N-(2-chloro-1,2-difluorovinyl) derivatives of azoles

Article abstract of DOI:10.1134/S1070428010040172

Reactions of N-(2,2-dichloro-1,1,2-trifluoroethyl)-substituted azoles with zinc, magnesium, butyllithium, and tris(diethylamino)phosphine were studied, and optimal conditions for the preparation of the corresponding N-(2-chloro-1,2-difluorovinyl) derivati

Full text of DOI:10.1134/S1070428010040172

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 4, pp. 546–550. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © K.I. Petko, S.Yu. Kot, L.M. Yagupol’skii, 2010, published in Zhurnal Organicheskoi Khimii, 2010, Vol. 46, No. 4, pp. 555–559.
N-(2-Chloro-1,2-difluorovinyl) Derivatives of Azoles
K. I. Petko, S. Yu. Kot, and L. M. Yagupol’skii†
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, ul. Murmanskaya 5, Kiev, 02660 Ukraine
e-mail: kirpet@ukr.net
Received February 17, 2009
Abstract—Reactions of N-(2,2-dichloro-1,1,2-trifluoroethyl)-substituted azoles with zinc, magnesium, butyl-
lithium, and tris(diethylamino)phosphine were studied, and optimal conditions for the preparation of the cor-
responding N-(2-chloro-1,2-difluorovinyl) derivatives were found [tris(diethylamino)phosphine, chlorotri-
methylsilane]. Some reactions of the obtained unsaturated fluorinated compounds with sulfur-centered nucleo-
philes were examined.
DOI: 10.1134/S1070428010040172
Nitrogen-containing heterocycles are used as build-
ing blocks in the synthesis of biologically active com-
pounds. Many drugs and pesticides are derivatives of
imidazole, pyrazole, and indole. Introduction of
a fluorine atom or fluorine-containing substituent into
molecules of biologically active compounds often en-
hances their stability and reduces toxicity; in this case,
the original biological activity is generally retained or
sometimes improved. Most fluorine-containing azoles
synthesized previously contain fluorinated groups at
endocyclic carbon atoms, whereas azoles with fluori-
nated groups on the nitrogen have been studied poorly.
yields of the final products were as poor as 5–25%.
Only the reaction with 3,5-dimethyl-1H-pyrazole gave
54% of 1-(2-chloro-1,2-difluorovinyl)-3,5-dimethyl-
1H-pyrazole.
The goal of the present work was to develop a pre-
parative procedure for the synthesis of N-(2-chloro-
1,2-difluorovinyl)-substituted azoles and examine their
chemical properties. As starting compounds we used
N-(2,2-dichloro-1,2,2-trifluoroethyl)azoles Ia–Ie
which were synthesized previously. Azoles Ia–Ie were
subjected to elimination of fluorine and chlorine atoms
in the vicinal positions of the dichlorotrifluoroethyl
fragment.
We previously examined reactions of azoles with
various polyhaloperfluoroethanes possessing chlorine,
bromine, and iodine together with fluorine atoms, e.g.,
Freons 113 (CFCl2CF2Cl) and 114–B2 (CF2BrCF2Br)
and 2-chloro-1,1,2,2-tetrafluoro-1-iodoethane] [1–3],
and obtained N-(2,2-dichloro-1,2,2-trifluoroethyl) [1],
N-(2-bromo-1,1,2,2-tetrafluoroethyl) [2], and
N-(1,1,2,2-tetrafluoro-2-iodoethyl) [3] derivatives of
the corresponding heterocycles. Perfluoroalkenes
exhibit high reactivity toward different nucleophiles,
and such reactions are widely used in the synthesis of
various fluorinated compounds. Introduction of unsatu-
rated fluorine-containing moieties into heterocyclic
compounds could give rise to new highly reactive
synthons.
