Sodium dithionite initiated fluoroalkylation of trimethoxybenzenes, mesitylene and pyrroles with BrCF2CF2Br

Article abstract of DOI:10.1016/j.jfluchem.2010.01.009

Sodium dithionite initiated reaction of 1,2-dibromotetrafluoroethane with 1,3,5-trimethoxybenzene (1a) in an acetonitrile-water mixture proceeded efficiently at ambient temperature to give 1-(2-bromotetrafluoroethyl)-2,4,6- trimethoxybenzene (2) almost quantitatively. Similar reaction with 1,2,3-trimethoxybenzene (1b) gave only reasonable yield of regioisomers of (2-bromotetrafluoroethyl)-trimethoxybenzenes 3 and 4 and small amount of a substitution product of the central trimethoxy group, 1-(2- bromotetrafluoroethyl)-2,6-dimethoxybenzene (5). The results of the reactions with mesithylene (6) gave complex mixtures from which, depending on the temperature and a mesithylene/BrCF₂CF₂Br ratio, the expected (2-bromotetrafluoroethyl)mesithylene (8) or a dimeric product, 4,4'-bis(2-bromo-1,1,2,2-tetrafluoroethyl)-1,3,5,1',3',5'- hexamethylbicyclohexyl-2,5,2',5'-tetraene (7), were isolated in a 18 and 13%, respectively. The reactions of BrCF₂CF₂Br with pyrrole (9) and 1-methylpyrrole (11) gave the respective alkylated compounds, 2-(2-bromotetrafluoroethyl)pyrrole (10) and 2-(2-bromotetrafluoroethyl)-1- methylpyrrole (12) in over 70% yields; the former was found to be fairly unstable. The reactivity of the terminal bromine atom in 1-(2- bromotetrafluoroethyl)-2,4,6-trimethoxybenzene (2) was also investigated.

Full text of DOI:10.1016/j.jfluchem.2010.01.009

Journal of Fluorine Chemistry 131 (2010) 746–750
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Sodium dithionite initiated fluoroalkylation of trimethoxybenzenes, mesitylene
and pyrroles with BrCF2CF2Br
*
Wojciech Dmowski , Krystyna Piasecka-Maciejewska
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka St. 44/52 P.O. Box 58, 01-224 Warsaw, Poland
A R T I C L E I N F O
A B S T R A C T
Article history:
Sodium dithionite initiated reaction of 1,2-dibromotetrafluoroethane with 1,3,5-trimethoxybenzene
(1a) in an acetonitrile–water mixture proceeded efficiently at ambient temperature to give 1-(2-
bromotetrafluoroethyl)-2,4,6-trimethoxybenzene (2) almost quantitatively. Similar reaction with 1,2,3-
trimethoxybenzene (1b) gave only reasonable yield of regioisomers of (2-bromotetrafluoroethyl)-
trimethoxybenzenes 3 and 4 and small amount of a substitution product of the central trimethoxy group,
1-(2-bromotetrafluoroethyl)-2,6-dimethoxybenzene (5). The reaction with mesitylene (6) gave complex
mixtures from which, depending on the temperature and a mesitylene/BrCF2CF2Br ratio, the expected
(2-bromotetrafluoroethyl)mesitylene (8) or a dimeric product, 4,40-bis(2-bromo-1,1,2,2-tetrafluor-
oethyl)-1,3,5,10,30,50-hexamethylbicyclohexyl-2,5,20,50-tetraene (7), were isolated in a yield of 18 and
13%, respectively. The reactions of BrCF2CF2Br with pyrrole (9) and 1-methylpyrrole (11) gave the
respective alkylated compounds, 2-(2-bromotetrafluoroethyl)pyrrole (10) and 2-(2-bromotetrafluor-
oethyl)-1-methylpyrrole (12) in over 70% yields; the former was found to be fairly unstable. The
reactivity of the terminal bromine atom in 1-(2-bromotetrafluoroethyl)-2,4,6-trimethoxybenzene (2)
was also investigated.
