Synthesis and properties of 1-trifluoroacetylacetylene

Full text of DOI:10.1134/S0012500806060012

ISSN 0012-5008, Doklady Chemistry, 2006, Vol. 408, Part 2, pp. 87–89. © Pleiades Publishing, Inc., 2006.
Original Russian Text © N.P. Tsvetkov, A.B. Koldobskii, I.V. Korznikova, A.S. Peregudov, V.N. Kalinin, 2006, published in Doklady Akademii Nauk, 2006, Vol. 408, No. 4,
pp. 481–482.
CHEMISTRY
Synthesis and Properties of 1-Trifluoroacetylacetylene
N. P. Tsvetkov, A. B. Koldobskii, I. V. Korznikova, A. S. Peregudov, and V. N. Kalinin
Presented by Academician Yu.N. Bubnov November 17, 2005
Received November 25, 2005
DOI: 10.1134/S0012500806060012
The Diels–Alder reaction is one of the most general lene 2 in high yield; the second reaction product, tri-
methods for the synthesis of different six-membered methylstannyl trifluoroacetate, is precipitated. The use
heterocyclic compounds containing functional groups of high-boiling ethyl benzoate as a solvent makes it
[
1–3]. The presence of the trifluoroacetyl group in a
possible to isolate the target compound by distillation
from the reaction mixture.
dienophile should result in its considerable activation in
cycloaddition reactions and open a simple way to the
synthesis of complex fluorine-containing compounds
showing biological activity [4, 5].
Me Sn–C≡C–COCF + CF CO H
3
3
3
2
1
In recent years, our research group has developed
methods of preparing halogen-substituted trifluoro-
acetylacetylenes and studied their reactions with differ-
ent dienes and alkenes [6–9]. There is a sole report in
the literature on the synthesis of 1-trifluoroacetylacety-
lene, the parent compound of this series; however, the
compound was obtained only in trace amounts in a low
yield after separation of an isomer mixture using a liq-
uid chromatograph [10].
H–C≡C–COCF + CF CO SnMe
3 3 2 3
2, 85%
Acetylene 2 is a low-boiling compound (bp 31°C)
stable upon storage in the absence of moisture and
showing high reactivity in the Diels–Alder reaction
with different dienes. Thus, the addition reaction to
cyclopentadiene is completed in several minutes at 0°C,
whereas the reaction with less reactive cyclohexadiene
and 2,3-dimethylbutadiene requires several hours at
In the present paper, we describe a preparative
method for the synthesis of trifluoroacetylacetylene and
report the results of studying its properties.As a starting
compound, we used 1-trimethylstannyl-2-trifluoro-
acetylacetylene 1, readily obtainable from bis(trimeth-
ylstannyl)acetylene and trifluoroacetic anhydride [8].
2
0°C.
COCF3
3
a
Me Sn–C≡C–SnMe + (CF CO) O
3
3
3
2
0°C/15 min
Me Sn–C≡C–COCF + CF CO SnMe
3
3
3
3
2
1
, 90%
COCF3
H–C≡C–COCF3
2
0°C/12 h
The trimethylstannyl substituent in compound 1 is
known to undergo electrophilic substitution by a halo-
gen atom under mild conditions [8]. Taking into
account this feature, we supposed that the electrophilic
substitution of a proton for this residue could proceed
similarly.
2
3b
2
0°C/20 h
COCF3
Indeed, the treatment of acetylene 1 with trifluoro-
acetic acid was found to result in trifluoroacetylacety-
3
c
Although cycloadducts 3a, 3b, and 3c can be dis-
tilled in a vacuum, we revealed an unusual dimerization
reaction for bicyclic compounds 3a and 3b, which is
completed in the case of cycloadduct 3a at 20°ë in the
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28, Moscow,
119991 Russia
8
7