Elimination of two chlorine atoms from Freon 113
molecule with formation of chlorotrifluoroethylene is
usually accomplished by the action of metallic zinc in
alcoholic medium [5]. We tried to perform analogous
transformation of compound Id using zinc dust. How-
ever, instead of elimination of chlorine and fluorine
atoms, one chlorine atom in the dichlorotrifluoroethyl
fragment was replaced by hydrogen to give
1-(2-chloro-1,2,2-trifluoroethyl)-3,5-dimethyl-1H-pyr-
azole (IId) (Scheme 1). Presumably, intermediate
organozinc compounds was hydrolyzed with protic
solvent. No reaction occurred with zinc dust in aprotic
solvent (DMF) even on prolonged heating.
Compound Ic failed to react with more active
magnesium in anhydrous diethyl ether despite addi-
tional activation with iodine, metallic sodium, sodium
hydride, or metallic potassium. The surface of magne-
sium particles was coated with halides that are in-
soluble in diethyl ether and was thus deactivated. We
N-(2-Chloro-1,2-difluorovinyl)-substituted azoles
were synthesized for the first time in our laboratory by
reaction of the corresponding azole sodium salts with
1,2-dichloro-1,2-difluoroethene [4]. However, the
†
Deceased.
546

N-(2-CHLORO-1,2-DIFLUOROVINYL) DERIVATIVES OF AZOLES
547
Scheme 1.
F
Cl
(Et3N)3P
Ht
Ht
HtCF2CFCl2
+
Cl
F
–(Et3N)3PCl2
–(Et3N)3PF2
F
F
Ia–Ie
IIIa–IIIe
F
F
Cl
Cl
Mg, THF or BuLi
30 or 54%
Cl
+
F
N
N
N
Cl
N
N
N
F
F
F
F
Ic
IIIc
F
F
F
Cl
H
Me
Me
Zn, EtOH
64%
N
N
N
Cl
Cl
N
F
F
F
Me
Me
Id
IId
Ht = 1H-imidazol-1-yl (a), 1H-benzimidazol-1-yl (b), 1H-pyrazol-1-yl (c), 3,5-dimethyl-1H-pyrazol-1-yl (d), 1H-indol-1-yl (e).
succeeded in obtaining N-(2-chloro-1,2-difluorovinyl)-
pyrazole (IIIc) in 30% yield in the reaction with mag-
nesium in tetrahydrofuran at 50°C, though the process
was accompanied by strong tarring. The ratio of the
trans and cis isomers of IIIc was 1:1. A drawback of
this procedure is that compound IIIc itself is capable
of reacting with metallic magnesium. If an equimolar
amount of magnesium is used, the reaction mixture
always contains unchanged initial compound, and
excess magnesium is necessary to ensure its complete
conversion.
We also succeeded in obtaining compound IIIc
using butyllithium as dehalogenating agent. The yield
of IIIc was 54%, and the cis/trans isomer ratio was
3:1. However, analogous reactions of some other het-
erocycles, e.g., imidazole, were accompanied by con-
current lithiation of the heteroring, so that the yield of
the target product decreased to 10%.
reaction with metals, for the reagent did not react with
the products. The reactions were carried out in anhy-
drous aprotic solvents. In the presence of even traces
of water 2-chloro-1,1,2-trifluoroethyl derivatives like
II are formed as by-products. The reaction rate
depends on the basicity of the initial heterocycle. For
example, benzimidazole derivative Ib reacts in hexane
at room temperature in 12 h, whereas dehalogenation
of indole derivative Ie required heating under reflux
over a period of 12 h. In all cases, the target products
contained some amounts of unreacted tris(diethyl-
amino)phosphine and the other product, tris(diethyl-
amino)difluorophosphorane, as impurities. Low-boil-
ing imidazole, pyrazole, and 3,5-dimethylpyrazole
derivatives IIIa, IIIc, and IIId can be isolated by
fractional distillation. In the case of benzo-fused het-
erocycles, benzimidazole and indole derivatives IIIb
and IIIe, the boiling points of the target products and
by-products were fairly similar. 1-(2-Chloro-1,2-di-
fluorovinyl)-1H-indole (IIIe) was readily purified
from by-products by chromatography using hexane as
eluent (Rf ≈ 0.5) and was isolated in 78% yield. How-
ever, we failed to purify compound IIIb in such a way.
