N-(2-bromotetrafluoroethyl) derivatives of five-membered nitrogen-containing heterocycles

Article abstract of DOI:10.1016/j.jfluchem.2005.07.005

The synthesis of N-(2-bromotetrafluoroethyl) derivatives of five-membered heterocycles containing one to three nitrogen atom(s) in the ring has been carried out. The reactions of these compounds with various sulfur-containing nucleophiles have been studie

Full text of DOI:10.1016/j.jfluchem.2005.07.005

Journal of Fluorine Chemistry 126 (2005) 1342–1346
www.elsevier.com/locate/fluor
N-(2-bromotetrafluoroethyl) derivatives of five-membered
nitrogen-containing heterocycles
*
Kirill I. Petko, Taras M. Sokolenko, Andreii V. Bezdudny, Lev M. Yagupolskii
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmans’ka st. 5, 02094 Kyiv, Ukraine
Received 18 May 2005; received in revised form 12 July 2005; accepted 21 July 2005
Available online 21 September 2005
Abstract
The synthesis of N-(2-bromotetrafluoroethyl) derivatives of five-membered heterocycles containing one to three nitrogen atom(s) in the
ring has been carried out. The reactions of these compounds with various sulfur-containing nucleophiles have been studied, and corresponding
sulfides, sulfones and sulfinic acid salts were obtained.
# 2005 Elsevier B.V. All rights reserved.
Keywords: 1,2-Dibromotetrafluoroethane; Nitrogen-containing heterocycles
1. Introduction
2. Results and discussion
Derivatives of five-membered heterocycles—pyrrole,
imidazole, pyrazole, and triazole are important intermediate
products in syntheses of biological active compounds. Some
heterocyclic compounds with the difluoromethyl group near
the nitrogen atom, such as sulfentrazole [1] have the
practical use as herbicides now.
The heterocycles, containing one to three ring nitrogen
atoms, namely pyrrole, imidazole, benzimidazole, pyrazole,
and 1,2,4-triazol 1a–e were chosen as the subjects for the
work (Scheme 1).
The reactions of 1,2-dibromotetrafluoroethane with
phenols, thiophenoles [14,15], and secondary amines have
been studied earlier. In the latter case N-(2-bromotetra-
fluoroethyl) derivatives were found to hydrolyze easily,
which hindered the isolation of the pure compounds [16].
In contrast to alkylamines with difluoromethylene group at
nitrogen, the corresponding N-polyfluoroalkylated nitrogen-
containing heterocycles are more stable to nucleophilic
substitution of fluorine at the a-position to the nitrogen atom
of the heterocycle owing to the involvement of the nitrogen
lone pair in the aromatic six-electron p-system. Therefore,
compounds 2a–e, as well as other similar compounds, are
hydrolytically stable.
The heterocyclic compounds with CF2H [2–4],
CF2CF2H, CF2CFClH [5–9], CF2Br [10,11], and CF3
[12,13] groups attached to nitrogen have been obtained
earlier. The N-2-(bromotetrafluoroethyl) derivatives of five-
membered heterocycles are unstudied. In this work we have
studied the possibility to introduce the 2-bromotetrafluoro-
ethyl group at the ring nitrogen atom, by the reaction of
corresponding heterocyclic sodium derivatives with 1,2-
dibromotetrafluoroethane and functionalization of the
terminal carbon. The bromofluoroalkanes are banned
products under the Montreal Protocol and its successors.
But at the present time the destruction problem of such
products exist. So, a chemical way to use bromofluoroalk-
anes (instead of simply destroying them) is an actual
problem.
The reaction of imidazole salts with dibromodifluor-
omethane studied earlier showed that the sodium derivative
gives a low yield of desired product [10], whereas use a
imidazolyl potassium yields 85% of N-bromodifluoro-
methylimidazole [11]. Evidently using a bulky counter
ion leads to formation of a more sterically separated ion pair.
