Table 3 Cu(I)-catalyzed aerobic oxidative homocoupling reaction of
oxazoles and thiazolesa
2 (a) J. C. Freys, G. Bernardinelli and O. S. Wenger, Chem. Commun.,
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4 J. S. Casas, A. Castineiras, Y. Parajo
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, A. Sa
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´
nchez-
Gonzalez and J. Sordo, Polyhedron, 2005, 24, 1196.
´
5 T. Sekine, Y. Higuchi, T. Yamada and I. Murakoshi, Chem.
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7 (a) D. Monguchi, A. Yamamura, T. Fujiwara, T. Somete and
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9 Reactions using sodium phenoxide, pyridine or potassium tert-
butoxide as the additive also resulted in no reaction.
10 An example for deacetylation of 1-acetylimidazole, see:
W. Langenbeck and R. Mahrwald, Chem. Ber., 1957, 90, 2423. An
example for acetyl transfer of 1-acetylimidazole, see: A. M. Shultz,
O. K. Farha, J. T. Hupp and S. T. Nguyen, J. Am. Chem. Soc., 2009,
131, 4204.
Entry
1
Substrate
Yieldb (%)
84
2
3
4
91
81
91
11 By the stoichiometric reaction of CuCl with sodium 5-methyl-2-
pyridonate (L8) in p-xylene under reflux, a copper compound 21
with compositional formula of CuC6H6NO (confirmed by element
analysis), which was consistent with that of the supposed active
species A, was isolated in 89% yield. Although the structure of 21
has not been completely elucidated so far, we speculate that 21
would be identical to the active species A, because catalytic
homocoupling reaction of 1 using 21 as a catalyst (1.0 mol%) gave
1a in 92% yield. For details, see the ESIw.
12 For Pd-catalyzed carboxylate-ligand-promoted C–H activation:
(a) D. Garcia-Cuadrado, A. A. C. Braga, F. Maseras and A. M.
Echavarren, J. Am. Chem. Soc., 2006, 128, 1066; (b) M. Lafrance,
C. N. Rowley, T. K. Woo and K. Fagnou, J. Am. Chem. Soc., 2006,
128, 8754; (c) D. Lapointe and K. Fagnou, Chem. Lett., 2010, 1118 and
references therein.
5
6
92
98
a
The reaction was carried out with oxazoles or thiazoles (2.0 mmol),
CuCl (0.02 mmol, 1.0 mol%) and L8 (0.04 mmol, 2.0 mol%) in p-xylene
b
(4 mL) at 140 1C for 20 hours. Isolated yield.
of CuCl (1.0 mol%) and sodium 2-pyridonate ligand (2.0 mol%),
a variety of biazoles were synthesized in good to excellent yields
using air as a green oxidant.
13 For Cu-catalyzed carboxylate-ligand-promoted C–H activation:
M. Kitahara, N. Umeda, K. Hirano, T. Satoh and M. Miura,
J. Am. Chem. Soc., 2011, 133, 2160.
14 For the formation of Cu(III) intermediates in copper-catalyzed
oxidative couplings, see: (a) A. E. King, L. M. Huffman,
A. Casitas, M. Costas, X. Ribas and S. S. Stahl, J. Am. Chem.
Soc., 2010, 132, 12068; (b) A. Casitas, A. E. King, T. Parella,
M. Costas, S. S. Stahl and X. Ribas, Chem. Sci., 2010, 1, 326;
(c) B. Chen, X. Hou, Y. Li and Y. Wu, J. Am. Chem. Soc., 2011,
133, 7668.
Notes and references
1 (a) S. B. Park and H. Alper, Org. Lett., 2003, 5, 3209; (b) S. B. Park
and H. Alper, Chem. Commun., 2004, 1306; (c) J. Xiao,
B. Twamley and J. M. Shreeve, Org. Lett., 2004, 6, 3845;
(d) J. Xiao and J. M. Shreeve, J. Org. Chem., 2005, 70, 3072.
c
12878 Chem. Commun., 2011, 47, 12876–12878
This journal is The Royal Society of Chemistry 2011