Wacker-type oxidation of cyclopentene under dioxygen atmosphere catalyzed by Pd(OAc)2/NPMoV on activated carbon

Article abstract of DOI:10.1016/S0040-4039(99)02012-2

Wacker-type oxidation of cyclopentene to cyclopentanone under dioxygen atmosphere was successfully achieved by the use of Pd(OAc)₂ and molybdovanadophosphate supported on activated carbon, [Pd(OAc)₂-NPMoV/C], catalyst. Thus, the reaction of cyclopentene under O₂ (1 atm) in aqueous acetonitrile acidified by CH₃SO₃H in the presence of [Pd(OAc)₂-NPMoV/C] at 50°C produced cyclopentanone in 85% yield along with a small amount of cyclopentenone (1%).

Full text of DOI:10.1016/S0040-4039(99)02012-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 99–102
Wacker-type oxidation of cyclopentene under dioxygen
atmosphere catalyzed by Pd(OAc)2/NPMoV on activated carbon
Arata Kishi, Takashi Higashino, Satoshi Sakaguchi and Yasutaka Ishii ∗
Department of Applied Chemistry, Faculty of Engineering & High Technology Research Center, Kansai University Suita,
Osaka 564-8680, Japan
Received 16 September 1999; revised 18 October 1999; accepted 22 October 1999
Abstract
Wacker-type oxidation of cyclopentene to cyclopentanone under dioxygen atmosphere was successfully achiev-
ed by the use of Pd(OAc)2 and molybdovanadophosphate supported on activated carbon, [Pd(OAc)2–NPMoV/C],
catalyst. Thus, the reaction of cyclopentene under O2 (1 atm) in aqueous acetonitrile acidified by CH3SO3H in the
presence of [Pd(OAc)2–NPMoV/C] at 50°C produced cyclopentanone in 85% yield along with a small amount of
cyclopentenone (1%). © 1999 Elsevier Science Ltd. All rights reserved.
The oxidation of terminal alkenes by the Wacker system consisting of PdCl2/CuCl2/O2 to form the
corresponding ketones is a well-established method and a very important process in both synthetic
and industrial chemistry.1 However, this catalytic system has disadvantages caused by the chlorine
anion which leads to the formation of chlorinated by-products and corrodes the reactor, and it is
not suitable for oxidation of higher olefins and cycloalkenes.2 For this reason much effort has been
devoted to the development of aerobic oxidation of cycloalkenes using chloride-free oxidizing systems.3
Heteropolyacids have frequently been used as the reoxidation catalyst of the reduced Pd(0) to Pd(II) in
place of CuCl2.4
Cyclopentanone (CPO) is an important starting material for the synthesis of a variety of pharma-
ceuticals and perfumes involving a cyclopentanone framework as exemplified by jasmonates. Although
there have been several reports on the synthesis of CPO from cyclopentene (CP) by the Wacker system,5
CPO is currently manufactured by the Dieckmann condensation of adipic acid. Therefore, if CPO can be
produced by a chloride-free Wacker-type oxidation of CP, this method would provide a very useful means
for the synthesis of CPO, because CP is easily obtained by partial hydrogenation of cyclopentadiene
which is a very cheap compound and easily available from the petroleum industry.
∗
Corresponding author.
0040-4039/00/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(99)02012-2
tetl 15940

100
(1)
We would like to report here heterogeneous Wacker-type oxidation of CP to CPO by Pd(II) and
molybdovanadophosphate (NPMoV) supported on acivated carbon (hereafter abbreviated to Pd(II)–
NPMoV/C)6 using molecular oxygen as the terminal oxidant (Eq. (1)).
A typical reaction was carried out as follows: To a suspended solution of [10 wt%Pd(OAc)2−
15 wt%NPMoV/C] (100 mg) was added CP (2 mmol) and CH3SO3H (20 mg), and the mixture was stirred
under dioxygen atmosphere (1 atm) at 50°C for 6 h (standard conditions). Products were isolated by
column chromatography on silica gel with hexane:ethyl acetate (10:1) eluent.
Table 1 shows the representative results for the oxidation of CP to CPO by [10 wt%Pd(OAc)2−
15wt%NPMoV/C] under various conditions. The oxidation of CP by [10 wt%Pd(OAc)2−15wt%NPMoV/C]
in acidic CH3CN/H2O under the standard conditions afforded CPO in 85% yield along with a small
amount of cyclopentenone (CPEO) (1%) (run 1). The oxidation was markedly affected by the acid-
Table 1
Oxidation of cyclopentene (CP) to cyclopentanone (CPO) and cyclopentenone (CPEO) under various
reaction conditionsa)