Because of this the nucleophilic centre becomes more
* Corresponding author. Tel.: +380 44 5510669; fax: +380 44 573 26 43.
E-mail address: Lev@fluor.kiev.ua (L.M. Yagupolskii).
0022-1139/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2005.07.005

K.I. Petko et al. / Journal of Fluorine Chemistry 126 (2005) 1342–1346
1343
Scheme 2.
Scheme 1.
reaction products of compounds 2a–e with ethyl thiogly-
colate or 2-thiobenzothiazole, which contain less nucleo-
philic reaction centres compared to thiophenol and thiols,
were not obtained.
reactive, as its shielding from the counter ion decreases. We
found that the reaction of imidazolyl potassium with 1,2-
dibromotetrafluoroethane yields the N-(2-bromotetrafluoro-
ethyl) derivative in 76% yield. It is necessary to use freshly
sublimed potassium tert-butylate and thoroughly remove in
vacuum the residual tert-butanol from the imidazolyl
potassium obtained.
Compounds 3d and e, which do not contain easily
oxidizable heterocyclic rings were converted by heating
with hydrogen peroxide in acetic acid into the corresponding
sulfones 7d and e (Scheme 4).
We also investigated the reaction of compounds 2a–e
with sodium dithionite. The sodium salts of corresponding
sulfinic acids 8a–e were obtained in satisfactory yields
(Scheme 5).
Sodium salts of imidazole, benzimidazole, pyrazole, and
triazole, obtained with sodium hydride, react in the presence
of catalytic tetrabutylammonium iodide (TBAI), which
contains a bulky cation, with 1,2-dibromotetrafluoroethane
yielding 60–70% of the corresponding N-(2-bromotetra-
fluoroethyl) derivative. The reactions are carried out at room
temperature, or at 50–60 8C in the case of triazole. The most
active pyrrolyl sodium reacts in the absence of catalyst at
À10 8C with considerable warming and noticeable resini-
fication, unlike other heterocyclic derivatives. Tetrazolyl
sodium failed to react with 1,2-dibromotetrafluoroethane in
these conditions.
Salts 8a–e with reactive sulfinic group can be used as a
source for obtaining new sulfur-containing compounds
because alkylation and oxydation reactions of polyfluor-
oalkanesulfinates were well studied [18,19].
Thus, we found a useful way of 2-bromotetrafluoroethyl
group introduction at nitrogen atom of 5-membered
heterocycles. The ion-radical reactions with sulfur-con-
taining nucleofiles of compounds obtained were studied.
The products synthesized can be used for synthesis of new
fluorine-containing compounds.
We investigated the reactivity of bromine in the 2-
bromotetrafluoroethyl group. Ion-radical perfluoroalkyla-
tions of various sulfur-containing nucleophiles were con-
ducted by a procedure, described in ref. [17]. Compounds
2a–e reacted with thiophenol in liquid ammonia under UV
irradiation yielding the corresponding 2-heteroaryltetra-
fluoroethyl sulfides 3a–e (Scheme 2). The highest yield in
this reaction (86%) was obtained with triazole derivative 2e,
while for pyrrole derivative 2a side processes took place,
reducing the yield of 3a to 30%.
3. Experimental
3.1. General
1
Boiling and melting points are uncorrected. H NMR
spectra were recorded on a Varian VXR-300 instrument
(300 MHz, TMS as internal standard) and 19F NMR spectra
N-bromodifluoromethyl imidazole 4 [11,12] also reacts
by this route yielding the corresponding sulfide 5. 2-
Bromotetrafluoroethyl derivatives on nitrogen-containing
heterocycles can also react with aliphatic thiols. Thus,
compound 2b reacts with propylthiol-2 or 2-thioethanol
upon using these conditions. Corresponding sulfides 6a and
b were obtained in 48 and 43% yields (Scheme 3). The
were recorded on
a Gemini VXR-200 instrument
(188.5 MHz, CCl3F as internal standard). Sodium hydride
was used as 60% suspension in mineral oil (Aldrich) without
purification. DMF, previously distilled from BaO, was
freshly distilled from CaH2, immediately prior to use.