Received 15 December 2009
Received in revised form 27 January 2010
Accepted 28 January 2010
Available online 4 February 2010
Keywords:
1,2-Dibromotetrafluoroethane
Sodium dithionite
Radical reaction
Fluoroalkylation
Trimethoxybenzene
Mesitylene
Pyrrole
ß 2010 Elsevier B.V. All rights reserved.
1. Introduction
methane [13,14] to various electron-rich unsaturated compounds
but most attempts to alkylate aromatic and heteroaromatic
Since many years it has been known that perfluoroalkylations of
aromatic and heteroaromatic compounds, particularly when
activated by electron donating substituents, with perfluoroalkyl
iodides proceed readily in the presence of radical-anion sources
like dithionites or hydroxymethanesulphinates. Thus, phenolates,
anilines, amino-, methoxy- and methylbenzenes and pyrroles react
readily with perfluoroalkyl iodides at ambient temperature in a
water–acetonitrile, or water–dimethylsulphoxide solutions to give
perfluoroalkylated derivatives with 40 to over 80% yields [1–4].
Similarly they react with pyridines [5], quinolines [4] and
coumarines [6,7], however, in those cases, higher temperature is
usually required and yields of alkylated products are somewhat
lower. When more drastic reaction conditions were applied, i.e.
water-free dimethylsulphoxide, temperature of 75 8C and pro-
longed reaction time, perfluoroalkylation of N, S and O hetero-
aromatics and activated benzenes with long chain perfluoroalkyl
chlorides has also been reported [8]. In our laboratory, it has been
found that the Na2S2O4/acetonitrile/H2O system is also able to
promote addition of polyhaloalkanes, i.e.1-bromo-1-chloro-2,2,2-
compounds with these reagents were unsuccessful. The only
successful exceptions were reactions of 1-bromo-1-chloro-2,2,2-
trifluoroethane with 1,3,5-trimethoxybenzene and with pyrroles,
which resulted in coupling of one molecule of CF3CHClBr with two
molecules of the aromatic compound to give, respectively,
trifluoromethyl-bis(2,4,6-trimethoxyphenyl)methane [15] and 5-
(trifluoromethyl)-dipyrromethanes [16] in a 38–50% yields. In
those reactions both, Br and Cl atoms of CF3CHClBr were replaced
with an aromatic moiety.
1,2-Dibromotetrafluoroethane, which is readily prepared by
bubbling of tetrafluoroethene into liquid bromine, has received
considerable attention as fluoroalkylating agent. However, most of
the reported examples involved halophilic reactions of phenolates
and thiophenolates [17,18] or salts of heterocyclic amines [19,20]
which resulted in O-, S- and N-alkylations. Reported reactions of
BrCF2CF2Br with free thiophenols under free-radical conditions
(SO2, pyridine) also lead exclusively to S-alkylation [21], however
in the case of sterically hindered phenols, C-alkylation occurred
[22]. Some of the obtained bromotetrafluoro derivatives were
further funtionalized by nucleophilic replacement of the remain-
ing bromine atom [18–20].
trifluoroethane (Halothane1
)
[9–12] and dibromodifluoro-
Our results of the reactions of CF3CHClBr with the most
electron-rich aromatics, i.e. 1,3,5-trimethoxybenzene [15] and
pyrroles [16] in the Na2S2O4/CH3CN/H2O system, however did not
* Corresponding author. Fax: +48 22 632 66 81.
E-mail address: dmowski@icho.edu.pl (W. Dmowski).
0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2010.01.009

W. Dmowski, K. Piasecka-Maciejewska / Journal of Fluorine Chemistry 131 (2010) 746–750
747
result in the expected CF3CHCl-substituted aromatics, demon-
strated ability of this reaction system to promote C-alkylation of
the above-mentioned aromatics by fluorohaloalkanes other than
the perfluoroalkyl iodides. On this basis, and considering the
reported fact that even perfluoroalkyl chlorides are able to C-
alkylate activated aromatics [8], we undertake studies on the
reactions of polymethoxybenzenes, mesitylene and pyrroles with
1,2-dibromotetrafluoroethane, which hopefully should lead to C-
alkylated product (2-bro-motetrafluoroethyl) aromatics.
