A new strategy for catalytic Baeyer-Villiger oxidation of KA-oil with molecular oxygen using N-hydroxyphthalimide

Article abstract of DOI:10.1016/S0040-4039(01)00469-5

Catalytic Baeyer-Villiger oxidation of KA-oil (a mixture of cyclohexanone and cyclohexanol) with molecular oxygen has been developed. The oxidation of KA-oil under dioxygen atmosphere in the presence of a catalytic amount of N-hydroxyphthalimide followed by treatment with indium trichloride gave ε-caprolactone.

Full text of DOI:10.1016/S0040-4039(01)00469-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 3479–3481
A new strategy for catalytic Baeyer–Villiger oxidation of KA-oil
with molecular oxygen using N-hydroxyphthalimide
Osamu Fukuda, Satoshi Sakaguchi and Yasutaka Ishii*
Department of Applied Chemistry, Faculty of Engineering & High Technology Research Center, Kansai University, Suita,
Osaka 564-8680, Japan
Received 14 March 2001; revised 16 March 2001; accepted 21 March 2001
Abstract—Catalytic Baeyer–Villiger oxidation of KA-oil (a mixture of cyclohexanone and cyclohexanol) with molecular oxygen
has been developed. The oxidation of KA-oil under dioxygen atmosphere in the presence of a catalytic amount of N-hydroxyph-
thalimide followed by treatment with indium trichloride gave o-caprolactone. © 2001 Elsevier Science Ltd. All rights reserved.
KA-oil, a mixture of cyclohexanone and cyclohexanol
obtained by the aerobic oxidation of cyclohexane, is an
important intermediate in the petroleum industrial
chemistry for the production of adipic acid and o-
caprolactam which are key materials for manufacturing
6,6-nylon and 6-nylon, respectively.1
In previous work, we have shown that N-hydroxyph-
thalimide (NHPI) acts as an efficient catalyst for the
aerobic oxidation of various organic substrates.6 The
NHPI-catalyzed oxidation of secondary alcohols gave
ketones through the formation of a-hydroxyhydroper-
oxide as an intermediate.7 From both synthetic and
industrial points of view, it is very attractive that the
KA-oil can be used as the starting material for the
production of o-caprolactone with molecular oxygen
via a catalytic process. In this paper, we wish to report
a new Baeyer–Villiger oxidation of KA-oil with molec-
ular oxygen under the influence of the NHPI catalyst.
To our best knowledge, there are no reports on the
catalytic Baeyer–Villiger oxidation of KA-oil using
dioxygen as the terminal oxidant.
Baeyer–Villiger oxidation is a frequently used synthetic
tool for conversion of cycloalkanones to lactones. Usu-
ally, this transformation is carried out by the use of
peracids like peracetic acid and mCPBA,2 hydrogen
peroxide,3 and bis(trimethylsilyl)peroxide.4 However,
the catalytic Baeyer–Villiger oxidation using dioxygen
is limited to the in situ generation of peracids using
excess aldehydes and O2.5 In industry, o-caprolactone is
manufactured by the reaction of cyclohexanone with
peracetic acid generated by the aerobic oxidation of
acetaldehyde.1
Our strategy is outlined in Scheme 1. The aerobic
oxidation of cyclohexanol (2) catalyzed by NHPI gives
O
cat.
O
O
OH
NOH
O
HO
OOH
O
O
catalyst
O2
+
+
+
1
2
A
3
path 1
path 2
O
H2O2
+
2
Scheme 1.
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00469-5

