Table 2 (continued )
Entry
Aryl halides
Product
Yieldb (%)
19
64
76
20
a
Reaction conditions: ArI (1.0 mmol), Et3N (2.5 mmol), Pd(OAc)2
(1 mol%), ligand (2 mol%), water (50 mol%), DMF (2.0 mL), 115 1C,
6 h. Isolated yield. 48 h.
b
c
On the other hand, 4-methoxy-benzoic anhydride was obtained in
a high yield of 95% when water was replaced with 4-methoxy-
benzoic acid (eqn (5)), indicating that the latter participates in the
formation of the anhydride. However, 4-methoxy-benzoic acid
itself cannot give rise to the anhydride
Scheme 1 A plausible mechanism for anhydride formation.
and the Fundamental Research Funds for the Central
Universities (GK200902009).
Notes and references
1 M. A. Ogliaruso and J. F. Wolfe, Synthesis of Carboxylic Acids,
Esters and Their Derivatives, John Wiley & Sons, New York, 1991,
pp. 198–217.
2 E. C. Tayor, G. W. McLay and A. McKillop, J. Am. Chem. Soc.,
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ð4Þ
ð5Þ
3 W. Nakanishi, Y. Ikeda and H. Iwamura, J. Org. Chem., 1982,
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4 W. K. Fife and Z. D. Zhang, Tetrahedron Lett., 1986, 27, 4937.
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6 P. A. Clarke, N. E. Kayalech, M. A. Smith, J. R. Baker, S. J. Bird
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7 Y. Kawamura, Y. Sato, T. Horie and M. Tsukayama, Tetrahedron
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ð6Þ
with or without added water under the reaction conditions
(eqn (6)), suggesting that the anhydride is derived from the iodide
and 4-methoxy-benzoic acid or 4-methoxy-benzoate. In addition,
when the carbonylation of iodoanisole was performed under the
optimized conditions (Table 2) but quenched at 2 h reaction time,
the anhydride and iodoanisole were isolated in 38% and 54%
yield, respectively; the yield of 4-methoxy-benzoic was less than
2%, indicating that the acid is consumed once generated. Taking
these observations into account, a plausible mechanism is pre-
sented in Scheme 1. The main features are that water attacks the
Pd–acyl intermediate, resulting in the formation of a carboxylate
under the basic conditions employed; the carboxylate, being more
nucleophilic than water, reacts with a new Pd–acyl species, furnish-
ing the symmetric anhydride. Clearly, over-stoichiometric water
will lead to the formation of a carboxylic acid, whereas a sub-
stoichiometric amount encourages attack of the acyl by DMF.17
In summary, a convenient method for the preparation of
carboxylic acid anhydrides has been developed. The wide
scope, mild reaction conditions and high yields showcase the
potential of the method in chemical synthesis.
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14 For reviews see: (a) A. Brennfuhrer, H. Neumann and M. Beller,
¨
Angew. Chem., Int. Ed., 2009, 48, 4114; (b) C. F. J. Barnard,
Organometallics, 2008, 27, 5402.
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16 A trace amount of N,N-dimethylbenzamide was also observed.
DMF (99.5%) was used as received.
17 (a) Y.-Q. Wan, M. Alterman, M. Larhed and A. Hallberg, J. Org.
Chem., 2002, 67, 6232; (b) K. Hosoi, K. Nozaki and T. Hiyama,
Org. Lett., 2002, 4, 2849; (c) D. N. Sawant, Y. S. Wagh, K. D.
Bhatte and B. M. Bhanage, J. Org. Chem., 2011, 76, 5489.
18 Referring to water added to DMF plus background water from the
reaction system. As to how the water content was determined and
the detailed data, please see the ESIw.
We are grateful for the financial support of the National Science
Foundation (20602024), Program for Changjiang Scholars
and Innovative Research Team in University (IRT 1070)
19 For more details including ligands used, please see the ESIw.
c
1322 Chem. Commun., 2012, 48, 1320–1322
This journal is The Royal Society of Chemistry 2012