Koidan et al. [6] previously described elimination
of fluorine and chlorine atoms from 1,1,1-trichloro-
2,2,2-trifluoroethane with simultaneous phosphoryla-
tion by the action of tris(diethylamino)phosphine. The
use of tris(diethylamino)phosphine as dehalogenating
agent toward N-(2,2-dichloro-1,1,2-trifluoroethyl)-
azoles gave considerably better results than in the
With a view to facilitate isolation of the dehalo-
genation products we used excess tris(diethylamino)-
Scheme 2.
F
Cl
110–120°C
–Me3SiF
Ht
Ht
HtCF2CFCl2
+
(Et3N)3P + Me3SiCl
[HtCF2CFClSiMe3]
+
Cl
F
–(Et3N)3PCl2
F
F
Ia–Ie
IVa–IVe
IIIa–IIIe
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010

PETKO et al.
548
Scheme 3.
F
F
F
Br2, hexane–H2O
NaHCO3
4-ClC6H4SNa
THF
Me
Br
Me
Me
Cl
Cl
S
N
N
N
N
N
N
C6H4Cl-4
F
F
F
Me
Me
Me
V
IIId
VI
Scheme 4.
F
F
4-ClC6H4S
4-ClC6H4SNa
THF
Cl
S
SC6H4Cl-4
N
N
N
N
+
C6H4Cl-4
N
N
F
F
SC6H4Cl-4
VIII
IIIc
VII
phosphine and excess chlorotrimethylsilane, which
allowed us to avoid formation of tris(diethylamino)-
difluorophosphorane (Scheme 2). In this case,
N-(2-chloro-1,1,2-trifluoro-2-trimethylsilylethyl)azoles
IVa–IVe were formed as intermediate products; their
19F NMR spectra were consistent with the data report-
ed by us previously [7]. In the presence of chlorotri-
methylsilane tris(diethylamino)phosphine reacted with
compounds Ia–Ie at the terminal chlorine atom to give
dichlorotris(diethylamino)phosphorane which, unlike
tris(diethylamino)difluorophosphorane, is a nonvolatile
compound. After removal of the solvent, the residue
was slowly heated on an oil bath to 110–120°C with
simultaneous evacuation. Under these conditions,
intermediate silanes IVa–IVe decomposed with forma-
tion of unsaturated fluorinated compounds IIIa–IIIe.
This procedure made it possible to obtain target com-
pounds IIIa–IIId in 60–80% yield. The yield of IIIe
was lower (29%). In all cases, the cis–trans isomer
ratio was approximately 1:1.
lution of bromine in hexane to give 4-bromo derivative
V, while the fluorinated double bond remained unaf-
fected (Scheme 3). The reaction of the same substrate
with sodium 4-chlorobenzenethiolate readily occurred
at room temperature. Nucleophilic replacement may
involve both one chlorine atom and all three halogen
atoms in the unsaturated trihalovinyl moiety. In the
reaction of compound IIId with an equimolar amount
of sodium 4-chlorobenzenethiolate we isolated 60% of
product VI formed as a result of replacement of one
chlorine atom (Scheme 3). The product ratio also
depended on steric hindrances. Analogous reaction of
IIIc (equimolar amounts of the reactants) afforded
~35% of chlorine replacement product VII and ~35%
of compound VIII (exhaustive replacement of halogen
atoms; Scheme 4). The monosubstitution products
were characterized exclusively by trans arrangement
of the fluorine atoms, as followed from the corre-
sponding 19F–19F coupling constant.
To conclude, we have developed a preparative
procedure for the synthesis of difficultly accessible
compounds having an unsaturated fluorinated frag-
ment, N-(2-chloro-1,2-difluorovinyl)azoles, and
studied some their chemical properties.
Compounds IIIa–IIIe are mobile volatile liquids.
Signals from cis-fluorine atoms in their 19F NMR spec-
tra appeared as doublets of doublets with a coupling
constant of ~25 Hz, while trans-oriented fluorine
atoms gave rise rise to doublets of doublets with
a coupling constant of ~125–130 Hz. Depending on
the solvent, fluorine nuclei can also resonate as sin-
glets. For instance, compound IIIc in CDCl3 displayed
a narrow singlet from the cis-fluorine atoms in the
19F NMR spectrum, while the corresponding signals in
the spectra recorded in other solvents (e.g., in dimethyl
sulfoxide) were split.