Scheme 1.
colourless fraction containing only compounds 3–5 in the same
ratio. It is worth to notice that formation of compound 5 involves
substitution of the central methoxy group in 1b by BrCF2CF2–,
which was fairly unexpected process.
The 1H and 19F NMR analysis of a mixture obtained from the
reaction of 1,2-dibromotetrafluoroethane with 1,4-dimethoxy-
benzene revealed mostly unreacted substrate and numerous
signals difficult to be assigned to any expected product. No
reaction at all occurred with anisole.
2. Results and discussion
1,2-Dibromotetrafluoroethane reacted readily with 1,3,5-tri-
methoxybenzene (1a) in the Na2S2O4/CH3CN/H2O system at
ambient temperature to give the expected 1-(2-bromotetrafluor-
oethyl)-2,4,6-trimethoxybenzene (2) almost quantitatively
(Scheme 1). The reaction proceeded cleanly, such that the crude
crystalline 2 was pure enough to give correct elemental analysis
without purification.
Results of the reaction of 1,2-dibromotetrafluoroethane with
mesitylene (6) (Scheme 3) depended on the conditions applied.
When it was carried out at ambient temperature with an excess of
BrCF2CF2Br, the product consisted of a mixture of colourless oils
and white crystalline precipitate. The precipitate was found by the
1H and 19F NMR spectra to be a dimeric product, 4,40-bis(2-bromo-
1,1,2,2-tetrafluoroethyl)-1,3,5,10,30,50-hexamethyl-bicyclohexyl-
2,5,20,50-tetraene (7) (13.3% isolated yield) and the oil consisted of
unreacted mesitylene and (2-bromotetrafluoroethyl)mesitylene
(8) in a 1:1 ratio. When an excess of mesitylene and elevated
The reaction with 1,2,3-trimethoxybenzene (1b) was much less
successful. Under the same conditions, and even when elevated
temperature and prolonged reaction time were applied, only
partial conversion of 1b was achieved to give a mixture containing
much of unreacted 1b (ca. 58%), the expected 1-(2-bromotetra-
fluoroethyl)-3,4,5-trimethoxybenzene (3), 1-(2-bromotetrafluor-
oethyl)-2,3,4-trimethoxybenzene (4) and 1-(2-bromotetrafluoro-
ethyl)-2,6-dimethoxybenzene (5) in a 4:3:1 ratio (NMR estimate)
and some dark impurities (Scheme 2). Subjecting the crude
reaction mixture to column chromatography allows to isolate
Scheme 2.
Scheme 3.

748
W. Dmowski, K. Piasecka-Maciejewska / Journal of Fluorine Chemistry 131 (2010) 746–750
aromatics with BrCF2CF2Br but this method could be applied only
to the most electron-rich compounds like polymethoxybenzenes,
pyrroles and mesitylene.
3. Experimental
Melting points were determined in
a capillary and are
uncorrected. 1H NMR, and 19F NMR spectra were recorded with
a Varian 400 spectrometer in CDCl3 solutions. Chemical shifts are
quoted in p.p.m. from internal TMS for 1H and from internal CFCl3
for 19F nuclei. Coupling constants (J) values are in Hz. Mass spectra
were obtained with an AMD-604 spectrometer.
Scheme 4.
temperature (70 8C) were applied, the resulting oil contained,
besides unreacted mesitylene, compound 8 (isolated by distilla-
tion, 18.5% yield) and complex mixture of higher molecular weight
compounds. The NMR analysis of the residual oil obtained after
removal of mesitylene and 8 (distillation) suggested that it
consisted of diastereo- and geometric-isomers of dimers of the
type 7. Mechanism of the formation of 7 and similar dimerization
of unsubstituted benzene [5] and 2,5-dimethylfurane [23] involves
direct coupling of intermediate fluoroalkylaryl radicals and is
somewhat different from that reported by us for the reactions of
CF3CHClBr with trimethoxybenzene and pyrroles [15,16]; in the
latter, the coupling is proceeded by elimination of HCl from one of
the interacting primary aryl radical.