3480
O. Fukuda et al. / Tetrahedron Letters 42 (2001) 3479–3481
a mixture of cyclohexanone (1) and hydrogen peroxide
through the formation of 1-hydroxy-1-hydroperoxycy-
clohexane (A) (path 1). Treatment of the resulting
reaction mixture with an appropriate catalyst would
produce o-caprolactone (3) (path 2). A KA-oil consist-
ing of a 1:1 mixture of 1 and 2 was employed as a
model starting material. If the aerobic oxidation of the
KA-oil in the presence of NHPI is completed, 2 equiv.
of 1 and 1 equiv. of H2O2 are expected to be formed.
without treatment with InCl3 (run 3). Without treat-
ment of the reaction mixture with PPh3, the amount of
KA-oil recovered was slightly lowered, because of the
presence of unreacted hydroperoxides which are even-
tually converted into 1 and 2 upon treatment with PPh3
(run 4). Indeed, the addition of a KI solution to the
reaction mixture before treatment with PPh3 led to
color change from light yellow to red–brown, which
indicates the presence of peroxy compounds.
1) cat. NHPI
2) cat. InCl3
25 oC, 6 h
AIBN
(1)
+
+
O2
1
2
3
CH3CN,
75 oC, 15 h
(1 atm)
A standard experimental procedure is as follows: To a
solution of NHPI (0.6 mmol) and 2,2%-azobisisobutyro-
nitrile (AIBN) (0.3 mmol) in CH3CN (3 mL) was added
a 1:1 mixture of 1 (6 mmol) and 2 (6 mmol), and then
the flask was flushed with dioxygen and equipped with
a balloon filled with about 2 L of O2. After stirring the
reaction mixture at 75°C for 15 h, InCl3 (0.45 mmol)
was added and further stirred at 25°C for 6 h. To
decompose the unreacted peroxides, the reaction mix-
ture was treated with excess PPh3 (10 mmol) at room
temperature for several hours. The yields of products
were estimated from the peak areas based on the inter-
nal standard technique using GC.
Water-stable Lewis acids such as Sc(OTf)3 and
Gd(OTf)3 were also effective to give 3 in somewhat
lower yields (runs 5 and 6). When a protic acid like
sulfuric acid was used instead of Lewis acids, peroxy
compounds, 4a and 4b, derived from 2 and H2O2 were
formed as major products. It is well-known that 1
reacts with aqueous hydrogen peroxide under neutral
and acidic conditions to produce 4a and 4b,
respectively.3a,9
The oxidation of 2 to 1 was enhanced by the use of the
NHPI–Co(II) system,10 but the formation of 3 was
markedly inhibited by the Co ion (run 7). This is
believed to be due to the rapid decomposition of the
resulting hydroperoixde A as well as H2O2 by the Co
ion, since hydroperoxides undergo the redox decompo-
sition by transition metals.11 The commercially avail-
able KA-oil consists of a 1:2.5–4 mixture of 1 and 2,1
therefore we examined the oxidation of a 1:2 mixture of
1 and 2. The reaction under these reaction conditions
Table 1 summarizes the representative results for the
Baeyer–Villiger oxidation of the KA-oil. The reaction
under standard conditions gave o-caprolactone (3) in
57% selectivity based on the KA-oil reacted,8 and 77%
of KA-oil was recovered (Eq. (1), run 1). This reaction
is the first catalytic Baeyer–Villiger reaction of KA-oil
with molecular oxygen. The KA-oil recovered includes
cyclohexanone 1 as the main component. The same
oxidation in the absence of AIBN gave 3 (0.9 mmol)
(run 2). Compound 3 was formed in very low yield
O O
O O
4a
4b
O O
H H
O O
H OH
Table 1. Baeyer–Villiger oxidation of KA-oil with molecular oxygen under various conditionsa
Run
Catalyst
Yield of 3 (mmol)
Selectivity of 3 (%)b
Recovery of KA-oil (%)
1/2 (mmol/mmol)
1
InCl3
InCl3
–
InCl3
Sc(OTf)3
Gd(OTf)3
InCl3
InCl3
InCl3
1.6
0.9
0.4
1.6
0.7
1.4
B1
1.6
57
60
19
36
18
40
B1
57
77
88
83
63
67
70
91
69
79
(8.0/1.2)
(6.9/3.6)
(8.9/1.0)
(6.8/0.8)
(7.1/0.9)
(7.4/1.0)
(10.9/0.1)
(4.9/1.3)
(8.0/1.5)
2c
3
4d
5
6
7e
8f
9g
1.5
60
a Reaction conditions are shown in text.
b See Ref. 8.
c Without AIBN.
d Without treatment of the reaction mixture with PPh3.
e Co(OAc)2 (0.03 mmol) was added in the step of the aerobic oxidation of KA-oil.
f A 1:2 mixture of 1 (3 mmol) and 2 (6 mmol) was used.
g 0.9 mmol of InCl3 was used.

O. Fukuda et al. / Tetrahedron Letters 42 (2001) 3479–3481
3481
1) cat. NHPI
2) cat. InCl3
AIBN
+
+
3
1
2
+
O2
2
CH3CN,
25 oC, 6 h
(2)
75 oC, 15 h
(6 mmol)
(1 atm)
(1.5 mmol) (2.8 mmol) (0.9 mmol)
was found to afford 3 in almost the same yield and
selectivity as run 1 (run 8). As expected, similar treat-
ment of cyclohexanol 2 alone with that of the KA-oil
led to o-caprolactone 3 and cyclohexanone 1. The aero-
bic oxidation of 2 under the influence of the NHPI
catalyst followed by treatment with InCl3 and then
PPh3 afforded 3 (1.5 mmol) and 1 (2.8 mmol) (Eq. (2)).
1999, 180, 435–443; (b) Strukul, G.; Varagnolo, A.;
Pinna, F. J. Mol. Catal. A: Chem. 1997, 117, 413–423; (c)
Wang, Z. B.; Mizusaki, T.; Sano, T.; Kawakami, Y. Bull.
Chem. Soc. Jpn. 1997, 70, 25967–25970; (d) Frisone, M.;
Del, T.; Pinna, F.; Strukul, G. Organometallics 1993, 12,
148–156.
4. Go¨ttlich, R.; Yamakoshi, K.; Sasai, H.; Shibasaki, M.
Synlett 1997, 971–973.
In conclusion, a catalytic Baeyer–Villiger oxidation of
KA-oil with molecular oxygen has first been developed
by the use of NHPI as a catalyst. Although the
efficiency of the reaction must be improved and more
efficient and cheaper catalyst than InCl3 should be
developed, this method may provide an ideal strategy
for the production of o-caprolactone 3 from a KA-oil
which is a raw material manufactured largely by the
aerobic oxidation of cyclohexane.
5. (a) Bolm, A.; Schlingloff, G.; Weickhardt, K. Tetra-
hedron Lett. 1993, 34, 3405–3408; (b) Hamamoto, M.;
Nakayama, K.; Nishiyama, Y.; Ishii, Y. J. Org. Chem.
1993, 58, 6421–6425; (c) Murahashi, S.; Oda, Y.; Naota,
T. Tetrahedron Lett. 1992, 33, 7557–7560; (d) Yamada,
T.; Takahashi, K.; Kato, K.; Takai, T.; Inoki, S.;
Mukaiyama, T. Chem. Lett. 1991, 641–644.
6. (a) Sakaguchi, S.; Takase, T.; Iwahama, T.; Ishii, Y.
Chem. Commun. 1998, 2037–2038; (b) Sakaguchi, S.;
Kato, S.; Iwahama, T.; Ishii, Y. Bull. Chem. Soc. Jpn.
1998, 71, 1237–1240; (c) Yoshino, Y.; Hayashi, Y.; Iwa-
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Acknowledgements
This work was partly supported by Research for the
Future program JSPS.
8. The selectivity (%) of 3 was calculated by the following
equation.
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