Synthesis of trimethylsilylpropynoyl chloride

Article abstract of DOI:10.1007/s11178-005-0367-8

Trimethylsilylpropynoic acid reacts with thionyl chloride to give a mixture of trimethylsilylpropynoyl chloride and 3-chloro-3-trimethylsilyl-2-propenoyl chloride whose ratio depends on the reaction conditions (temperature, reactant ratio). Dimethylformamide almost does not catalyze the reaction. Treatment of trimethylsilylpropynoic acid with oxalyl chloride in the presence of 0.04 equiv of DMF at room temperature ensures selective formation of trimethylsilylpropynoyl chloride (yield 80%).

Full text of DOI:10.1007/s11178-005-0367-8

Russian Journal of Organic Chemistry, Vol. 41, No. 10, 2005, pp. 1463–1466. Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 10, 2005,
pp. 1493–1496.
Original Russian Text Copyright © 2005 by Medvedeva, Andreev, Safronova, Afonin.
Dedicated to Full Member of the Russian Academy of Sciences
N.S. Zefirov on His 70th Anniversary
Synthesis of Trimethylsilylpropynoyl Chloride
A. S. Medvedeva, M. V. Andreev, L. P. Safronova, and A. V. Afonin
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: amedved@irioch.irk.ru
Received June 8, 2005
Abstract—Trimethylsilylpropynoic acid reacts with thionyl chloride to give a mixture of trimethylsilyl-
propynoyl chloride and 3-chloro-3-trimethylsilyl-2-propenoyl chloride whose ratio depends on the reaction
conditions (temperature, reactant ratio). Dimethylformamide almost does not catalyze the reaction. Treatment
of trimethylsilylpropynoic acid with oxalyl chloride in the presence of 0.04 equiv of DMF at room temperature
ensures selective formation of trimethylsilylpropynoyl chloride (yield 80%).
Carboxylic acid chlorides are widely used in or-
ganic synthesis as efficient acylating agents toward
various O-, N-, S-, and C-centered nucleophiles [1].
They are convenient reagents in the preparation of
hydroxamic acids [2], multicomponent syntheses of
2-propynyl amides [3], and syntheses of various hetero-
cyclic compounds, in particular substituted guanines
[4], dihydropyrazolones [5], 1,2,4-oxadiazoles [6],
thioxopiperidinones [7], etc. The presence of several
reaction centers in silicon-containing acetylenic car-
boxylic acid chlorides considerably extends their syn-
thetic potential. Electron-withdrawing effect of the
trimethylsilylethynyl group and the absence of steric
hindrances at the carbonyl carbon in such acid chlo-
rides should facilitate acylation of various nucleo-
philes. When necessary, the trimethylsilyl group can be
removed from the sp-hybridized carbon atom to afford
the corresponding products with a terminal triple bond.
The IR, UV, and 13C NMR spectra and relative
basicity of trimethylsilylpropynoyl chloride (II) were
described in [12, 13]; however, the conditions for the
synthesis of compound II were not given. We pre-
viously obtained trimethylsilylpropynoyl chloride (II)
by treatment of trimethylsilylpropynoic acid with
thionyl chloride [14], but the yield of II did not exceed
60%. In order to find optimal conditions for the pre-
paration of acid chloride II, in the present work we
examined the effects of the chlorinating agent nature
and other factors on the yield of the target product.
When acid I was heated with thionyl chloride, apart
from chloride II as the major product, we isolated
~20% of previously unknown 3-chloro-3-trimethyl-
silyl-2-propenoyl chloride (III) as a mixture of E and Z
isomers (Scheme 1). The isomer ratio varied from 1:1
to 3:1, depending on the reaction conditions; however,
we failed to reliably assign signals in the NMR spectra
to particular isomers even using NOESY technique.
Chlorides II and III were separated by vacuum dis-
tillation.
We previously studied 1,3-dipolar cycloaddition of
diazoalkanes to 3-trimethylsilyl-2-propynoyl chloride
[8] and acylation with the latter of butyl trimethylsilyl
sulfide, sodium thiolate [9], and a wide series of
amines [10]. Some Į-silylated acetylenic amides thus
obtained were found to exhibit fungicide, insecticide,
and antiphlogistic activity [11].
We examined the effects of such factors as reactant
ratio, temperature, reaction time, and catalyst on the
yields of the target product II and by-product III. The
reaction mixtures were analyzed by 1H NMR spectros-
Scheme 1.
O
O
Me3Si
Cl
SOCl2, 60°C, 15 min
+
Me3Si
Me3Si
Cl
O
OH
Cl
I
II
E,Z-III
1070-4280/05/4110-1463 © 2005 Pleiades Publishing, Inc.