Pyrrole (9) and N-methylpyrrole (11) reacted with BrCF2CF2Br
under standard conditions to give 2-(2-bromotetrafluoroethyl)-
substituted pyrroles 10 and 11 in good yields (Scheme 4).
Compound 10 was very unstable and quickly getting dark on
contact with the air and after storing overnight at the refrigerator
totally decomposed to form black tar. In contrast, N-methyl analog
12 was stable enough to be stored for a couple of weeks in the
refrigerator but also slowly decomposed at ambient temperature.
Both compounds, 11 and 12, could be distilled under reduced
pressure without decomposition.
3.1. 1-(2-Bromotetrafluoroethyl)-2,4,6-trimethoxybenzene (2)
Sodium dithionite (4.0 g [85%], 20 mmol), sodium hydrogen
carbonate (3.5 g, 40 mmol), 1,3,5-trimethoxybenzene (1a, 3.36 g,
20 mmol) and BrCF2CF2Br (7.2 g, 30 mmol) were added one by
one to an acetonitrile–water solution (1:1, 30 ml) at ambient
temperature (22 8C). The reaction mixture was vigorously
stirred and after few minutes slow gas evolution occurred
(CO2 formed by the reaction of SO2 with NaHCO3). No
exothermic effect was observed but thick precipitate of NaBr
was formed. After 4.5 h the reaction mixture was poured into
water (200 ml), insoluble crystalline precipitate was filtered off
and dried at ambient temperature under vacuum to give white
crystals. Yield: 6.5 g (18.7 mmol, 93.7%). M.p. 81–83 8C. Analy-
sis—found: C, 38.0; H, 3.3; Br, 23.1; F, 22.0%. Calculated for
C
11H11BrF4O3 (347.11): C, 38.1; H, 3.2; Br, 23.0; F, 21.9%. 1H
NMR: 3.80 (s, 2ꢀ CH3); 3.84 (s, CH3); 6.14 (s, 2Harom). 19F NMR:
3
3
ꢁ64.2 (t, JFF = 5.3 Hz, CF2); ꢁ99.7 (t, JFF = 5.3 Hz, CF2). MS (EI):
m/z (rel. int., ion): 348, 346 (12, 12, M+); 267 [11, (MꢁBr)+]; 217
[100, (MꢁCF2Br)+]; 139 (21, C7H7O3)+.
3.2. Reaction of BrCF2CF2Br with 1,2,3-trimethoxybenzene (1b)
The most stable and easy to prepare with high yield compound
2 was chosen to study the reactivity of its terminal bromine atom.
In contrast to the reported easy funtionalization of similar
compounds [18,20,21], compound 2 was found to be fairly
unreactive. The attempted substitution of bromine with fluorine
by treatment with 20% KOH/Bu4NBF4 in a water–benzene system
failed. Sulfinatodehalogenation of 2 in the presence of large excess
of 1,3,5-trimethoxybenzene did not give the expected 1,2-diaryl-
tetrafluoroethane. Also, sulfinatodehalogenation did not occurred
in the presence of ethyl vinyl ether, which is very susceptible to
attack by free radicals [9]. However, when compound 2 was
refluxed in an acetonitrile–water system with large excess of
Na2S2O4, reduction of the bromine atom or elimination of both Br
and F radicals occurred to give a mixture of 1-(1,1,2,2-tetrafluor-
oethyl)-2,4,6-trimethoxybenzene (13) and 1-(trifluoroethenyl)-
2,4,6-trimethoxybenzene (14) in a 1:3 ratio and 70% total yield
(Scheme 5). Low reactivity of the bromine atom in 2 is probably
due to high steric hindrance created by the neighboring methoxy
groups.
The reaction was carried out as described above (Section 3.1)
using the same amounts of reactants. Pouring the reaction mixture
into water resulted in precipitation of an oil, which was extracted
with diethyl ether and the extract was dried over anhydrous
MgSO4. Evaporation of the solvent gave dense, yellowish oil (6.4 g)
which was found by the 1H NMR analysis to consist of unreacted 1b
(58%), compounds 3 (21%), 4 (15%) and 5 (5%) and some impurities.