101
ity of the reaction medium. Although p-toluenesulfonic acid had the same effect as CH3SO3H, the
reaction in the absence of acid resulted in no formation of CPO (runs 2 and 3). Similar rate en-
hancement by the addition of acid is reported by several authors.8 In a previous paper, we sho-
wed that the aerobic oxidation of benzyl alcohols by NPMoV/C is facilitated by adding an acid,
and that the reoxidation of the reduced [NPMoV]red. to the original oxidation state of NPMoV pro-
ceeds smoothly under acidic conditions.9 Thus, CP was converted into CPO in satisfactory yield
in acidic CH3CN/H2O under the influence of [10 wt%Pd(OAc)2−15 wt%NPMoV/C]. Among the acti-
vated carbons used, Kurare BP-25 was the best support (runs 4 to 6). Pd(OAc)2–NPMoV suppor-
ted on activated carbon having large surface area showed higher activity. We believe that dioxy-
gen adsorbed on the activated carbon promotes smooth reoxidation of reduced [NPMoV]red. to NP-
MoV which oxidizes Pd(0) to Pd(II). Several Pd(II) catalysts, [10 wt%Pd(SO4)2−15 wt%NPMoV/C] and
[
10 wt%PdCl2−15 wt%NPMoV/C] which were loaded on the Kurare BP-25 were prepared, and the ac-
tivity of these catalysts was compared with that of the [10 wt%Pd(OAc)2−15 wt%NPMoV/C] (runs 7
and 8). The order of the activity of catalysts was as follows: [10 wt%Pd(OAc)2−15 wt%NPMoV/C],
[
10 wt%PdCl2−15 wt%NPMoV/C] and then [10 wt%Pd(SO4)2−15 wt%NPMoV/C]. It is interesting that the
activity of [10 wt%Pd(OAc)2−15wt%NPMoV/C] is higher than that of non-supported Pd(OAc)2 combined
with NPMoV which gave CPO (75%) and CPEO (1%) (run 9). The benefit of the use of heterogeneous
[
10 wt%Pd(OAc)2−15 wt%NPMoV/C] is that the catalyst can be easily recovered by filtration from the
reaction mixture. The oxidation of CP by the recovered [10 wt%Pd(OAc)2−15 wt%NPMoV/C] catalyst
from aqueous CH3CN resulted in CPO in lower yield than that by the fresh catalyst (run 10). From
the ICP analysis, it was found that the deactivation of the catalyst is attributed to the leaching of metal
ions (Pd=9.03×10−3 mmol (41%), Mo=0.16×10−3 mmol (1%), V=8.64×10−3 mmol (26%)) from the
[
10 wt%Pd(OAc)2−15 wt%NPMoV/C] catalyst to the aqueous CH3CN. Although the oxidation of CP by
fresh [10 wt%Pd(OAc)2−15 wt%NPMoV/C] in EtOH/H2O led to CPO in slightly lower yield than that in
CH3CN/H2O (run 11), it was found that the leaching of the Pd ion from the catalyst was markedly
suppressed. The quantity of leaching of metal ions to aqueous EtOH was as follows: Pd=0.25×10−3
mmol (1%), Mo=0.21×10−3 mmol (1%), V=6.15×10−3 mmol (18%). Therefore, when NPMoV was
added to the recovered catalyst from the EtOH/H2O, CPO was obtained in high yield (run 13). This
indicates that the added NPMoV can reoxidize the Pd(0) species to a Pd(II) species. Thus, the oxidation
by [10 wt%Pd(OAc)2/C] catalyst in the presence of NPMoV was examined in EtOH/H2O at 50°C for 2
h, and CPO was obtained in high yield (90%) together with CPEO (4%) (run 15). Table 2 shows the
oxidation of CP by [10 wt%Pd(OAc)2/C] (100 mg) and its recovered catalyst combined with NPMoV. It
is interesting to note that the catalytic activity of [10 wt%Pd(OAc)2/C] was maintained after using three
times.
Table 2
Oxidation of CP by the recovered catalysta)