Commercially available starting heterocycles, thiols,
sodium dithionite and TBAI were used without purification.
Scheme 3.

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K.I. Petko et al. / Journal of Fluorine Chemistry 126 (2005) 1342–1346
3.2.3. N-(2-bromotetrafluoroethyl)benzimidazole (2c)
Yield 40%; bp 70–71 8C (0.2 Torr). 1H NMR (CDCl3): d
7.35–7.42 (m, 2H), 7.50–7.53 (m, 1H), 7.60–7.64 (m, 1H),
8.44 (s, 1H); 19F NMR (CDCl3): d À66.3 (s, 2F), À94.5 (s,
2F). Anal. Calcd. for C9H5BrF4N2: C, 36.4; H, 1.7; Br,
26.9%. Found: C, 36.4; H, 1.5; Br, 26.6%.
3.2.4. N-(2-bromotetrafluoroethyl)pyrazole (2d)
Yield 62%; bp 65–67 8C (70 Torr). 1H NMR (CDCl3): d
6.44 (s, 1H), 7.65 (s, 1H), 7.81 (s, 1H); 19F NMR (CDCl3); d
À65.2 (s, 2F), À95.9 (s, 2F). Anal. Calcd. for C5H3BrF4N2:
C, 24.35; H, 1.2; Br, 32.3%. Found: C, 24.2; H, 1.1; Br,
32.0%.
Scheme 4.
3.2.5. N-(2-bromotetrafluoroethyl)triazole-1,2,4 (2e)
Yield 63%; bp 51–53 8C (20 Torr). 1H NMR (CDCl3): d
8.06 (s, 1H), 8.28 (s, 1H); 19F NMR (CDCl3): d À67.0 (s,
2F), À96.9 (s, 2F). Anal. Calcd. for C4H2BrF4N3: C, 19.4; H,
0.8; Br, 32.2%. Found: C, 19.2; H, 0.7; Br, 32.1%.
Scheme 5.
3.3. General procedure for preparation of N-(2-pheny-
lthiotetrafluoroethyl)heterocycles (3a–e), N-phenyl-
thiodifluoromethylimidazole (5) and N-(2-alkylthi-
otetrafluoroethyl)imidazole (6a and b)
3.2. General procedure for preparation of
N-(2-bromotetrafluoroethyl)heterocycles (2a–e)
To a solution of thiol (0.01 mol) in liquid ammonia
(20 mL) in a Pyrex reactor, the compound 2a–e or 4
(0.01 mol) was added at À35 8C. After UV-irradiation with a
Hg lamp (PRK-4, 950 W) for 40 min, ammonia was
evaporated at room temperature. The residue was dissolved
in diethyl ether (50 mL), washed with 5% sodium carbo-
nate solution (50 mL), water (3 Â 50 mL), dried
over MgSO4, and, after removal of the solvent, the
product was distilled in vacuum or crystallized from hexane.
To a suspension of sodium hydride (0.021 mol) in
anhydrous DMF (10 mL) in an inert dry atmosphere, a
solution of the corresponding heterocycle 1a–e (0.02 mol) in
anhydrous DMF (10 mL) was added dropwise at 0 8C, or at
À10 8C in the case 1a. After stirring for 40 min,
tetrabutylammonium iodide (0.1 g) was added, (no catalyst
was used in the case of 1a), and, after stirring for 5 min, 1,2-
dibromotetrafluoroethane (10.5 g, 0.04 mol) was added in
one portion. After stirring for 2 h at 0 8C in the case 1a, at
25–35 8C in the case 1b–d, and at 50–55 8C in the case 1e,
the reaction mixture was poured into water (100 mL). The
oil formed was extracted with pentane (3 Â 50 mL) and
washed with water (3 Â 100 mL). The extract was dried
over MgSO4. After removal of the solvent, the product was
distilled in vacuum or at atmospheric pressure in the case of
2a.