MEDVEDEVA et al.
1464
Reactions of 3-trimethylsilyl-2-propynoic acid (I) with thionyl chloride and oxalyl chloride
Yield,a %
Temperature, Reaction
Reagent (equiv)
Conversion, %
Molar ratio II:III
°C
time, h
II
III
10
14
04
26
33
22
23
24
–
SOCl2 (2.5)
SOCl2 (2.5)b
SOCl2 (1.5)
SOCl2 (1.5)
SOCl2 (2.5)c
SOCl2 (2.5)
SOCl2 (2.5)
SOCl2 (5.0)
(COCl)2 (1.1)b
(COCl)2 (1.1)
(COCl)2 (1.1)
25
25
60
75
60
45
60
60
25
25
25
1.50
1.50
0.25
100.
0.25
0.10
0.25
0.25
0.50
0.50
20000.
045
059
024
096
096
086
098
099
100
007
076
035
045
020
070
036
064
075
075
100
007
076
3.5:1
3.2:1
0.5:1
2.7:1
0.1:1
2.9:1
3.3:1
3.1:1
–
–
–
–
–
a
b
c
According to the 1H NMR data.
In the presence of 0.04 equiv of DMF.
In the presence of 0.3 equiv of DMF.
copy, and the results are collected in table. The reac-
tion of acid I with thionyl chloride at room tem-
perature was ineffective: in the presence of 2.5 equiv
of SOCl2, the conversion did not exceed 45% in 1.5 h.
Raising the temperature strongly accelerates the proc-
ess. At 60°C, the reactant ratio being the same, the
conversion reached 98% in 15 min, and the yield of
chloride II was 75%. An important factor affecting the
efficiency of the process is the reactant ratio. Decrease
in the amount of thionyl chloride to 1.5 equiv dra-
matically reduces the conversion. The conversion may
be raised to 96% by heating at 75°C over a period of
1 h. It is known that dimethylformamide catalyzes
chlorination of carboxylic acids with thionyl chloride
[1]. However, no catalytic effect of DMF was observed
in the reaction under study: the conversion of I in-
creased only slightly in the presence of 0.04 equiv
of DMF (at room temperature). Raising the amount
of DMF to 0.3 equiv and the temperature to 60°C
resulted in increased conversion (96% in 15 min), but
the conversion was 98% in 15 min in the absence of
DMF. Moreover, the presence of DMF favors forma-
tion of the by-product: in the absence of catalyst, the
ratio of products II and III was about 3:1, while in the
presence of 0.3 equiv of DMF their ratio became ap-
proximately equimolar. These results are consistent
with published data on the reactions of propynoic acids
with SOCl2 in DMF, which were reported to produce
E,Z-isomeric 3-chloro-2-alkenoic acids, the E isomer
prevailing [15]. The minimal concentration of
3-chloro-3-trimethylsilyl-2-propenoyl chloride (III)
(ratio II:III = 5:1) was observed when the reaction
was carried out with 1.5 equiv of SOCl2, but in this
case the conversion was as low as 24% (60°C, 15 min).
The structure of acid chlorides II and III was con-
1
firmed by the IR and H, 13C, and 29Si NMR spectra
and elemental analyses. Compound III was isolated as
Scheme 2.
H+
O
O
OH
O
SOCl2
–HCl
Me3Si
Me3Si
O
Me3Si
O
OH
O
S
S
Cl
Cl
I
O
O
H
S
O
Cl–
Me3Si
O
Me3Si
+
HCl
+
SO2
Cl
Cl
Cl
II
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 10 2005

