Carboxylation of alkynylsilanes with carbon dioxide mediated by cesium fluoride in DMSO

Article abstract of DOI:10.1039/c3ob40760h

The facile syntheses of a variety functionalized propiolic acids were achieved by carboxylation of alkynylsilanes with carbon dioxide mediated by cesium fluoride under ambient conditions. This journal is The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ob40760h

Organic &
Biomolecular Chemistry
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Carboxylation of alkynylsilanes with carbon dioxide
mediated by cesium fluoride in DMSO†
Cite this: Org. Biomol. Chem., 2013, 11,
3773
Misato Yonemoto-Kobayashi, Kiyofumi Inamoto, Yoshiyuki Tanaka and
Yoshinori Kondo*
Received 16th April 2013,
Accepted 7th May 2013
DOI: 10.1039/c3ob40760h
www.rsc.org/obc
The facile syntheses of a variety functionalized propiolic acids inexpensive, non-toxic and has promising renewable charac-
were achieved by carboxylation of alkynylsilanes with carbon ter.9 In connection with our recent interest on carboxylation of
dioxide mediated by cesium fluoride under ambient conditions.
alkynes,9e we wish to report the first development of a direct
incorporation of CO2 into alkynylsilanes mediated by cesium
fluoride, affording propiolic acids under ambient conditions.10
First, the reaction of 1-phenyl-2-trimethylsilylacetylene (1a)
with CO2 (balloon) was examined to screen the optimized reac-
tion conditions. The reaction in THF in the presence of a stoi-
chiometric amount of cesium fluoride as an activating agent
was sluggish, and only slight progress of carboxylation was
observed (Table 1, entry 1). We next focused our attention on
solvent effect. It was found that polar solvents played the role
of increasing the reaction rate (entries 4–6). Dimethyl sulfoxide
(DMSO) was proved to be the best solvent, allowing carboxyla-
tion with CO2 at room temperature to yield phenylpropiolic
C–C bond formation via the alkynylation of carbonyl com-
pounds is among the most powerful processes in recent
organic synthesis, since it provides various propargylic com-
pounds as versatile building blocks.1 Among the reported
methods, base promoted cleavage and functionalization of the
C–Si bond of silylacetylenes is exceedingly useful for selective
bond formations.2 Kuwajima and Nakamura first reported
nucleophilic addition of trimethylsilylacetylenes to aldehydes
and ketones catalyzed by tetrabutylammonium fluoride
(TBAF), affording the corresponding propargylic alcohols.3 In
addition, several groups reported similar alkynylation reac-
tions catalyzed by CsF,4a tetrabutylammonium triphenyl-
difluorosilicate
(TBAT),4b
mixed
salts
(CsF–CsOH),4c
phosphine,4d ammonium phenoxide4e and proazaphospha-
trane.4f Shioiri et al. used a quaternary ammonium fluoride
catalyst to synthesize branched Morita–Baylis–Hillman-type
adducts from 1-phenyl-2-trimethylsilylacetylene with aromatic
aldehydes.5 Scheidt successfully employed potassium ethoxide
as a catalyst for the addition of trialkoxysilylalkynes to alde-
hydes, ketones, and imines.6 Verkade’s group developed TBAF
catalyzed alkynylation of aldehydes and trifluoromethyl
ketones at room temperature.7 We also found that the use of
catalytic Schwesinger’s phosphazene base (t-Bu-P4 base) pro-
motes the addition of silylacetylenes to benzophenone and
styrene oxide.8 However, in all these cases, highly reactive car-
bonyl compounds such as aldehydes, ketones and imines have
been employed as electrophiles.
a
Table 1 Carboxylation of 1-phenyl-2-trimethylsilylacetylene with CO2
Entry
Base (X eq.)
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
CsF (1.2 eq.)
CsF (1.2 eq.)
CsF (1.2 eq.)
CsF (1.5 eq.)
THF
DME
Toluene
CH3CN
DMF
24
6
6
6
6
3
0
0
86
62
96 (96)
72
Trace
4
8
CsF (1.2 eq.)
6
7
8
9
CsF (1.2 eq.)
KF (1.2 eq.)
K2CO3 (1.2 eq.)
Cs2CO3 (1.2 eq.)
TBAF (THF solution)
(1.2 eq.)