EXPERIMENTAL
1
The H and 19F NMR spectra were recorded on
1
a Varian VXR-300 instrument (300 MHz for H); the
chemical shifts were determined relative to tetra-
methylsilane (1H) or trichlorofluoromethane (19F) as
internal reference. Tetrahydrofuran and diethyl ether
were purified by distillation over metallic sodium in
the presence of benzophenone as indicator. Methylene
chloride was purified by distillation over phosphoric
anhydride.
We examined some chemical properties of unsatu-
rated compounds IIIa–IIIe. The exocyclic double C=C
bond in their molecules turned out to be stable to
elemental bromine. Compound IIId reacted with a so-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010

N-(2-CHLORO-1,2-DIFLUOROVINYL) DERIVATIVES OF AZOLES
549
1-(2-Chloro-1,1,2-trifluoroethyl)-3,5-dimethyl-
1H-pyrazole (IId). Zinc dust, 0.4 g (6 mmol), was
added to a solution of 1 g (4 mmol) of compound Id in
10 ml of ethanol. The mixture was stirred for 4 h on
heating under reflux. Unreacted zinc was filtered off
and washed with alcohol, the filtrate was combined
with the washings and evaporated almost to dryness.
A mixture of 15 ml of hexane and 5 ml of 5% hydro-
chloric acid was added to the residue, the aqueous
phase was separated, the organic phase was washed
with water (3×20 ml), dried over MgSO4, and evap-
orated, and the residue was distilled under reduced
pressure. Yield 0.54 g (64%), bp. 70–72°C (20 mm).
1H NMR spectrum (CDCl3), δ, ppm: 2.27 s (3H, CH3),
2.42 s (3H, CH3), 5.66 s (1H, 4-H), 6.25 d.t (1H,
was added to a solution of 10 mmol of compound Іa–
Id in 15 ml of anhydrous methylene chloride, and
a solution of 2.48 g (10 mmol) of tris(diethylamino)-
phosphine in 10 ml of anhydrous methylene chloride
was added dropwise under vigorous stirring over
a period of 30 min (the temperature of the reaction
mixture should not exceed 25°C). The mixture was
stirred for 40 min and evaporated under reduced pres-
sure. The residue was slowly added to 110–120°C on
an oil bath with simultaneous isolation of the target
products by vacuum distillation. cis/trans Isomer
ratio ~1:1.
1-(2-Chloro-1,2-difluorovinyl)-1H-imidazole
(IIIa). Yield 0.87 g (54%), bp 65–66°C (20 mm);
published data [4]: bp 58°C (10 mm).
2
3
CHFCl, J = 56, J = 4 Hz). 19F NMR spectrum
(CDCl3), δF, ppm: –148.55 d.m (1F, CFClH), –95.45
(2F, AB system, NCF2, J ≈ 180 Hz). Found, %:
C 39.67; H 3.27; Cl 16.72. C7H8ClF3N2. Calculated,
%: C 39.55; H 3.39; Cl 16.68.
1-(2-Chloro-1,2-difluorovinyl)-1H-benzimidazole
(IIIb). Yield 1.68 g (78%), bp 72–74°C (0.2 mm).
1H NMR spectrum (CDCl3), δ, ppm: 7.36–7.39 m (2H,
5-H, 6-H), 7.71–7.76 m (1H, 4-H), 7.82–7.88 m (1H,
19
7-H), 8.13 s (1H, 2-H). F NMR spectrum (CDCl3),
1-(2-Chloro-1,2-difluorovinyl)-1H-pyrazole
(IIIc). a. A solution of 1 g (4.5 mmol) of compound Ic
in 10 ml of anhydrous tetrahydrofuran was added to
0.17 g (7 mmol) of activated magnesium. The mixture
was stirred for 2 h at 50°C, the solvent was distilled off
under reduced pressure, and the product was extracted
into methylene chloride (3×20 ml). The extract was
evaporated, and the residue was distilled under reduced
pressure. Yield 0.24 g (30%), bp 51–53°C (35 mm).