A part of the crude product (2.0 g) was subjected to column
chromatography to give colourless fraction (0.75 g, yield 34.5%)
containing only 3–5. Identical results were obtained when the
reaction was carried out in a sealed ampoule for 22 h at 74 8C (to
avoid high pressure of evolved CO2, NaHCO3 was replaced with
NaH2PO4).
1-(2-Bromotetrafluoroethyl)-3,4,5-trimethoxybenzene (3): 1H
NMR: 3.62 (s, 2ꢀ CH3); ca. 3.6 (CH3); 6.79 (s, 2Harom). 19F NMR:
3
3
ꢁ65.0 (t, JFF = 4.9 Hz, CF2); ꢁ107.7 (t, JFF = 4.9 Hz, CF2).
1-(2-Bromotetrafluoroethyl)-2,3,4,-trimethoxybenzene (4): 1H
3
NMR: ca. 3.5–3.7 (broad, 3ꢀ CH3); 6.72 (d, JHH = 9.0 Hz, 1Harom);
In conclusion, our experiments have shown that the Na2S2O4/
CH3CN/H2O system, in general, is able to promote C-alkylation of
7.22 (d, 3JHH = 9.0 Hz, 1Harom). 19F NMR: ꢁ64.0 (t, 3JFF = 5.0 Hz, CF2);
3
ꢁ104.1 (t, JFF = 5.0 Hz, CF2).
Scheme 5.

W. Dmowski, K. Piasecka-Maciejewska / Journal of Fluorine Chemistry 131 (2010) 746–750
749
1-(2-Bromotetrafluoroethyl)-2,6-dimethoxybenzene (5): 1H NMR:
30.6; N, 5.9%. Calculated for C6H4BrF4N (246.00): C, 29.3; H, 1.6; Br,
32.5; F, 30.9; N, 5.7%. 1H NMR: 6.30 (m, H-4); 6.62 (m, H-3); 6.95
(m, H-5); 8.57 (broad m, H-1). 19F NMR: ꢁ66.0 (t, 3JFF = 7.2 Hz, CF2);
3
ca. 3.5–3.7 (broad, 2ꢀ CH3); 6.15 (d, JHH = 8.4 Hz, 2Harom); 7.40
3
3
(t, JHH = 8.4 Hz, 1Harom). 19F NMR: ꢁ64.1 (t, JFF = 5.2 Hz, CF2);
ꢁ100.1 (t, 3JFF = 5.2 Hz, CF2).
ꢁ105.3 (t, JFF = 7.2 Hz, CF2). MS (EI): m/z (rel. int., ion): 247, 245
3
(18, 18, M+); 166 [13, (MꢁBr)+]; 147 [12, (MꢁBrF)+]; 116 [100,
(MꢁCF2Br)+]; 89 (12, C4H3F2+).
3.3. Reactions of BrCF2CF2Br with mesitylene (6)
3.3.1. With an excess of BrCF2CF2Br at ambient temperature
3.5. 2-(2-Bromotetrafluoroethyl)-1-methylpyrrole (12)
Sodium dithionite (4.0 g [85%], 20 mmol), sodium hydrogen
carbonate (2.0 g, 24 mmol), mesitylene (6, 2.4 g, 20 mmol) and
BrCF2CF2Br (10.4 g, 40 mmol) were added one by one to an
acetonitrile–water solution (1:1, 30 ml) and the reaction mixture
was vigorously stirred at ambient temperature (23 8C) for 20 h,
then poured into water (100 ml). The organic oily layer was
extracted with Et2O, the extract was washed with water and dried
over anhydrous MgSO4. Evaporation of the solvent gave a mixture
of colourless oil and fine, white precipitate. The precipitate was
filtered off, washed with ethanol and dried under vacuum to give
4,40-bis(2-bromo-1,1,2,2-tetrafluoroethyl)-1,3,5,10,30,50-hexam-
ethylbicyclohexyl-2,5,20,50-tetraene (7) as white powder. Yield:
0.81 g (2.7 mmol, 13.3%). M.p. 107 8C (rapid decomposition).