3.3.1. N-(2-phenylthiotetrafluoroethyl)pyrrole (3a)
Yield 30%; bp 95–97 8C (0.5 Torr). 1H NMR (CDCl3): d
6.29–6.33 (m, 2H), 6.90–6.94 (m, 2H), 7.35–7.60 (m, 5H);
19F NMR (CDCl3): d À88.8 (s, 2F), À97.8 (s, 2F). Anal.
Calcd. for C12H9F4NS: C, 52.35; H, 3.3; S, 11.65%. Found:
C, 52.5; H, 2.9; S, 12.0%.
3.3.2. N-(2-phenylthiotetrafluoroethyl)imidazole (3b)
1
3.2.1. N-(2-bromotetrafluoroethyl)pyrrole (2a)
1
Yield 73%; mp 28–29 8C. H NMR (CDCl3): d 7.10 (s,
Yield 65%; bp 128–130 8C. H NMR (CDCl3): d 6.35–
1H), 7.32 (s, 1H), 7.35–7.65 (m, 5H), 7.96 (s, 1H); 19F NMR
(CDCl3): d À90.4 (s, 2F), À94.6 (s, 2F). Anal. Calcd. for
C11H8F4N2S: C, 47.8; H, 2.9; S, 11.6%. Found: C, 47.7; H,
2.7; S, 11.6%.
6.39 (m, 2H), 6.90–6.94 (m, 2H); 19F NMR (CDCl3): d
À67.4 (s, 2F), À95.2 (s, 2F). Anal. Calcd. for C6H4BrF4N:
C, 29.3; H, 1.6; Br, 32.5%. Found: C, 29.4; H, 1.3; Br,
32.1%.
3.2.2. N-(2-bromotetrafluoroethyl)imidazole (2b)
3.3.3. N-(2-phenylthiotetrafluoroethyl)benzim-
idazole (3c)
Yield 62%; mp 78–79 8C. 1H NMR (CDCl3): d 7.35–7.82
(m, 9H), 8.46 (s, 1H); 19F NMR (CDCl3): d À87.6 (s, 2F),
À93.1 (s, 2F). Anal. Calcd. for C15H10F4N2S: C, 55.2; H,
3.1; S, 9.8%. Found: C, 55.4; H, 3.0; S, 9.5%.
1
Yield 68%; mp 18–19 8C; bp 71–72 8C (20 Torr). H
NMR (CDCl3): d 7.29 (s, 1H), 7.52 (s, 1H), 8.10 (s, 1H); 19
F
NMR (CDCl3): d À68.3 (s, 2F), À94.0 (s, 2F). Anal. Calcd.
for C5H3BrF4N2: C, 24.3; H, 1.2; Br, 32.35%. Found: C,
24.4; H, 1.2; Br, 32.0%.

K.I. Petko et al. / Journal of Fluorine Chemistry 126 (2005) 1342–1346
1345
3.3.4. N-(2-phenylthiotetrafluoroethyl)pyrazole (3d)
3.4.2. N-(2-phenylsulfonyltetrafluoroethyl)triazole-1,2,4
(7e)
Yield 62%; bp 90–91 8C (0.5 Torr). 1H NMR (CDCl3): d
6.46 (s, 1H), 7.35–7.42 (m, 3H), 7.60–7.63 (m, 2H), 7.81–
7.96 (m, 2H); 19F NMR (CDCl3): d À88.2 (s, 2F), À95.7 (s,
2F). Anal. Calcd. for C11H8F4N2S: C, 47.8; H, 2.9; S, 11.6%.
Found: C, 47.7; H, 3.0; S, 11.7%.