1H NMR spectrum (CDCl3), δ, ppm: 6.41–6.43 m (1H,
4-H), 7.71–7.73 m (1H, 5-H), 7.84–7.86 m (1H, 3-H).
19F NMR spectrum, δF, ppm: in CDCl3: –125.55 d (1F,
trans-F, J = 130 Hz), –120.95 d (1F, trans-F, J =
130 Hz), –106.83 s (2F, cis-F); in DMSO-d6: –124.48 d
(1F, trans-F, J = 130 Hz), –121.74 d (1F, trans-F, J =
130 Hz), –108.97 d (1F, cis-F, J = 29 Hz), –106.95 d
(1F, cis-F, J = 29 Hz). cis/trans Isomer ratio 1:1.
Found, %: C 36.37; H 1.77; Cl 21.72. C5H3ClF2N2.
Calculated, %: C 36.50; H 1.84; Cl 21.55.
δF, ppm: –124.48 d (trans-F, J = 128 Hz), –118.72 d
(trans-F, J = 128 Hz), –108.87 d (1F, cis-F, J = 27 Hz),
–104.84 d (1F, cis-F, J = 27 Hz). Found, %: C 50.46;
H 2.47; Cl 16.32. C9H5ClF2N2. Calculated, %:
C 50.37; H 2.35; Cl 16.52.
1-(2-Chloro-1,2-difluorovinyl)-1H-pyrazole
(IIIc). Yield 1.21 g (74%).
1-(2-Chloro-1,2-difluorovinyl)-3,5-dimethyl-1H-
pyrazole (IIId). Yield 1.47 g (77%), bp 68–70°C
(20 mm); published data [4]: bp 61°C (10 mm).
1-(2-Chloro-1,2-difluorovinyl)-1H-indole (IIIe).
A solution of 5.38 g (20 mol) of compound Ie in 20 ml
of anhydrous tetrahydrofuran was mixed with a solu-
tion of 5.2 g (21 mmol) of tris(diethylamino)phosphine
in 20 ml of anhydrous tetrahydrofuran, and the mixture
was stirred for 12 h at room temperature. The solvent
was evaporated, the residue was treated with 10 ml of
hexane, and the hexane solution was subjected to
chromatography on silica gel, the first fraction being
collected. The eluate was evaporated, and the residue
was distilled under reduced pressure. Yield 3.34 g
b. A solution of 1.75 g (8 mmol) of compound Ic in
30 ml of anhydrous diethyl ether was cooled to –20°C,
6.4 ml (16 mmol) of a 2.5 M solution of butyllithium
in hexane was added dropwise over a period of 1 h,
and the mixture was stirred for 1 h at that temperature
and allowed to slowly warm up to room temperature.
The solvent was evaporated, and the residue was
distilled under reduced pressure. Yield 0.71 g (54%);
cis/trans isomer ratio 1:3.
1
(78%), bp 110–112°C (20 mm). H NMR spectrum
(CDCl3), δ, ppm: 6.73–6.75 m (1H, 3-H), 7.12–7.16 m
(1H, 4-H), 7.21–7.45 m (3H, 2-H, 5-H, 6-H), 7.65–
7.66 m (1H, 7-H). 19F NMR spectrum, δF, ppm: in
CDCl3: –121.17 s (2F, trans-F), –108.97 d (1F, cis-F,
J = 25 Hz), –103.67 d (1F, cis-F, J = 25 Hz); in
DMSO-d6: –121.74 (2F, AB system, trans-F, J ≈
125 Hz), –107.97 d (1F, cis-CF, J = 25 Hz), –104.35 d
N-(2-Chloro-1,2-difluorovinyl)azoles IIIa–IIId
(general procedure). Chlorotrimethylsilane, 2.5 ml,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010

PETKO et al.
550
(1F, cis-CF, J = 25 Hz). cis/trans Isomer ratio 1 :1.
Found, %: C 56.27; H 2.71; Cl 16.87. C10H6ClF2N2.
Calculated, %: C 56.23; H 2.83; Cl 16.60.
Cl 11.91; S 10.40. C13H11ClF2N2S. Calculated, %:
Cl 11.79; S 10.66.