Analysis—found: C, 44.0; H, 4.1; Br, 26.6; F, 25.6%. Calculated for
Sodium dithionite (1.0 g [85%], 5 mmol), sodium hydrogen
carbonate (3.5 g, 40 mmol), 1-methylpyrrole (11, 1.62 g, 20 mmol,)
and BrCF2CF2Br (7.2 g, 30 mmol) were added one by one to an
acetonitrile–water solution (1:1, 30 ml) at ambient temperature
(22 8C). The reaction was carried out and worked up as in Section
3.5. Vacuum distillation of an oil (4.4 g) obtained after evaporation
of the ether gave 2-(2-bromotetrafluoroethyl)-1-methylpyrrole
(12) as colourless liquid. Yield: 3.75 g (14.4 mmol, 72%). B.p. 46 8C/
6 mmHg. Analysis—found: C, 32.3; H, 2.2; Br, 30.7; F, 39.5; N, 5.3%.
Calculated for C7H6BrF4N (260.03): C, 32.3; H, 2.3; Br, 30.7; F, 39.2;
N, 5.4%. 1H NMR: 3.73 (s, CH3); 6.15 (t, J = 3.3 Hz, H-4); 6.57 (m, H-
3
3); 6.73 (narrow m, H-5). 19F NMR: ꢁ64.1 (t, JFF = 6.8 Hz, CF2);
3
ꢁ101.5 (t, JFF = 6.8 Hz, CF2). MS (EI): m/z (rel. int., ion): 261, 259
C
22H24Br2F8 (600.23): C, 44.15; H, 4.0; Br, 26.4; F, 25.4%. 1H NMR:
(12, 12, M+); 180 [9, (MꢁBr)+]; 161 [7, (MꢁBrF)+]; 130 [100,
(MꢁCF2Br)+].
0.99 (s, 2ꢀ CH3); 1.82 (s, 4ꢀ CH3); 3.34 (t, 3JHF = 10.0 Hz, 2H); 5.76
3
(s, 4H). 19F NMR: ꢁ62.4 (s, CF2); ꢁ99.0 (d, JHF = 10.0 Hz).
The oil was found by the NMR analysis to be a 1:1 mixture of
unreacted mesitylene (6) and (2-bromotetrafluoroethyl)mesity-
lene (8) which were not separated.
3.6. Reaction of 1-(2-bromotetrafluoroethyl)-2,4,6-
trimethoxybenzene (2) with an excess of Na2S2O4
Compound 2 (3.47 g, 10 mmol), sodium dithionite (10.0 g [85%],
50 mmol), sodium hydrogen carbonate (4.5 g, 54 mmol), acetoni-
trile (20 ml) and water (40 ml) were refluxed for 9 h. Acetonitrile
was removed on a rotary evaporator and the insoluble white solid
was filtered off, washed with large amount of cold water (removal
of inorganic salts) and dried over NaOH under vacuum. The NMR,
GC–MS and HMRS analyses have shown that the solid consist of 1-
(1,1,2,2-tetrafluoroethyl)-2,4,6-trimethoxybenzene (13) 1-(tri-
fluoroethenyl)-2,4,6-trimethoxybenzene (14) in a 1:3 ratio. Total
yield: 2.0 g (7 mmol, 70%).
3.3.2. With an excess of mesitylene at elevated temperature
Sodium dithionite (4.0 g [85%], 20 mmol), disodium hydrogen
phosphate (4.3 g, 30 mmol), mesitylene (6, 7.2 g, 60 mmol),
BrCF2CF2Br (5.2 g, 20 mmol) and acetonitrile–water solution
(1:1, 30 ml) were placed in a firmly closed reaction flask (the
stopcock was wired). The reaction mixture was vigorously stirred
at 70 8C for 2 h (all inorganic salts dissolved), then for 22 h at
ambient temperature. Addition of water (100 ml) to the reaction
mixture caused formation of bottom organic layer which was
separated and the water layer was extracted with ether (2ꢀ 30 ml).
