Dirhodium(II) carboxylate-catalysed oxidation of allylic and benzylic alcohols

Article abstract of DOI:10.1016/S0040-4039(01)02048-2

Allylic and benzylic alcohols are oxidised to the corresponding carbonyl compounds using tert-butyl hydroperoxide, preferably in stoichiometric amounts, and dirhodium(II) tetraacetate as catalyst (1 mol%) in dichloromethane at ambient temperature.

Full text of DOI:10.1016/S0040-4039(01)02048-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 139–141
Dirhodium(II) carboxylate-catalysed oxidation of allylic and
benzylic alcohols
Christopher J. Moody* and Francine N. Palmer
School of Chemistry, University of Exeter, Stocker Road, Exeter EX4 4QD, UK
Received 20 September 2001; accepted 26 October 2001
Abstract—Allylic and benzylic alcohols are oxidised to the corresponding carbonyl compounds using tert-butyl hydroperoxide,
preferably in stoichiometric amounts, and dirhodium(II) tetraacetate as catalyst (1 mol%) in dichloromethane at ambient
temperature. © 2001 Elsevier Science Ltd. All rights reserved.
The oxidation of alcohols to the corresponding car-
bonyl compound is a transformation that is fundamen-
tal to synthetic organic chemistry, and numerous
reagents, many of them metal based, have been devel-
was faster under O2 than air, it was only ca. 40%
20
complete even after 120 h, by which time it appeared
that the catalyst was no longer active (colour change to
yellow). Changing to a catalyst with more strongly
electron-withdrawing carboxylate ligands, such as
Rh (OCOCF ) or Rh (OCOC F ) , resulted in a longer
1
oped to carry out this important reaction. However,
with the increasing emphasis on protocols that are
acceptable from the economic and ecological point of
view, recent efforts have focused on systems which
employ metals only in catalytic amounts together with
an inexpensive stoichiometric oxidant such as a perox-
ide, molecular oxygen or, ideally, air. Recent examples
2
3 4
2
3 7 4
lived catalytic species (>3 weeks). However, the rate of
oxidation of 2-cyclohexenol was slower than with
Rh (OAc) itself, and using Rh (OCOCF ) as catalyst,
2
4
2
3 4
2
2
-cyclohexenone was formed in ca. 55% yield only after
0 days. Therefore, in order to decrease the inconve-
2
,3
include systems based on ruthenium [Ru(II),
niently long reaction times, the amount of oxidant was
increased; with 100 mol% oxidant and 1 mol%
Rh (OAc) , the oxidation was >85% complete after 24
4
,5
6–8
9–11
Ru(III), or perruthenate ], copper,
and palladium-
Much less common is the use of
rhodium based catalysts, despite the fact that they
have long been known to catalyse such processes as
1
2–14
(
II) acetate.
15
2
4
h.
1
6–18
allylic oxidation.
In view of our interest in dirhod-
Having established useful reaction conditions, the
method was applied to other alcohols. The results,
which are shown in Table 1, show that the method is
generally applicable to a range of secondary allylic and
benzylic alcohols, and gives the corresponding ketones
in good yield. Most of the oxidations are complete
within 24–30 h, although 1-phenylethanol and 1-
phenyl-butanol are oxidised more slowly.
ium(II)-catalysed processes in organic synthesis, we ini-
tiated a study into the use of dirhodium(II) carboxy-
19
lates as catalysts for oxidation reactions. We now
report that allylic and benzylic alcohols are readily
oxidised to the corresponding carbonyl compounds
using tert-butyl hydroperoxide (TBHP) in the presence
of catalytic amounts of dirhodium(II) tetracarboxyl-
ates.
Primary allylic and benzylic alcohols are also oxidised
under the reaction conditions, although the yields of
the corresponding aldehydes (25–45% by GC) are con-
siderably lower, due to by-product formation. Unacti-
vated primary and secondary alcohols such as
2-hexanol or cyclohexanol were not efficiently oxidised
under the above conditions.
When a dichloromethane solution of 2-cyclohexenol
was stirred with tert-butyl hydroperoxide (ca. 1 mol%)
and Rh (OAc) (1 mol%) either open to the air or
under an oxygen atmosphere, slow oxidation to 2-
cyclohexenone occurred. No significant oxidation
occurs in the absence of the rhodium complex.
Although the reaction, which was monitored by GC,
2
4
In summary dirhodium(II) tetraacetate is an efficient
catalyst for the oxidation of secondary allylic and ben-
*
0
Corresponding author.
040-4039/02/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02048-2

