4
Tetrahedron
oxidation reaction. Under argon atmosphere, the control
Acknowledgments
experiments demonstrably revealed that Cu(OAc)2 regenerated
active TEMPO (entry 10), meantime, Cu(OAc)2, comparing to
other copper salts, could be more efficiently renovated via the
air-sensitive CuOAc (entry 11).[15]
The authors are grateful to the National Natural Science
Foundation of China (Project No. 21176074) for financial
support.
Table 3. Control experiments for the aerobic oxidation of benzyl alcohol.a
Supplementary Date
Supplementary data associated with this article can be found,
in the online version, at ……
Entry Cu salt (n1 mol%) TEMPO (n2 mol%) Atmos.
Yieldb (%)
References and notes
1
Cu(OAc)2 (1)
CuCl2 (1)
1
air
92
air
2
1
39
1. Caron, S.; Dugger, R. W.; Ruggeri, S. G.; Ragan, J. A.; Ripin, D.
H. B. Chem. Rev. 2006, 106, 2943.
3
CuCl (1)
1
air
23
2. Tojo, G.; Fernandez, M. I. (Eds.), Oxidation of Alcohols to
Aldehydes and Ketones: A Guide to Current Common Practice,
Springer, Berlin, Heidelberg, 2006.
3. For representative reports, see: (a) Peterson, K. P.; Larock, R. C.;
J. Org. Chem. 1998, 63, 3185; (b) Brink, G. T.; Arends, I. W. C.
E.; Sheldon, R. A. Science 2000, 287, 1636; (c) Jensen, D. R.;
Schultz, M. J.; Mueller, J. A.; Sigman, M. S. Angew. Chem. Int.
Ed. 2003, 42, 3810; (d) Sigman, M. S.; Jensen, D. R. Acc. Chem.
Rec. 2006, 39, 221.
4. For representative reports, see: (a) Dijksman, A.; Arends, I. W. C.
E.; Sheldon, R. A. Chem. Commun. 1999, 1591; (b) Yamaguchi,
K.; Mizuno, N. Angew. Chem. Int. Ed. 2002, 41, 4538; (c)
Takahashi, M.; Oshima, K.; Matsubara, S. Tetrahedron Lett. 2003,
44, 9201; (d) Das, P.; Aggarwal, N.; Guha, N. R. Tetrahedron Lett.
2013, 54, 2924.
4
Cu(OTf)2 (1)
CuOTf (1)
1
air
56
5
1
air
66
6c
7d
8
Cu(OAc)2 (1)
Cu(OAc)2 (1)
Cu(OAc)2 (200)
none
1
air
92
1
air
trace
0
none
200
1
air
9
air
92
10
11
Cu(OAc)2 (200)
Cu(OAc)2 (1)
argon
argon
94
1
trace
a The reaction performed with benzyl alcohol (0.54 g, 5.0 mmol), Cu(OAc)2
(n1 mol%) and TEMPO (n2 mol%) in CH3CN/H2O (5 mL/10 mL) under
ambient temperature and specified atmos. (1.0 atm) for 3 h. b Isolated yield
c
d
via column chromatography. AcOH (0.03 g, 0.5 mmol) added. Na2CO3
(0.05 g, 0.5 mmol) added.
5. Iwahama, T.; Sakaguchi, S.; Nishiyama, Y.; Ishii, Y. Tetrahedron
Based on the above experiments and the reported TEMPO
Lett. 1995, 36, 6923.
6. Lorber, C. Y.; Smidt, S. P.; Osborn, J. A. Eur. J. Inorg. Chem.
2000, 655.
catalytic systems,[14a,14c,14e,14g]
a catalytic sequence for the
oxidation was proposed in Scheme 1. Initially, TEMPO is
disproportionated into TEMPOH and the oxo-ammonium ion in
our reaction conditions (Eq. 1). Then, the oxo-ammonium ion
acts as a well-known oxidant[14a,14c,14e,14g] to oxidize alcohols into
the corresponding carbonyl compounds with TEMPOH released
(Eq. 2). Furthermore, Cu(OAc)2 as a redox-active cocatalyst
reoxidize TEMPOH into TEMPO (Eq. 3). Lastly, oxygen in air as
the terminal oxidant renovates Cu(OAc)2 by an oxidation process
(Eq. 4).[15]
7. Jia, C. G.; Jing, F. Y.; Hu, W. D.; Huang, M. Y.; Jiang, Y. Y. J.
Mol. Catal. 1994, 91, 139.
8. Dobler, C.; Mehltretter, G. M.; Sundermeier, U.; Eckert, M.;
Militzer, H. C.; Beller, M. Tetrahedron Lett. 2001, 42, 8447.