8
8
TSVETKOV et al.
absence of a solvent over 48 h, while cycloadduct 3b mixture was vigorously stirred under a vacuum of 10–
undergoes complete dimerization during six weeks.
15 mmHg until the distillation of the product within
5–65°C ceased (the distillation residue accumulating
4
Therefore, the latter compound can be purified by
vacuum distillation, but bicyclic compound 3a should
be used immediately after the cycloaddition reaction is
completed because the distillation is accompanied by
fast dimerization.
trimethylstannyl trifluoroacetate quickly solidified and
partially sublimed, and the stirring was hampered, but
the distillation should not be stopped). An additional
portion of the product was distilled off from the reac-
tion mixture in a vacuum of an oil pump at 1–2 mmHg
after the receiver was replaced. The product was redis-
tilled to give 72.7 g (90%) of acetylene 1, bp 53–56°C/8
mmHg.
Cycloadducts 3a and 3b were shown to undergo
dimerization via the Diels–Alder reaction where the
conjugated C=C bond of one molecule behaves as the
dienophile component, while the conjugated C=C–
C=O system of the other reacts as the diene component.
1-Trifluoroacetylacetylene 2. A solution of 6.0 g
3.9 mL, 0.052 mol) of trifluoroacetic acid in 5 mL of
(
ethyl benzoate was added dropwise to a solution of 15 g
(0.052 mol) of acetylene 1 in 10 mL of ethyl benzoate
with stirring and cooling to –20°C. The solution was
stirred for 15 min at 20°C, then the mixture was gradu-
ally heated to distill the product off through a short dis-
tilling column into a trap with a receiver cooled with
dry ice. The product was redistilled to give 5.4 g (85%)
of acetylene 2, bp 31°C.
H
2
0°C/48 h
COCF3
H
O
CF3
COOF3
3
a
4a
H
H
General procedure for the synthesis of cycload-
ducts 3. An appropriate diene (0.0052 mol) was added
to a solution of 0.64 g (0.0052 mol) of acetylene 2 in
2.5 mL of anhydrous diethyl ether (deuteriochloroform
2
0°C/42 days
COCF3
COOF3
O
1
CF3
was used as the solvent when H NMR monitoring of
3
b
4b
the reaction course was necessary). When cyclopenta-
diene was used, the reagents were mixed at –15°C and
kept for 1 h at 0°C to bring about the quantitative for-
Dimers 4a and 4b are stable crystalline solids. At
present, we are studying the reasons for such easy
dimerization of cycloadducts 3a and 3b, as well as the
mutual spatial arrangement of bicycles in 4a and 4b
molecules.
1
mation of cycloadduct 3a as shown by H NMR data.
For the reaction of cyclohexadiene and 2,3-dimethylb-
utadiene, the reaction mixture was kept for the required
time at a prescribed temperature and then distilled in a
vacuum to give 0.76 g (72%) of adduct 3b, bp 90–92°C
(
20 mmHg), and 0.9 g (84%) of adduct 3c, bp 80–90°C
EXPERIMENTAL
(15 mmHg).
All manipulations with trimethylstannyltrifluoro-
acetylacetylene were performed in an argon atmo-
sphere with the use of anhydrous solvents. Trifluoro-
Synthesis of dimers 4a and 4b. A solution of
cycloadduct 3a in anhydrous diethyl ether was concen-
trated in a vacuum at 20°C, and the residue was kept for
48 h at 20°C. The resulting dimer 4a was recrystallized
acetic anhydride was distilled over P O prior to use.
2
5
The structure of the compounds obtained was con- from hexane, mp 81–83°C. Cycloadduct 3b was kept
1
13
firmed by elemental analysis data, H and C NMR for 42 days at 20°C. The resulting dimer 4b was recrys-
spectra, and IR spectroscopy.
tallized from hexane, mp 81–82°C.
Trimethylstannyltrifluoroacetylacetylene 1. Trif-
luoroacetic anhydride (42.4 mL, 63 g, 0.30 mol) was
added in one portion to a solution of 100 g (0.28 mol)
of bis(trimethylstannyl)acetylene in 200 mL of tetrahy-
drofuran under stirring with a powerful magnetic stir-
rer; after the exothermic reaction was completed, the
mixture was allowed to stand overnight. The main por-
tion of the tetrahydrofuran was removed in a vacuum of
a water-jet pump on a water bath at 20°C. A reflux con-
denser was replaced by a distilling column with a
descending condenser and an adapter with a receiver
cooled with dry ice. The temperature of the water bath
was gradually increased to 90–95°C while the reaction
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