonitrile (6a) is prepared by the reaction of hexafluorobenzene with cyanonitrcne.15 Likewise, the 1-ethoxycarbonyl derivative 6 b is prepared in moderate yield by the reaction of hexafluorobenzene with ethoxycarbonylnitrene.16 In each case, a benzoazirine intermediate is presumably involved, which isomerizes to the azepine structure. Perfluoroazepines 6 isomerize photolytically to the corresponding 2-azabicyclo[3.2.0]hepta-3,6-dicncs 7 in high yield.17 Azepine 6c is obtained from 6a by acid hydrolysis.17... 

The primary ortho adducts formed from benzene derivatives and acetylenes are derivatives of bicyclo[4.2.0]octa-2,4,7-triene. These products usually are not isolated but isomerize during the irradiation to cyclooctatetraenes [58,59,68,72], From combinations of hexafluorobenzene and pentafluoroalkoxybenzenes with various disubstituted acetylenes, however, the isolation of relative stable primary ortho adducts has been reported [65-67], In Scheme 46, the products of the photochemical reaction of hexafluorobenzene with but-2-yne are shown [67],... 

Alternatively, tetrafluoroanthracene could form by the reaction of benzyne with tetrafluoronaphthalene. In that case, however, some difluoroanthracene should also form by 1,4-addition of benzyne to the fluorinated ring. No difluoroanthracene or difluoroanthracene-d8 was found in the products from the reactions of hexafluorobenzene with acetylene and acetylene-d2, respectively. 

The reaction of hexafluorobenzene (179) with pyrrole anion in THF for 24 h leads to the /7-disubstitution product (38%) on nitrogen, with successively lesser amounts of the higher polysubstitution products228. The reaction of 179 with pyrazole anion (180) (6 h) gave quantitatively the N-hexasubstituted product 181. The reaction was partially inhibited by ra-DNB and 75% of 181 and 17% of the /7-disubstitution product 182 were formed in 24 h (equation 124)228. 

Hexafluorobenzene and pentafluorotellurium hypofluorite produced, after four days at 25°, a 50% yield of hexafluorocyclo-hexa-2,5-dien-l-yloxy tellurium pentafluoride3. Similar reactions with pentafluorotellurium hypochlorite gave much lower yields of addition products2. 

Hexapyrrol-l-ylbenzene and octapyrrol-1-ylnaphthalene can be obtained in high yields by the reaction of sodium pyrrolide with hexafluorobenzene or octafluoronaphthalene, respectively, at room temperature in DMF <1996JOC9012>. 

Fluoro-substituted annotated five-membered heterocycles are available via stepwise nucleophilic displacement reactions of perfluorinated or polyfluorinated aromatic compounds by 1,3-dinucleophiles. On reaction of hexafluorobenzene with the sodium salt of ethyl acetoacetate the 3-ethoxycarbonyl-2-methylcumarone is formed [64DOK( 158)926 69KGS778] (Scheme 29). 

The extremely electrophilic nature of bis(trifluoromethyl)carbene has already been illustrated by the formation of addition products, even with hexafluorobenzene [83] (Section lllB), and the high reactivity results in more side-reactions, such as insertion into C—H bonds, than with difluorocarbene (Figure 6.62). 

Sequential functionalization of pyrazole-l-oxides via regioselective metallation led to the synthesis of 3,4,5-trisub-stituted-l-hydroxypyrazoles <2002JOC3904>. 3-Acylated-2-(4-methoxybenzyl)-2//-pyrazole 1-oxides were formed by the reaction between a 3-magnesium 2//-pyrazole-l-oxide and acid chlorides <2002J(P1)428>. 3-Arylated-l-hydroxypyrazoles were synthesized from 3-metallated-pyrazole 1-oxides <2001JOC8654>. The reaction between hexafluorobenzene and the anion of 1-hydroxypyrazole affords a mixture of the products of bis-, tetrakis-, and hexakis-substitution <2004ARK100>. In the case of hexakis(bromomethyl)benzene, its reaction with 1-hydroxy-pyrazole leads to the hexakis-substituted product. 

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