DMSO
DMSO
DMSO
DMSO
DMSO
6
24
6
6
6
Recently, much attention has been focused on carbon
dioxide as a C1 chemical source because it is readily available,
10
11
TBAF·3H2O (1.2 eq.)
CsF (1.5 eq.)
DMSO
DMSO
6
3
17
(94)
12c
a Reactions were carried out on a 0.3 mmol scale. b Yields were
determined by 1H-NMR. Isolated yields are in parentheses. c Reaction
was carried out on a 4 mmol scale: 1-phenyl-2-trimethylsilylacetylene
(4.0 mmol), CsF (1.5 equiv., 6.0 mmol), CO2 balloon, DMSO (10 mL),
3 h.
Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3Aoba, Aramaki,
Aoba-ku, Sendai 980-8578, Japan. E-mail: ykondo@m.tohoku.ac.jp;
Fax: +81-22-795-5917; Tel: +81-22-795-6804
†Electronic supplementary information (ESI) available: Experimental procedures
and spectral/analytical data. See DOI: 10.1039/c3ob40760h
This journal is © The Royal Society of Chemistry 2013
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reaction could be scaled up from 0.3 mmol to 4 mmol without
significant loss of yield with 1.5 equivalent of CsF (entry 12).
The scope with respect to aryl and alkyl substituted alkynyl-
silanes 1a–q was then explored under the optimized reaction
conditions: 1.2 equiv. of CsF, CO2 balloon, DMSO, room temp-
erature. As shown in Table 2, carboxylation of electron-donat-
ing or electron-withdrawing group substituted phenyl- and
naphthyl-alkynylsilanes smoothly proceeded to afford the
desired carboxylic acids (2a–m) in good to excellent yields. It
should to be noted that this CsF promoted reaction system
showed good tolerance toward a variety functional groups such
as hydroxyl (1e), halogen (1f–h), cyano (1j), nitro (1k) and ester
(1l). Substrates bearing a heteroaromatic ring were also applied
to the reaction system. While 2-thiophenyl-alkynylsilanes (1n)
proceeded efficiently to give 2n in 94%, the reaction of 3-pyridyl-
ethynylsilane (1o) did not give the desired product. Since loss
of the product in the workup process cannot be excluded,
methyl iodide was used for quenching and the yield of the
corresponding ester 3o was improved to 66% yield (eqn (1)).
Table 2 Cesium fluoride mediated carboxylation of alkynylsilanes with carbon
dioxidea
Entry
1
Alkynylsilane
Yieldb (%)
1a
1b
1c
1d
96 (2a)
2
3
4
72 (2b)
85 (2c)
Quant. (2d)
5
1e
72 (2e)
6
1f
84 (2f)
7
1g
1h
1i
70 (2g)
78 (2h)
80 (2i)
ð1Þ
8
9
Alkyl substituted trimethylsilylacetylenes also underwent
the reaction to afford the corresponding carboxylic acid (2p
and 2q) in good to excellent yield, when 2 equivalents of
cesium fluoride were used.
We next tested alkynoate synthesis through carboxylation of
alkynylsilanes followed by alkylation with alkyl halide
(Table 3).12 Methyl ester 3aa was obtained in 81% when the
10
11
12
13
1j
Quant. (2j)
51 (2k)
90 (2l)
1k
1k
1m
78 (2m)
Table 3 Cesium fluoride mediated carboxylation of alkynylsilanes with carbon
dioxidea
14
15
1n
1o
94 (2n)
ND (2o)
16c
17c
1p
1q
98 (2p)
78 (2q)
Entry
1
RX (1.2 eq.)
Mel
Product
Yieldb (%)
81
3aa
3ab
a Reactions were carried out on a 0.3 mmol scale. b Isolated yield.
c 2.0 equiv. of CsF was used.
2
3
77
63
3ac
3ad
acid (2a) in 96% (entry 6). The effect of base was also investi-
gated in DMSO.11 Compared to cesium fluoride, potassium flu-
oride turned out to be less effective (entry 7). Carbonate salts
did not show promoting effect (entries 8 and 9). When tetra-
butylammonium fluoride (TBAF) was used for the reaction, 2a
4
69
was obtained in low yield (entries 10 and 11). Moreover, the a Reactions were carried out on a 0.3 mmol scale. b Isolated yield.