9. Choudary, B. M.; Kantam, M. L.; Rahman, A.; Reddy, C. V.; Rao,
K. K. Angew. Chem. Int. Ed. 2001, 40, 763.
10. For representative reports, see: (a) Higuchi, M.; Ikeda, I.; Hirao, T.
J. Org. Chem. 1997, 62, 1072; (b) Martin, S. E.; Suarez, D. F.
Tetrahedron Lett. 2002, 43, 4475; (c) Wang, N.; Liu, R.; Chen, J.;
Liang, X. Chem. Commun. 2005, 5322; (d) Namboodiri, V. V.;
Polshettiwar, V.; Varma, R. S. Tetrahedron Lett. 2007, 48, 8839;
(e) Yin, W.; Chu, C.; Lu, Q.; Tao, J.; Liang, X.; Liu, R. Adv. Synth.
Catal. 2010, 352, 113; (f) Ma, S.; Liu, J.; Li, S.; Chen, B.; Cheng,
J.; Kuang, J.; Liu, Y.; Wan, B.; Wang, Y.; Ye, J.; Yu, Q.; Yuan,
W.; Yu, S. Adv. Synth. Catal. 2011, 353, 1005.
11. For representative reports, see: (a) Marko, I. E.; Giles, P. R.;
Tsukazaki, M.; Brown, S. M.; Urch, C. J. Science 1996, 274, 2044;
(b) Gamez, P.; Arends, I. W. C. E.; Reedijk, J.; Sheldon, R. A.
Chem. Commun. 2003, 2414; (c) Marko, I. E.; Gautier, A.;
Dumeunier, R.; Doda, K.; Philippart, F.; Brown, S. M.; Urch, C. J.
Angew. Chem. Int. Ed. 2004, 43, 1588; (d) Mase, N.; Mizumori, T.;
Tatemoto, Y. Chem. Commun. 2011, 47, 2086; (e) Hoover, J. M.;
Stahl, S. S. J. Am. Chem. Soc. 2011, 133, 16901.
12. For a recent comprehensive review, see: Piera, J.; Backvall, J.-E.
Scheme 1. A proposed mechanism.
Angew. Chem. Int. Ed. 2008, 47, 3506.
13. For representative reports, see: (a) Sheldon, R. A.; Arends, I. W. C.
E. Adv. Synth. Catal. 2004, 346, 1051; (b) Karimi, B.; Biglari, A.;
Clark, J. H.; Budarin, V. Angew. Chem. Int. Ed. 2007, 46, 7210; (c)
Wang, X.; Liu, R.; Jin, Y.; Liang, X. Chem. Eur. J. 2008, 14, 2679.
14. For transition metal assisted TEMPO-catalyzed aerobic alcohol
oxidations, see, (a) Semmelhack, M. F.; Schmidt, C. R.; Cortes, D.
A.; Chou, C. S. J. Am. Chem. Soc. 1984, 106, 3374; (b)
Betzemeier, B.; Cavazzini, M.; Quici, S.; Knochel, P. Tetrahedron
Lett. 2000, 41, 4343; (c) Cecchetto, A.; Fontana, F.; Minisci, F.;
Recupero, F. Tetrahedron Lett. 2001, 42, 6651; (d) Dijksman, A.;
Marino-Gonzalez, A.; Payeras, A. M.; Arends, I. W. C. E.;
Sheldon, R. A. J. Am. Chem. Soc. 2001, 123, 6826; (e) Ben-Daniel,
R.; Alsters, P.; Neumann, R. J. Org. Chem. 2001, 66, 8650; (f)
Ansari, I. A.; Gree, R. Org. Lett. 2002, 4, 1507; (g) Minisci, F.;
Recupero, F.; Cecchetto, A.; Gambarotti, C.; Punta, C.; Faletti, R.;
Paganelli, R.; Pedulli, G. F. Eur. J. Org. Chem. 2004, 109; (h)
Jiang, N,; Ragauskas, A. J. Org. Lett. 2005, 7, 3689; (i) Shibuya,
In conclusion, we have developed a practical ligand- and
additive-free Cu(OAc)2/TEMPO catalyst system for aerobic
alcohol oxidation. Under ambient conditions, a wide range of
primary and second benzylic alcohols, primary and secondary 1-
heteroaryl alcohols, cinnamyl alcohols and aliphatic alcohols
were selectively transformed into the corresponding aldehydes
and ketones in good to excellent yields with low catalyst loading.
Furthermore, a plausible reaction mechanism was proposed based
on experimental observations and literatures. In terms of both
economical and environmental considerations, we believed that
the oxidation protocol holds a potential value in laboratory and
industry.