The extract and the main organic layer were combined, washed
with brine (2ꢀ 70 ml) and dried over anhydrous MgSO4. Vacuum
distillation of an oil (8.4 g) obtained after evaporation of the ether
allowed to isolate (2-bromotetrafluoroethyl)mesitylene (8) (1.1 g,
3.7 mmol, 18.5% in respect to BrCF2CF2Br) as colourless oil. B.p. 54–
56 8C/2 mmHg. Analysis—found: C, 44.5; H, 3.7; Br, 26.3; F, 25.2%.
Calculated for C11H11BrF4 (299.11): C, 44.15; H, 4.0; Br, 26.4; F,
1-(1,1,2,2-Tetrafluoroethyl)-2,4,6-trimethoxybenzene (13): 1H
NMR: 3.82 (s, 2ꢀ CH3); 3.83 (s, CH3); 6.15 (s, 2Harom); 6.31 (tt,
3
2JHF = 54.1 Hz, JHF = 5.5 Hz, CF2H). 19F NMR: ꢁ110.6 (td,
2
3JFF = 9.5 Hz and 5.5 Hz, –CF2–); ꢁ137.7 (dt, JHF = 54.1 Hz,
3JFF = 9.5 Hz, CF2H). GC–MS (EI): m/z (rel. int., ion): 268 (25, M+);
217 [100, (MꢁHF–OCH3)+]; 139 (40, C7H7O3+); 101 (6, C2F2H+); 51
(4, CF2H)+. HRMS: 268.07153. Calculated for H11H12F4O3:
268.07226.
25.4%. 1H NMR: 2.28 (s, CH3); 2.42 (t, JHF = 4.7 Hz, 2ꢀ CH3); 6.91
1-(Trifluoroethenyl)-2,4,6-trimethoxybenzene (14): 1H NMR:
3.82 (s, 2ꢀ CH3); 3.84 (s, CH3); 6.11 (s, 2Harom). 19F NMR:
5
3
(narrow m, 2Harom). 19F NMR: ꢁ63.0 (t, FFF = 4.2 Hz, CF2); ꢁ95.5
2
3
(nonet, average JHF and FF = 4.4 Hz, CF2). MS (EI): m/z (rel. int., ion):
300, 298 (36, 36, M+); 219 [17, (MꢁBr)+]; 169 [100, (MꢁCF2Br)+];
119 [12, (MꢁC2F4Br)+].
ꢁ103.1 (dd, JFF = 74.4 Hz, JFF = 26.5 Hz, 55CF2); ꢁ117.9 (dd,
2JFF = 74.4 Hz, JFF = 117.0 Hz, 55CF2); ꢁ163.8 (dd, JFF = 117.0 Hz,
3JFF = 26.5 Hz, –CF55). GC–MS (EI): m/z (rel. int., ion): 248 (70, M+);
233 [100, (MꢁCH3)+]; 218 [10, (Mꢁ2CH3)+]; 203 [20, (Mꢁ3CH3)+];
139 (40, C7H7O3+); 81 (20, C2F3+). HMRS: 248.06649. Calculated for
3
3
3.4. 2-(2-Bromotetrafluoroethyl)pyrrole (10)
C11H11F3O3: 248.06603.
Sodium dithionite (1.0 g [85%], 5 mmol), sodium hydrogen
carbonate (3.5 g, 42 mmol), freshly distilled pyrrole (9, 1.34 g,
20 mmol,) and BrCF2CF2Br (7.2 g, 30 mmol) were added one by one
to an acetonitrile–water solution (1:1, 30 ml) at ambient
temperature (22 8C). The reaction mixture was vigorously stirred
and after few minutes the CO2 evolution occurred with slight
exothermic effect. The gas evolution ceased after 3 h, then the
reaction mixture was diluted with water (100 ml) and worked up
as in Section 3.3.2. Vacuum distillation of an oil (5.0 g) obtained
after evaporation of the ether gave 2-(2-bromotetrafluoroethyl)-
pyrrole (10) as colourless liquid. Yield: 3.6 g (14.6 mmol, 73%). B.p.
32–36 8C/6 mmHg. Analysis—found: C, 29.8; H, 1.8; Br, 32.2; F,
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