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carboxylation was first carried out and then 1.2 equivalent of
methyl iodide was added into the reaction mixture (entry 1). The
reaction using allyl bromide, benzyl bromide and n-butyl
bromide showed excellent performance as well to give the corres-
ponding esters 3ab–ad in good yields (entries 2–4; 63–77%).
In summary, we have developed cesium fluoride mediated
carboxylation of alkynyl silanes with carbon dioxide under
ambient conditions, providing various propiolic acid deriva-
tives successfully in good to excellent yields. Further studies to
8 M. Ueno, C. Hori, K. Suzawa, M. Ebisawa and Y. Kondo,
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9 (a) T. Sakakura, J.-C. Choi and H. Yasuda, Chem. Rev., 2007,
107, 2365–2387; (b) I. Omae, Coord. Chem. Rev., 2012, 256,
1384–1405; (c) S. N. Riduan and Y. Zhang, Dalton Trans.,
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Y. Kondo, Org. Biomol. Chem., 2012, 10, 1514–1516.
extend the scope of this process to alkynylsilane derivatives are 10 For related carboxylation of C-silyl compounds using CO2,
currently underway.
see: (a) Lewis acid mediated carboxylation of aryl- and allyl-
silanes: T. Hattori, Y. Suzuki and S. Miyano, Chem. Lett.,
2003, 454–455; (b) KF catalyzed carboxylation of arylsilanes:
F. Effenberger and W. Spiegler, Chem. Ber., 1985, 118,
3872–3899; (c) CsF mediated carboxylation of 1-cyano-1-
trimethylsilyl-cyclopropane: M. Ohno, H. Tanaka,
M. Komatsu and Y. Ohshiro, Synlett, 1991, 919–920; (d) CsF
mediated carboxylation of (perfluoroalkyl)trimethylsily-
lane: R. P. Singh and J. M. Shreeve, Chem. Commun., 2002,
1818–1819; (e) Benzylic C–H silylation and fluoride-
mediated carboxylation: T. Mita, K. Michigami and Y. Sato,
Org. Lett., 2012, 14, 3462–3465.
Acknowledgements
This work was partly supported by a Grant-in-Aid for Scientific
Research (B) (No. 23390002), a Grant-in-Aid for Challenging
Exploratory Research (No. 23659001) and a Grant-in-Aid for
Young Scientists (B) (No. 23790002) from Japan Society for
the promotion of Science, and a Grant-in-Aid for Scientific
Research on Innovative Areas “Advanced Molecular Transfor-
mations by Organocatalysis” (No. 23390002) from The Ministry
of Education, Culture, Sports, Science and Technology, Japan.
11 General procedure for carboxylation of the alkynylsilanes
with CO2: a dried and CO2 (balloon) infused Schlenk-flask,
equipped with a magnetic stirrer and a septum, was
charged with CsF (54.7 mg, 0.36 mmol) in DMSO
(0.75 mL). Alkynylsilane (0.3 mmol) was added to the reac-
tion mixture and the reaction was stirred at room temp-
erature for 3 h. The reaction mixture was diluted with water
(30 mL) and extracted with CH2Cl2 (2 × 10 mL). The
aqueous layer was acidified (>pH 1) with aqueous HCl
(6 M) at 0 °C and then extracted with diethyl ether (4 ×
20 mL). The combined organic layers were dried over
Na2SO4. The solvent was removed under vacuum to afford
pure product.
12 General procedure for preparation of alkynoates: a dried
and CO2 (balloon) infused Schlenk-flask, equipped with a
magnetic stirrer and a septum, was charged with CsF
(54.7 mg, 0.36 mmol) in DMSO (0.75 mL). Alkynylsilane
(0.3 mmol) was added to the reaction mixture and the reac-
tion was stirred at room temperature for 3 h. Alkyl halide
(0.36 mmol) was added to the reaction mixture and the
reaction was stirred at room temperature for 1 h. Saturated
aqueous NH4Cl (5 mL) was added and the whole mixture
was extracted with AcOEt (10 mL × 3). The combined
organic layers were washed with brine (10 mL) and dried
over MgSO4. The organic phase was concentrated under
reduced pressure and the crude material was purified by
silica gel column chromatography to give the corres-
ponding ester.
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