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This research was supported by a Grant-in-Aid for Scientific
Research from MEXT, Japan, and ACT-C from JST. T. S. thanks
JSPS for a fellowship.
Notes and references
1
For recent reviews on catalytic carboxylation of organic compounds,
see: (a) Z. Wenzhen and L. Xiaobing, Chin. J. Catal., 2012, 33, 745–756;
(
b) Y. Tsuji and T. Fujihara, Chem. Commun., 2012, 48, 9956–9964;
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Scheme 1 Proposed mechanism.
2
010, 39, 3347–3357; (g) T. Sakakura, J.-C. Choi and H. Yasuda, Chem. Rev.,
007, 107, 2365–2387.
Fujiwara reported the first example of transition metal-promoted
carboxylation of benzene with 1 atm of CO , although the efficiency
was not satisfactory (TON = ca. 1.3). See: H. Sugimoto, I. Kawata,
H. Taniguchi and Y. Fujiwara, J. Organomet. Chem., 1984, 266, C44–C46.
Examples of metal-catalyzed direct carboxylation of simple arenes
using CO or HCOOH: (a) T. Itahara, Chem. Lett., 1982, 1151–1152;
2
2
3
2
(
b) W. Lu, Y. Yamaoka, Y. Taniguchi, T. Kitamura, K. Takaki and
Y. Fujiwara, J. Organomet. Chem., 1999, 580, 290–294; (c) V. V. Grushin,
W. J. Marshall and D. L. Thorn, Adv. Synth. Catal., 2001, 343, 161–165;
Scheme 2 KIE experiment.
(
(
4
2
d) S. Ohashi, S. Sakaguchi and Y. Ishii, Chem. Commun., 2005, 486–488;
e) K. Sakakibara, M. Yamashita and K. Nozaki, Tetrahedron Lett., 2005,
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4 (a) I. I. F. Boogaerts and S. P. Nolan, J. Am. Chem. Soc., 2010, 132,
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674–8677; (c) L. Zhang, J. Cheng, T. Ohishi and Z. Hou, Angew.
applicable to both electron-rich and -deficient arenes whereas
previously reported acid- or base-promoted reactions are limited
to either one of them. (2) Preferential carboxylation with regio-
selectivities different from those previously reported is possible.
8
8
(
3) The reaction proceeds under atmospheric pressure of CO
2
whereas
Chem., Int. Ed., 2010, 49, 8670–8673; (d) I. I. F. Boogaerts and
S. P. Nolan, Chem. Commun., 2011, 47, 3021–3024; (e) H. Inomata,
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A. S. Lindsey and H. Jeskey, Chem. Rev., 1957, 57, 583–620.
For selected examples of Lewis acid-promoted electrophilic carboxyla-
tion, see: (a) G. A. Olah, B. T o¨ r o¨ k, J. P. Joschek, I. Bucsi, P. M. Esteves,
G. Rasul and G. K. S. Prakash, J. Am. Chem. Soc., 2002, 124,
Al-mediated electrophilic carboxylation requires high pressure.
Therefore, this rhodium-catalyzed protocol demonstrates a new
approach toward direct carboxylation of simple arenes utilizing
5
6
7
CO
2
as a C1 source.
A tentatively proposed reaction mechanism is shown in
Scheme 1. The reaction starts with generation of a methyl-
rhodium(I) complex A from 1c and AlMe1.5(OEt)1.5 followed by
oxidative addition of an sp C–H bond of a simple arene to A,
giving an aryl(hydride)(methyl)rhodium(III) intermediate B.
Reductive elimination of methane from B affords a highly
reactive arylrhodium(I) complex C. Nucleophilic addition of
C to CO
converted to methylrhodium(I) A through transmetallation with
AlMe1.5(OEt)1.5
To obtain mechanistic insights, competitive reactions of C
and C were examined in the same vessel. After esterification
with benzyl bromide, the KIE value ([6a-d ]/[6a-d ]) at the point of
1
1379–11391; (b) K. Nemoto, S. Onozawa, N. Egusa, N. Morohashi
and T. Hattori, Tetrahedron Lett., 2009, 50, 4512–4514; (c) K. Nemoto,
H. Yoshida, N. Egusa, N. Morohashi and T. Hattori, J. Org. Chem., 2010,
75, 7855–7862; (d) P. Munshi, E. J. Beckman and S. Padmanabhan, Ind.
Eng. Chem. Res., 2010, 49, 6678–6682.
2
8
Base-promoted carboxylation reactions of acidic C–H bonds of
aromatic compounds were also reported, see: (a) O. Vechorkin,
N. Hirt and X. Hu, Org. Lett., 2010, 12, 3567–3569; (b) K. Inamoto,
N. Asano, Y. Nakamura, M. Yonemoto and Y. Kondo, Org. Lett., 2012,
1
6
1
7
2
gives a rhodium(I) benzoate complex D, which is
1
4, 2622–2625; (c) W.-J. Yoo, M. G. Capdevila, X. Du and
1
8
.
S. Kobayashi, Org. Lett., 2012, 14, 5326–5329.
6
H
6
9 For a review on the catalytic C–H bond functionalization without the
assistance of a directing group, see: (a) N. Kuhl, M. N. Hopkinson,
J. Wencel-Delord and F. Glorius, Angew. Chem., Int. Ed., 2012, 51,
10236–10254. For recent specified reviews on these subjects, see: For
coupling: (b) A. Lei, W. Liu, C. Liu and M. Chen, Dalton Trans., 2010, 39,
10352–10361; for the oxidative Heck reaction: (c) J. L. Bras and J. Muzart,
Chem. Rev., 2011, 111, 1170–1214; for borylation and silylation:
6 6
D
0
5
1
h reaction time was estimated to be 5.5, which suggests that the
19
C–H bond activation step is the rate-determining step (Scheme 2).
In conclusion, we have developed a novel method for direct
carboxylation of simple arenes with 1 atm CO through a
rhodium-catalyzed C–H bond activation without the assistance
of a directing group. This reaction demonstrates wide generality
and intriguing regioselectivity, which were not achieved by using
previous acid- or base-promoted protocols. These findings are
highly promising to expand synthetic utility of the direct
(d) I. A. I. Mkhalid, J. H. Barnard, T. B. Marder, J. M. Murphy and
2
J. F. Hartwig, Chem. Rev., 2010, 110, 890–931; (e) J. F. Hartwig, Acc. Chem.
Res., 2012, 45, 864–873.
0 AlMe1.5(OEt)1.5 was prepared by adding 2 equiv. of EtOH to a
1
3
solution of AlMe in hexane (1.4 M) at 0 1C followed by removal of
the solvent. The obtained slightly sticky solid was employed for the
reaction. Such a composition was also reported by other researchers;
J. Turunen, T. T. Pakkanen and B. L ¨o fgren, J. Mol. Catal., 1997, 123,
35–42. See the ESI† for details.
carboxylation of simple arenes even though a stoichiometric 11 Such effects of polar cosolvents are proposed in a cobalt-catalyzed
C–H bond activation reaction, see: Q. Chen, L. Ilies and E. Nakamura,
J. Am. Chem. Soc., 2011, 133, 428–429.
2 Formation of acetic acid was also detected. As the rate-determining
amount of aluminum reagent is required at present. Further
studies on improvement of the efficiency of the reaction and
1
investigations on the reaction mechanism are in progress.
step is the C–H activation step, the amount of CO such as the volume
2
14362 | Chem. Commun., 2014, 50, 14360--14363
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