1
Yield 72%; mp 104–105 8C. H NMR (CDCl3): d 7.81–
7.86 (m, 2H), 8.00–8.12 (m, 3H), 8.45 (s, 1H), 9.47 (s, 1H);
19F NMR (CDCl3): d À92.3 (s, 2F), À112.5 (s, 2F). Anal.
Calcd. for C10H7F4N3O2S: C, 38.8; H, 2.3; S, 10.4%. Found:
C, 38.7; H, 2.1; S, 10.3%.
3.3.5. N-(2-phenylthiotetrafluoroethyl)triazole-1,2,4
(3e)
Yield 86%; mp 72–73 8C. 1H NMR (CDCl3): d 7.35–7.61
(m, 5H), 8.10 (s, 1H), 8.48 (s, 1H); 19F NMR (CDCl3): d
À88.8 (s, 2F), À95.6 (s, 2F). Anal. Calcd. for C10H7F4N3S:
C, 43.3; H, 2.55; S, 11.6%. Found: C, 43.4; H, 2.5; S, 11.7%.
3.5. Sodium 2-(hetaryl-1-yl)tetrafluoroethanesulfinate
(8a–e)
To solutions of 2a–e (3 mmol) in oxygen-free acetonitrile
(7 mL) a solution of sodium dithionite (0.67 g, 85%,
3.3 mmol) and sodium hydrogen carbonate (0.28 g) in
oxygen-free water (5 mL) was added. After heating for 3 h at
60–65 8C, the solvent was evacuated and the solid residue
was extracted with iso-propanol (3 Â 10 mL). After
evaporation of the solvent, the sulfinate was washed with
benzene, and dried in vacuum.
3.3.6. N-(phenylthiodifluoromethyl)imidazole (5)
Yield 66%; bp 95–97 8C (0.5 Torr). 1H NMR (CDCl3): d
7.00 (s, 1H), 7.12 (s, 1H), 7.35–7.65 (m, 5H), 7.86 (s, 1H);
19F NMR (CDCl3): d À54.8 (s, 2F). Anal. Calcd. for
C10H8F2N2S: C, 53.1; H, 3.6; S, 14.2%. Found: C, 52.8; H,
3.0; S, 14.2%.
3.5.1. Sodium 2-(pyryl-1-yl)tetrafluoroethanesulfinate
(8a)
1
3.3.7. N-(2-isopropylthiotetrafluoroethyl)imidazole (6a)
Yield 48%; bp 104–105 8C (20 Torr). 1H NMR (CDCl3):
Yield 51%; mp 150 8C (dec). H NMR (DMSO-d6): d
6.24 (m, 2H), 7.04 (m, 2H); 19F NMR (DMSO-d6): d À89.5
(s, 2F), À129.2 (s, 2F). Anal. Calcd. for C6H4F4NNaO2S: C,
28.5; H, 1.6; N, 5.5%. Found: C, 28.1; H, 1.6; N, 5.4%.
3
3
d 1.37 (d, 6H JH–H = 5.0 Hz), 3.47 (sept, 1H JH–
H = 5.0 Hz), 7.02 (s, 1H), 7.13 (s, 1H), 7.77 (s, 1H); 19F
NMR (CDCl3): d À89.2 (s, 2F), À95.1 (s, 2F). Anal. Calcd.
for C8H10F4N2S: C, 39.7; H, 4.2; S, 13.2%. Found: C, 40.0;
H, 4.3; S, 13.5%.
3.5.2. Sodium 2-(imidazolyl-1-yl)tetrafluoroethanesul-
finate (8b)
1
Yield 46%; mp 193 8C (dec). H NMR (DMSO-d6): d
7.10 (s, 1H), 7.49 (s, 1H), 8.08 (s, 1H); 19F NMR (DMSO-
d6): d À89.0 (s, 2F), À129.3 (s, 2F). Anal. Calcd. for
C5H3F4N2NaO2S: C, 23.6; H, 1.2; N, 11.0%. Found: C, 23.3;
H, 1.4; N, 10.8%.