1-[(Z)-2-(4-Chlorophenylsulfanyl)-1,2-difluoro-
vinyl]-1H-pyrazole (VII). Yield 0.43 g (35%), bp 88–
4-Bromo-1-(2-chloro-1,2-difluorovinyl)-3,5-di-
methyl-1H-pyrazole (V). A solution of 0.96 g
(5 mmol) of compound IIId in 10 ml of hexane was
mixed with a solution of 1 g of sodium hydrogen
carbonate in 15 ml of water, and a solution of 0.8 g
(5 mmol) of bromine in 5 ml of hexane was added
dropwise under vigorous stirring at room temperature.
The solution quickly turned colorless. The hexane
layer was separated and washed with a 1% solution of
sodium sulfite (10 ml) and water (3×50 ml). The sol-
vent was distilled off, and the residue was distilled
under reduced pressure. Yield 1.13 g (84%), bp 87–
1
90°C (0.5 mm), Rf 0.7. H NMR spectrum (CDCl3), δ,
ppm: 6.61–6.63 m (1H, 4-H), 7.55 (4H, AB system,
H
arom), 7.91–7.93 m (1H, 3-H), 8.28 s (1H, 5-H).
19F NMR spectrum (CDCl3), δF, ppm: –132.53 d (1F,
J = 142 Hz), –115.45 d (1F, J = 142 Hz). Found, %:
Cl 12.91; S 11.64. C11H7ClF2N2S. Calculated, %:
Cl 13.00; S 11.76.
1-[1,2,2-Tris(4-chlorophenylsulfanyl)vinyl]-1H-
pyrazole (VIII). Yield 0.25 g (15%), mp 105–107°C,
1
Rf 0.25. H NMR spectrum (CDCl3), δ, ppm: 6.26–
6.27 m (1H, 4-H), 7.11 d (2H, Harom), 7.25 d (2H,
1
88°C (15 mm). H NMR spectrum (CDCl3), δ, ppm:
Harom), 7.31 (4H, AB system, Harom), 7.37 d (2H, Harom),
2.25 s (3H, CH3), 2.36 s (3H, CH3). 19F NMR spectrum
(CDCl3), δF, ppm: –129.78 d (trans-F, J = 129 Hz),
–116.36 d (trans-F, J = 129 Hz), –108.87 d (1F, cis-F,
J = 23 Hz), –104.69 d (1F, cis-F, J = 23 Hz). cis/trans
Isomer ratio 1 : 1. Found, %: C 31.10; H 2.40;
Br 28.97. C7H6BrClF2N2. Calculated, %: C 30.97;
H 2.23; Br 29.43.
7.44 d (2H, Harom), 7.52–7.53 m (1H, 3-H), 7.91–
7.93 m (1H, 5-H). Found, %: Cl 20.11; S 18.05.
C23H15Cl3N2S3. Calculated, %: Cl 20.38; S 18.43.
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sodium 4-chlorobenzenethiolate. A solution of
5 mmol of compound ІІІc or IIId in 5 ml of anhydrous
tetrahydrofuran was mixed at room temperature with
0.83 g (5 mmol) of sodium 4-chlorobenzenethiolate,
and the mixture was left to stand for 12 h. The solvent
was distilled off, and the residue was subjected to
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chloroform–hexane (3:1) as eluent.
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1-[(Z)-2-(4-Chlorophenylsulfanyl)-1,2-difluoro-
vinyl]-3,5-dimethyl-1H-pyrazole (VI). Yield 0.9 g
1
(60%), bp 93–95°C (0.2 mm), Rf 0.65. H NMR spec-
trum (CDCl3), δ, ppm: 2.21 s (3H, CH3), 2.25 s (3H,
CH3), 5.91 s (1H, 4-H), 7.45 (4H, AB system, Harom).
19F NMR spectrum (CDCl3), δF, ppm: –128.33 d (1F,
J = 142 Hz), –110.55 d (1F, J = 142 Hz). Found, %:
7. Petko, K.I., Kot, S.Y., and Yagupolskii, L.M., J. Fluorine
Chem., 2008, vol. 129, p. 301.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010