C O M M U N I C A T I O N S
method,3 this approach enables carboxylation of functional group
compatible aliphatic nucleophiles.19
Table 2. Pd-Catalyzed Arylzinc Carboxylations
In summary, we have presented a novel catalytic strategy for
carbon dioxide incorporation. Aresta’s complex can catalyze the
cross-coupling of organozinc reagents with CO2, and Pd(OAc)2 is
shown to be a convenient catalyst precursor for carbon dioxide
activation. We are further investigating the mechanism of this
process and plan to use this concept toward asymmetric carboxylation.
Acknowledgment. We thank the University of Toronto, the
Canada Foundation for Innovation, Ontario Research Foundation,
and the Natural Sciences and Research Council (NSERC) of Canada
for financial support (through a Discovery Grant and a postgraduate
Julie Payette Research Scholarship).
entry
functional group (FG)
yield (%)a
1
2
3
4
5
6
7
8
none
90b,c
90
97
p-OMe
m-OMe
o-OMe
p-OAc
p-Me
p-CF3
p-Cl
p-F
80
97d
81e
90
88
94
73
Supporting Information Available: General procedures for car-
boxylations, organozinc synthesis, catalyst preparation, spectroscopic
data. This material is available free of charge via the Internet at http://
pubs.acs.org.
9
10
11
12
p-CN
p-COMe
p-COOEt
75
76e
a Isolated yields. b Organozinc solution in THF. c With 1 mol % of
[Pd], 2 mol % of PCy3. d Isolated as 4-hydroxybenzoic acid after
saponification with 1 M NaOH. e With 5 mol % of [Pd], 10 mol % of
PCy3.
References
(1) Recent reviews: (a) Sakakura, T.; Choi, J.-C.; Yasuda, H. Chem. ReV. 2007,
107, 2365. (b) Louie, J. Curr. Org. Chem. 2005, 9, 605. (c) Aresta, M.;
Dibenedotto, A. Dalton Trans. 2007, 2975.
Table 3. Ni-Catalyzed Aryl- and Alkylzinc Carboxylations
(2) Carboxylation of organocuprates: (a) Ebert, G. W.; Juda, W. L.; Kosa-
kowski, R. H.; Ma, B.; Dong, L.; Cummings, K. E.; Phelps, M. V. B.;
Mostafa, A. E.; Luo, J. J. Org. Chem. 2005, 70, 4314. (b) Ukai, K.; Aoki,
M.; Takaya, J.; Iwasawa, N. J. Am. Chem. Soc. 2006, 128, 8706.
(3) Review of organozinc reagents: Knochel, P.; Calaza, M. I.; Hupe, E. In
Metal-Catalyzed Cross-Coupling Reactions, 2nd ed.; de Meijere, A.,
Diederich, F., Eds.; Wiley-VCH: Weinhelm, Germany, 2004; Vol. 1,
Chapter 11.
entry
RZnX
yield(%)a
(4) Carbonylation of C-X bonds is a complimentary strategy: Handbook of
Organopalladium Chemistry for Organic Synthesis; Negishi, E.-I., Ed.; John
Wiley & Sons, Inc.: New York, 2002; Part VI.
1
2
3
4
5
6
7
PhZnBr
74b
80
90
80
92
75
86
PhZnPhc
(5) (a) Aresta, M.; Nobile, C. F.; Albano, V. G.; Forni, E.; Manassero, M.
J.Chem.Soc.,Chem.Commun.1975,15,636.Spectroscopicinvestigations:(b)
Aresta, M.; Nobile, C. F. J. Chem. Soc., Dalton Trans. 1977, 708.
Stoichiometric reactions: (c) Aresta, M.; Gobetto, R.; Quaranta, E.;
Tommasi, I. Inorg. Chem. 1992, 31, 4286. (d) Tommasi, I.; Aresta, M.;
Giannoccaro, P.; Quaranta, E.; Fragale, C. Inorg. Chim. Acta 1998, 272,
38. (e) Wright, C. A.; Thorn, M.; McGill, J. W.; Sutterer, A.; Hinze, S. M.;
Prince, R. B.; Gong, J. K. J. Am. Chem. Soc. 1996, 118, 10305.
(6) Yin, X.; Moss, J. R. Coord. Chem. ReV. 1999, 181, 27.
n-C5H11ZnBr
Ph(CH2)2ZnBr•LiCld
Cl(CH2)3ZnI•LiCld
AcO(CH2)4ZnBr•LiCld
EtOOC(CH2)4ZnBr•LiCld
a Isolated yields. b With 10 mol % of Ni(COD)2 and 20 mol % of
PCy3. c In situ prepared PhZnEt reacts poorly. d See ref 18 for
preparation.