3.3.8. N-[2-(2-hydroxyethylthio)-tetrafluoroethyl]imi-
dazole (6b)
Yield after column chromatography (with CHCl3 as an
1
eluent) 43%; mp 22–23 8C; bp 120–122 8C (0.2 Torr). H
NMR (CDCl3): d 3.01 (t, 2H JH–H = 5.9 Hz), 3.81 (t, 2H
3
3JH–H = 5.9 Hz), 7.12 (s, 1H), 7.16 (s, 1H), 7.79 (s, 1H); 19
F
3.5.3. Sodium 2-(benzimidazolyl-1-yl)tetrafluoroethane-
sulfinate (8c)
NMR (CDCl3): d À90.0 (s, 2F), À95.1 (s, 2F). Anal. Calcd.
for C7H8F4N2OS: C, 34.4; H, 3.3; S, 13.1%. Found: C, 34.8;
H, 3.6; S, 13.3%.
1
Yield 59%; mp 251 8C (dec). H NMR (DMSO-d6): d
7.37–7.41 (m, 2H); 7.60 (d, 1H); 7.74 (d, 1H); 8.48 (s, 1H);
19F NMR (DMSO-d6): d À90.5 (s, 2F), À127.6 (s, 2F). Anal.
Calcd. for C9H5F4N2NaO2S: C, 35.5; H, 1.7; N, 9.2%.
Found: C, 35.3; H, 1.9; N, 9.5%.
3.4. N-(2-phenylsulfonyltetrafluoroethyl)heterocycles
(7d and e)
To solutions of sulfides 3d and e (5 mmol) in acetic acid
(10 mL), 40% aqueous H2O2 (10 mL), was added. After
refluxing for 3 h, water (30 mL) was added to the reaction
mixture. The precipitate, formed after cooling, was filtered
off, dried and crystallized from hexane.
3.5.4. Sodium 2-(pyrazolyl-1-yl)tetrafluoroethane-
sulfinate (8d)
Yield 67%; mp 164 8C. 1H NMR (DMSO-d6): d 6.51 (s,
1H), 7.78 (s, 1H), 8.17 (s, 1H); 19F NMR (DMSO-d6): d
À94.4 (s, 2F), À131.3 (s, 2F). Anal. Calcd. for
C5H3F4N2NaO2S: C, 23.6; H, 1.2; N, 11.0%. Found: C,
23.4; H, 1.2; N, 10.9%.
3.4.1. N-(2-phenylsulfonyltetrafluoroethyl)pyrazole (7d)
1
Yield 64%; mp 72–74 8C. H NMR (CDCl3): d 6.48 (s,
1H), 7.60–7.65 (m, 2H), 7.75–7.85 (m, 3H), 7.97 (s, 1H),
8.00 (s, 1H); 19F NMR (CDCl3): d À93.4 (s, 2F), À112.8 (s,
2F). Anal. Calcd. for C11H8F4N2O2S: C, 42.65; H, 2,6; S,
10.4%. Found: C, 42.6; H, 2.7; S, 10.2%.
3.5.5. Sodium 2-(triazolyl-1-yl)tetrafluoroethane-
sulfinate (8e)
1
Yield 61%; mp 202 8C (dec). H NMR (DMSO-d6): d
8.30 (s, 1H), 9.11 (s, 1H); 19F NMR (DMSO-d6): d À94.4 (s,

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[9] V.V. Rudyuk, D.V. Fedyuk, L.M. Yagupolskii, J. Fluorine Chem. 125
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2F), À131.3 (s, 2F). Anal. Calcd. for C4H2F4N3NaO2S: C,
18.8; H, 0.8; N, 16.5%. Found: C, 19.3; H, 1.0; N, 16.9%.
[10] L.M. Yagupolskii, D.V. Fedyuk, Tetrahedron Lett. 41 (2000) 2265–
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