SYNTHESIS OF TRIMETHYLSILYLPROPYNOYL CHLORIDE
1465
Scheme 3.
Me3Si
OH
a
b
Cl
IV
O
O
Me3Si
Cl
SOCl2
–HCl
Me3Si
Cl
III
O
OH
O
I
Me3Si
Cl
II
silylpropynoyl chloride in high yield. With the use of
thionyl chloride as chlorinating agent, the yield of the
target product does not exceed 60%, for the process
is accompanied by formation of 3-chloro-3-trimethyl-
silyl-2-propenoyl chloride in ~20% yield.
a colorless liquid; on storage, it undergoes slow hy-
drolysis by the action of atmospheric moisture to give
previously unknown crystalline (E/Z)-3-chloro-3-tri-
methylsilyl-2-propenoic acid Me3Si(Cl)C=CHCOOH
(IV) (the fraction of one isomer is 98%).
In keeping with the known mechanism of formation
of acid halides by the action of thionyl chloride [1],
hydrogen chloride is released in both stages of the
process (Scheme 2). Chloride III could be formed by
addition of hydrogen chloride at the triple bond of tri-
methylsilylpropynoic acid I or chloride II (Scheme 3).
Insofar as compound III was not detected by 1H NMR
spectroscopy when pure chloride II was heated with
SOCl2 for 1.5 h at 60°C, we presumed that hydrogen
chloride adds at the triple bond of trimethylsilylpro-
pynoic acid I according to pathway a. The mechanism
of addition of hydrogen halides at the triple bond of
propynoic acids was studied in [16].
EXPERIMENTAL
The IR spectra were recorded on a Specord 75IR
13
29
spectrometer. The 1H, C, and Si NMR spectra were
measured on a Bruker DPX-400 instrument from solu-
tions in CDCl3 using cyclohexane as internal reference.
3-Trimethylsilyl-2-propynoyl chloride (II).
a. A mixture of 5.7 g (40 mmol) of acid I and 8.5 g
(71 mmol) of thionyl chloride was heated for 15 min.
Excess thionyl chloride was removed under reduced
pressure, and the residue was distilled at 53–55°C
(17 mm). Yield 3.5 g (55%). IR spectrum (film), Ȟ,
cm–1: 860, 1250 (SiMe3); 1750 (C=O); 2170 (CŁC).
1H NMR spectrum (CDCl3), į, ppm: 0.30 s (9H,
CH3Si). 13C NMR spectrum (CDCl3), įC, ppm: 149.40
(C=O); 103.40, 97.10 (CŁC). 29Si NMR spectrum
(CDCl3): įSi –12.50 ppm. Found, %: C 44.61; H 5.65;
Cl 22.10; Si 17.20. C6H9ClOSi. Calculated, %: C 44.85;
H 5.65; Cl 22.07; Si 17.48.
With the use of oxalyl chloride as chlorinating
agent, we succeeded in isolating trimethylsilylpropyn-
oyl chloride (II) in 80% yield, the conversion being
100% (Scheme 4). The reaction was complete in
30 min at room temperature in the presence of a small
excess (1.1 equiv of oxalyl chloride). In this case,
unlike the reaction with thionyl chloride, the presence
of 0.04 equiv of DMF as catalyst was necessary. As
follows from the data in table, in the absence of
catalyst the conversion sharply decreases (from 100 to
7% in 30 min). We succeeded in raising the conversion
to 76% only by considerable increase of the reaction
time (to 20 h).
b. A mixture of 2.9 g (20 mmol) of trimethylsilyl-
propynoic acid (I), 2.8 g (22 mmol) of oxalyl chloride,
and 0.04 equiv of DMF was kept for 30 min at room
temperature. The mixture was then distilled under re-
duced pressure to isolate 2.7 g (80%) of chloride II,
bp 49–51°C (16 mm).
(E,Z)-3-Chloro-3-trimethylsilyl-2-propenoyl
chloride (III) was isolated by distillation of the high-
boiling fraction (obtained as described above in a)
at 88–90°C (11 mm). Yield 1.6 g (20%). IR spectrum
(film), Ȟ, cm–1: 830, 1250 (SiMe3); 1640, 1660 (C=C);
Scheme 4.
(COCl)2, DMF
25°C, 30 min
O
O
Me3Si
Me3Si
OH
Cl
1
1740, 1770 (C=O). H NMR spectrum (CDCl3), į,
I
II
ppm: 0.30 s and 0.32 s (9H, CH3Si), 6.68 s and 7.02 s
(1H, C=CH). 13C NMR spectrum (CDCl3), įC, ppm:
159.75, 159.07 (C=CH); 137.33, 130.41 (C=CH);
167.67, 163.27 (C=O); –2.98, –2.09 (CH3Si). 29Si NMR
Thus the reaction of trimethylsilylpropynoic acid
with oxalyl chloride in the presence of DMF at room
temperature ensures selective formation of trimethyl-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 10 2005

MEDVEDEVA et al.
1466
8. Medvedeva, A.S., Russ. J. Org. Chem., 1996, vol. 32,
spectrum (CDCl3), įSi, ppm: 5.01, 3.95. Found, %:
C 36.40; H 5.68; Cl 35.70; Si 14.03. C6H10Cl2OSi. Cal-
culated, %: C 36.56; H 5.11; Cl 35.96; Si 14.25.
p. 272.
9. Medvedeva, A.S., Kalikhman, I.D., and Vyazan-
kin, N.S., Zh. Obshch. Khim., 1983, vol. 53, p. 1437.
(E,Z)-3-Chloro-3-trimethylsilyl-2-propenoic acid
(IV) (isomer ratio 98:2) was formed from chloride III
on storage. mp 91–92°C. IR spectrum (KBr), Ȟ, cm–1:
830, 1220 (SiMe3); 1570 (C=C); 1680 (C=O). 1H NMR
spectrum (CDCl3), į, ppm: major isomer: 0.33 s (9H,
CH3Si), 6.77 s (1H, C=CH), 11.04 br.s (1H, OH);
minor isomer: 0.38 s (9H, CH3Si), 6.43 s (1H, C=CH).
13C NMR spectrum (CDCl3), įC, ppm: 170.56,
165.73, 132.23, –0.62. 29Si NMR spectrum (CDCl3):
įSi 3.37 ppm. Found, %: C 39.91; H 6.09; Cl 19.28;
Si 15.29. C6H11ClO2Si. Calculated, %: C 40.33; H 6.20;
Cl 19.84; Si 15.72.
10. Safronova, L.P., Medvedeva, A.S., and Vyazankin, N.S.,
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