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Journal of the American Chemical Society
tion-assisted alkenyl C-H bond cleavage of 2-
1
2
3
4
5
6
7
8
REFERENCES
hydroxystyrene with Pd(OAc)2 along with coordination
of the second molecule of 2-hydroxystyrene 1 as its ce-
sium salt. Subsequently, alkenyl palladium(II) 4 under-
goes reversible nucleophilic carboxylation to afford pal-
ladium carboxylate intermediate A, which reacts with
another molecule of 2-hydroxystyrene 1 and base to give
coumarin with regeneration of the cyclometalated inter-
mediate 4.17 The shift of the carboxylation-
decarboxylation equilibrium to the carboxylation side
could be attributed to the lactonization process.18
(1) For reviews on transition metal-promoted CO2-fixation reac-
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(3) Fujiwara and co-workers reported Pd-catalyzed direct carboxy-
lation of arenes, albeit with low conversion, see; Sugimoto, H.; Kawa-
ta, I.; Taniguchi, H.; Fujiwara, Y. J. Organomet. Chem. 1984, 266,
C44.
Scheme 3. Proposed Mechanism
R
R
Pd(OAc)2
CO2
O
O
O
Pd
Cs2CO3
O
Cs Pd
O
1
Cs
O
– CO2
R
R
(4) Direct carboxylation reactions of C-H bonds without reducing
reagents were reported but they were limited to substrates that have
rather acidic protons (pKa of about 30), see ref 2a, 2b, 2c, and 2e.
(5) For recent selected examples of Pd-catalyzed carboxylation re-
actions with CO2, see; (a) Johansson, R.; Jarenmark, M.; Wendt, O. F.
Organometallics 2005, 24, 4500. (b) Yeung, C. S.; Dong, V. M. J. Am.
Chem. Soc. 2008, 130, 7826. (c) Takaya, J.; Iwasawa, N. J. Am. Chem.
Soc. 2008, 130, 15254. (d) Correa, A.; Martín, R. J. Am. Chem. Soc.
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C. D. J. Am. Chem. Soc. 2011, 133, 3280. (g) Feng, X.; Sun, A.;
Zhang, S.; Yu, X.; Bao, M. Org. Lett. 2013, 15, 108, and references
cited therein.
(6) For Pd-catalyzed alkenyl C-H bond olefination reactions via
alkenyl C-H bond cleavage, see; (a) Silva, M. J.; Gonçalves, J. A.;
Alves, R. B.; Howarth, O. W.; Gusevskaya, E. V. J. Organomet.
Chem. 2004, 689, 302. (b) Hatamoto, Y.; Sakaguchi, S.; Ishii, Y. Org.
Lett. 2004, 6, 4623. (c) Xu, Y.-H.; Lu, J.; Loh, T.-P. J. Am. Chem. Soc.
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352, 2445. (e) Xu, Y.-H.; Wang, W.-J.; Wen, Z.-K.; Hartley, J. J.;
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1822. (h) Yu, Y.-Y.; Niphakis, M. J.; Georg, G. I. Org. Lett. 2011, 13,
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Y.; Wang, F.; Jia, A.; Li, X. Chem. Sci. 2012, 3, 3231. (l) Wen, Z.-K.;
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M.; Kim, Y.; Hong, S. Chem. Commun. 2013, 49, 196. (o) Shang, X.;
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C-H bond arylation reactions via alkenyl C-H bond cleavage, see; (p)
Ge, H.; Niphakis, M. J.; Georg, G. I. J. Am. Chem. Soc. 2008, 130,
3708. (q) Würtz, S.; Rakshit, S.; Neumann, J. J.; Dröge, T.; Glorius,
F.; Angew. Chem., Int. Ed. 2008, 47, 7230. (r) Zhou, H.; Chung, W.-
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4076. (u) Li, C.; Zhang, Y.; Li, P.; Wang, L. J. Org. Chem. 2011, 76,
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Y.-Y.; Bi, L.; Georg, G. I. J. Org. Chem. 2013, 78, 6163. See also ref
6k, and 6m. For other examples including vinylpalladium species
generated via alkenyl C-H bond cleavage, see; (x) Giri, R.; Yu, J.-Q. J.
Am. Chem. Soc. 2008, 130, 14082. (y) Wang, H.; Guo, L.-N.; Duan,
X.-H. Org. Lett. 2012, 14, 4358.
4
A
O
OH
O
R
+ CsHCO3
CsOH
1
R
+ Cs2CO3
2
In conclusion, we have developed a catalytic direct
carboxylation of unactivated alkenyl C-H bond of 2-
hydroxystyrenes. This is the first example of Pd(II)-
catalyzed alkenyl C-H bond functionalization with nu-
cleophilic carboxylation. Furthermore, isolation of the
alkenyl palladium intermediate suggested the im-
portance of the regeneration step of intermediate 4 in
this reaction. Further studies to reveal the detailed
mechanism are in progress.
ASSOCIATED CONTENT
Supporting Information. Preparative methods, spectral
and analytical data for compound 1, 2, 3a, 4a, and crystal-
lographic data (CIF). This material is available free of
AUTHOR INFORMATION
Corresponding Author
ACKNOWLEDGMENT
This research was supported by Grant-in-Aids for Scientific
Research from the Ministry of Education, Culture, Sports,
Science, and Technology of Japan and ACT-C program
from the Japan Science and Technology Agency. K.S. has
been granted a Research Fellowship of the Japan Society
for the Promotion of Science for Young Scientists.
(7) Recently, Alper’s group reported Pd-catalyzed oxidative cy-
clocarbonylation of 2-hydroxystyrenes with carbon monoxide for the
synthesis of coumarins, see; Ferguson, J.; Zeng, F.; Alper, H. Org.
Lett. 2012, 14, 5602.
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