102
In conclusion, Wacker-type oxidation of CP to CPO using O2 as terminal oxidant was successfully
achieved by using a chloride-free reoxidation system under mild conditions. This method provides an
alternative useful direct route for the production of CPO from CP easily derived from dicyclopentadiene
which is formed in large quantity in the petroleum refining process.
Acknowledgements
This work was financially supported by Grant-in-Aid for Scientific Research (No. 10450337) from the
Ministry of Education, Science and Culture, Japan.
References
1. (a) Tsuji, J. Palladium Reagents and Catalysts Innovations in Organic Synthesis; John Wiley & Sons: New York, 1998.
(b) Metal-Catalyzed Cross-Coupling Reactions; Diederich, F.; Stang, P. J., Eds.; John Wiley & Sons: New York, 1998; pp.
339–453.
2. Tsuji, J. Synthesis 1990, 9, 739–749.
3. Tsuji, J.; Minato, M. Tetrahedron Lett. 1987, 28, 3683–3686.
4. (a) Matveev, K. I. Kinet. Katal. 1977, 18, 862–877. (b) Catalysis in Organic Reactions; Grate, G. H.; Kosak, J. R.; Johnson,
T. A., Eds.; Dekker: New York, 1994; p. 213. (c) Ogawa, H.; Fujinami, H.; Taya, K.; Teratani, S. Bull. Chem. Soc. Jpn. 1984,
57, 1908–1913. (d) Ogawa, H.; Fujinami, H.; Taya, K. J. Chem. Soc., Chem. Commun. 1981, 1274–1275.
5. (a) Takehira, K.; Hayakawa, T.; Orita, H.; Shimizu, M. J. Mol. Catal. 1989, 53, 15–21. (b) Takehira, K.; Hayakawa, T.; Orita,
H.; Shimizu, M. J. Mol. Catal. 1989, 53, 105–109.
6. Activated carbons available from commercial source: Kurare BP-25 (2420 cm2/g), Kurare coal GLC (1570 cm2/g),
Shirasagi (1200 cm2/g) and Darco (650 cm2/g). Molybdovanadophosphate (NPMoV) was prepared according to the literature
procedure.7a To a solution of NaVO3 (7.32 g, 60 mmol) in water (38 mL) was added Na2MoO4·2H2O (18.22 g, 34 mmol) in
water (12 mL). To the resulting solution was added 85˝
3PO4 (7.6 g, 66 mmol) in water (10 mL) and the mixture was heated to 95°C under stirring for 1 h. After cooling to 0°C,
a saturated aqueous ammonium chloride (150 mL) was added to the solution to give NPMoV which was purified by the
recrystallization from water, and dried in vacuo with heating at about 90°C. The preparation of [Pd(OAc)2–NPMoV/C] was
as follows: Pd(OAc)2 (333 mg) was dissolved in excess acetone and then activated carbon (3 g) was added. After stirring
overnight at room temperature, [Pd(OAc)2/C] was obtained in quantitative yield. To a suspended water of the [Pd(OAc)2/C]
(3.33 g) was added NPMoV (588 mg), and vigorously stirred for 3 h at room temperature. [Pd(OAc)2–NPMoV/C] was filtered
off, washed with water, and dried in vacuo with heating at about 90°C to give [Pd(OAc)2–NPMoV/C] in almost quantitative
yield.
7. (a) Yokota, T.; Fujibayashi, S.; Nishiyama, Y.; Sakaguchi, S.; Ishii, Y. J. Mol. Catal. A: Chem. 1996, 114, 113–122. (b)
Yokota, T.; Sakurai, Y.; Sakaguchi, S.; Ishii, Y. Tetrahedron Lett. 1997, 38, 3923–3926. (c) Sakurai, Y.; Sakaguchi, S.; Ishii,
Y. Tetrahedron Lett. 1999, 40, 1701–1704.
8. (a) Kolb, M.; Bratz, E.; Dialer, K. J. Mol. Catal. 1977, 2, 399–408. (b) Horowitz, H. H. J. Appl. Electrochem. 1984, 14,
779–790. (c) Miller, D. G.; Wayner, D. D. M. J. Org. Chem. 1990, 55, 2924–2927.
9. (a) Fujibayashi, S.; Nakayama, K.; Hamamoto, M.; Sakaguchi, S.; Nishiyama, Y.; Ishii, Y. J. Mol. Catal. A: Chem. 1996,
114, 105–117.