1
40
C. J. Moody, F. N. Palmer / Tetrahedron Letters 43 (2002) 139–141
a
Table 1. Oxidation of secondary allylic and benzylic alcohols catalysed by Rh (OAc) using TBHP
2
4
a
Reaction conditions: CAUTION: all mixtures involving peroxides should be handled using appropriate precautions. A solution of alcohol (ca.
.0 g), and TBHP (100 mol%, 5–6 M in decane) in dichloromethane (0.1 M) was added to a sealed vessel containing Rh (OAc) (1 mol%), which
1
2
4
had been twice evacuated and flushed with O . The reaction mixture was stirred under an O atmosphere at room temperature for the time
2
2
indicated.
b
c
Yields were determined by GC analysis using an internal standard technique.
Thin layer chromatography was employed to follow reaction progression; only preparative scale reactions were performed.
d
e
4
5% of the starting 1-phenylethanol was recovered from column chromatography.
5
5% of the starting 1-phenylbutanol was recovered from column chromatography.
zylic alcohols using tert-butyl hydroperoxide as
oxidant.
References
1
. Smith, M. B.; March, J. In March’s Advanced Organic
Chemistry; 5th ed., Wiley-Interscience: New York, 2001,
Chapter 19.
Acknowledgements
We thank the EPSRC for their support of this work,
and Dr. J. L. O’Connell for preliminary experiments.
2. Lee, M.; Chang, S. B. Tetrahedron Lett. 2000, 41, 7507–
7510.

C. J. Moody, F. N. Palmer / Tetrahedron Letters 43 (2002) 139–141
. Che, C. M.; Cheng, K. W.; Chan, M. C. W.; Lau, T. C.; Chem. 2001, 624, 344–347.
141
3
4
5
6
7
Mak, C. K. J. Org. Chem. 2000, 65, 7996–8000.
. Fung, W. H.; Yu, W. Y.; Che, C. M. J. Org. Chem. 1998,
12. Peterson, K. P.; Larock, R. C. J. Org. Chem. 1998, 63,
3185–3189.
6
3, 2873–2877.
13. Nishimura, T.; Onoue, T.; Ohe, K.; Uemura, S. J. Org.
Chem. 1999, 64, 6750–6755.
. Yamaguchi, K.; Mori, K.; Mizugaki, T.; Ebitani, K.;
Kaneda, K. J. Am. Chem. Soc. 2000, 122, 7144–7145.
. Lenz, R.; Ley, S. V. J. Chem. Soc., Perkin Trans. 1 1997,
1
1
1
4. Nishimura, T.; Maeda, Y.; Kakiuchi, N.; Uemura, S. J.
Chem. Soc., Perkin Trans. 1 2000, 4301–4305.
5. For example: Kolle, U.; Franzl, H. Monatsh. Chem. 2000,
3
291–3292.
. Marko, I. E.; Giles, P. R.; Tsukazaki, M.; Chelle-Reg-
naut, I.; Urch, C. J.; Brown, S. M. J. Am. Chem. Soc.
131, 1321–1326.
6. Noels, A. F.; Hubert, A. J.; Teyssi e´ , P. J. Organomet.
Chem. 1979, 166, 79–86.
1
997, 119, 12661–12662.
8
. Marko, I. E.; Gautier, A.; Tsukazaki, M.; Llobet, A.;
Plantalech-Mir, E.; Urch, C. J.; Brown, S. M. Angew.
Chem., Int. Ed. 1999, 38, 1960–1962.
. Marko, I. E.; Giles, P. R.; Tsukazaki, M.; Chelle-Reg-
naut, I.; Gautier, A.; Brown, S. M.; Urch, C. J. J. Org.
Chem. 1999, 64, 2433–2439.
0. Kitagaki, S.; Yasugahira, M.; Anada, M.; Nakajima, M.;
Hashimoto, S. Tetrahedron Lett. 2000, 41, 5931–5935.
1. Marko, I. E.; Gautier, A.; Mutonkole, J. L.; Dumeunier,
R.; Ates, A.; Urch, C. J.; Brown, S. M. J. Organomet.
1
1
7. Uemura, S.; Patil, S. R. Chem. Lett. 1982, 1743–1746.
8. Doyle, M. P.; Terpstra, J. W.; Winter, C. H.; Griffen, J.
H. J. Mol. Cat. 1984, 26, 259–266.
9
1
9. Dirhodium(II) tetraacetate has been reported to be a
catalyst, albeit an inefficient one, in the oxidation of
ethanol to acetaldehyde with air: Bibby, C. E.; Grigg, R.;
Price, R. J. Chem. Soc., Dalton Trans. 1977, 872–876.
0. Two minor products which derive by further oxidation of
the product were also observed.
1
2
1
.