(7) Other Ni(0)-catalyzed carboxylations: (a) Takimoto, M.; Nakamura, Y.;
Kimura, K.; Mori, M. J. Am. Chem. Soc. 2004, 126, 5956. (b) Tekavec,
T. N.; Arif, A. M.; Louie, J. Tetrahedron 2004, 60, 7431.
(8) Transmetalation in analogous six-membered nickelocycles has been
reported: Bercot, E.; Rovis, T. J. Am. Chem. Soc. 2005, 127, 247.
(9) (a) Olah, G. A.; To¨ro¨k, B.; Joshek, J. P.; Busci, I.; Esteves, P. M.; Rasul,
G.; Prakash, G. K. S. J. Am. Chem. Soc. 2002, 124, 11379. (b) Nemoto,
K.; Yoshida, H.; Suzuki, Y.; Morohashi, N.; Hattori, T. Chem. Lett. 2006,
35, 820.
investigate the scope of our carboxylation (Table 2). Arylzinc reagents
prepared by this route reacted well with Pd(OAc)2 as the precatalyst,16
although higher loadings were required. Both electron-rich and
electron-poor organozinc reagents were carboxylated in good to
excellent yields (entries 1-9), while aromatic rings bearing π-acceptors
gave moderate yields (entries 10-12). Notably, substituents at ortho,
meta, and para positions can be tolerated (entries 2-4). The carboxy-
lation of arylzinc bromides displayed a significant scope, allowing
functionalities traditionally incompatible with Grignard reagents (e.g.,
ketones, esters, nitriles; entries 10-12).2 A heteroaromatic reagent
could also be effectively carboxylated (eq 1).
(10) Two accounts of a Ni(η2-CO2) intermediate in catalysis have been
reported: (a) De´rien, S.; Clinet, J.-C.; Dun˜ach, E.; Pe´richon, J. J. Org. Chem.
1993, 58, 2578. (b) Walther, D.; Scho¨nberg, H.; Dinjus, E.; Sieler, J. J.
Organomet. Chem. 1987, 334, 377.
(11) (a) Jolly, P. W.; Jonas, K.; Kruger, C.; Tsay, Y.-H. J. Organomet. Chem.
1971, 33, 109. (b) Darensbourg, M. H.; Ludwig, M.; Riordan, C. G. Inorg.
Chem. 1989, 28, 1630.
(12) Pd(η2-CO2)(PMePh2)2 is known: Sakamoto, M.; Shimizu, I.; Yamamoto,
A. Organometallics 1994, 13, 407. Pd(η2-CO2)(PCy3)2 could not be
observed spectroscopically.
(13) Homocoupling is one possibility for reduction: (a) Organ, M. G.; Avola,
S.; Dubovyk, I.; Hadei, N.; Kantchev, E. A. B.; O’Brien, C. J.; Valente, C.
Chem.—Eur. J. 2006, 12, 4749. (b) Wang, J.-X.; Wang, K.; Zhao, L.; Li,
H.; Fu, Y.; Hu, Y. AdV. Synth. Catal. 2006, 348, 1262.
(14) See Supporting Information for details.
(15) (a) Fillon, H.; Gosmini, C.; Pe´richon, J. J. Am. Chem. Soc. 2003, 125,
3867. Arylzinc reagents can also be prepared by (i) insertion of highly
active zinc to C-Br bonds: (b) Rieke, R. D. Aldrichimica Acta 2000, 33,
52or (ii) transmetalation: (c) Milne, J. E.; Buchwald, S. L. J. Am. Chem.
Soc. 2004, 126, 13028. (d) Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2001,
123, 2719.
(16) Ni(COD)2 was not a suitable precatalyst. See Supporting Information.
(17) The use of Pd(OAc)2 in alkylzinc carboxylation resulted in lower yields.
(18) Alkylzinc reagent preparation: Krasovskiy, A.; Malakhov, V.; Gavryushin,
A.; Knochel, P. Angew. Chem., Int. Ed. 2006, 43, 6040.
Complimentary to our Pd-based protocol,17 we found that, under
Ni catalysis, both aromatic and aliphatic zinc reagents could be
tolerated (Table 3). Commercially available PhZnBr, Ph2Zn, and
n-C5H11ZnBr underwent CO2 incorporation to produce the corre-
sponding carboxylic acids in good yields (entries 1-3). Alkylzinc
reagents (prepared by Knochel’s method)18 bearing various func-
tionality (e.g., Ph, Cl, AcO, EtCOO substituents) were also well-
tolerated (entries 4-7). In contrast to Iwasawa’s Rh-catalyzed
(19) Carboxylation of allylstannanes is known but is subject to significant
scrambling: (a) Shi, M.; Nicholas, K. M. J. Am. Chem. Soc. 1997, 119,
5057. (b) Johansson, R.; Wendt, O. F. Dalton Trans. 2007, 488.
JA803435W
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