A Heterogeneous Tungsten Catalyst for Epoxidation of Terpenes and Tungsten-Catalyzed Synthesis of Acid-Sensitive Terpene Epoxides

Full text of DOI:10.1021/jo990790z

J . Org. Chem. 1999, 64, 7267-7270
7267
be much facilitated if a heterogeneous catalyst were
available that could handle even bulky substrates. How-
ever, known solid oxidation catalysts such as the molec-
ular sieve Ti Silicalite-1 (TS-1) not only increase the
acidity of aqueous H2O2; their small pore diameter also
limits the access to the active sites for fairly large
substrates.11 In the reactions of Table 1, a heterogeneous
catalyst is used that was obtained by exchange of a
commercial, macroreticular Amberlite IRA-900 with the
A Heter ogen eou s Tu n gsten Ca ta lyst for
Ep oxid a tion of Ter p en es a n d
Tu n gsten -Ca ta lyzed Syn th esis of
Acid -Sen sitive Ter p en e Ep oxid es
A´ıda L. Villa de P., Bert F. Sels, Dirk E. De Vos, and
Pierre A. J acobs*
Center for Surface Chemistry and Catalysis, Katholieke
Universiteit Leuven, Kardinaal Mercierlaan 92,
B-3001 Heverlee, Belgium
Venturello anion {PO4[WO(O2)2]4}3- 5c
In the catalyst
.
-
Received May 13, 1999
preparation, the resin was first converted into its NO3
form, as co-exchanged Cl- appeared to decrease the
selectivity of the epoxidation. Next, a solution of pre-
formed PW4O24[(C4H9)4N]3 was shaken with the Amber-
lite, and H2O2 was added during this exchange to keep
the peroxo W complexes intact.7 The solid (PW-Amb)
was thoroughly washed to remove nonexchanged peroxo
PW quaternary ammonium compounds. As 40% or less
of the anion exchange capacity (4.2 mequiv g-1) is
occupied by the PW-anions, the heterogeneity of the
catalyst is guaranteed, particularly in organic solvents.
In the reactions of Table 1, typically 7-10 g of the
desired product is obtained per gram of PW-Amb
catalyst, or 80 mol of product per mole of exchanged
PW4O243-. Note that TS-1 produces at most 4 g of epoxide
per gram of catalyst with 1-hexene or 1-octene as a
substrate before it is largely deactivated; the activity of
larger pore Ti molecular sieves such as Ti-MCM-41 is
even lower.11 This high productivity of PW-Amb is
coupled to a selectivity for epoxides that exceeds 90% for
limonene (2), for unsaturated C10 alcohols or their esters
(3-5, 7-9), and for 3-carene (12) (entries 1-5, 7, 9, 11,
and 12). Acetonitrile is a suitable solvent, but acetone
may be used as well. In methanol yields are much lower.
At longer reaction times and with more peroxide, diep-
oxides are easily formed, e.g., from 7 and 8 (entries 8 and
10).
The water-soluble substrate crotyl alcohol (13) is
converted with excellent selectivity to its epoxide, even
if all reagents are present in a single liquid phase (Table
1, entry 14). This is unusual for PW epoxidations, in
which partition of the epoxide product to an apolar
organic layer is generally desired to prevent hydrolysis
in the acid aqueous layer.5,6,9 Hence, while most two-
phase W oxidations have been performed with olefins
containing six or more carbon atoms, the single liquid-
phase oxidation with PW-Amb is clearly not subjected
to this limitation.
In tr od u ction
Terpenes are cheap and often chiral precursors to
fragrances, flavors, drugs, and agrochemicals.1 Oxyfunc-
tionalization of terpenes frequently starts with a selective
epoxidation.2 Although catalytic epoxidation is nowadays
dominant for many commodities and fine chemicals, the
synthesis of the major terpene epoxide, R-pinene oxide,
still employs the stoichiometric peracid route.3,4 In de-
signing a catalytic alternative, H2O2 is the preferred
reagent, but the choice of a (metal) catalyst is less
evident, particularly if a convenient catalyst separation
and product workup are desired or if one aims at the
formation of acid-labile epoxides. Most of the reported
tungsten catalysis is homogeneous and liquid biphasic,
with a quaternary ammonium compound enhancing
phase transfer of the peroxo W compound from the
aqueous to the organic layer.5-10
We here report a heterogeneous, reusable W catalyst
for the selective epoxidation of a series of terpene olefins.
An essential step in the preparation of this solid catalyst
is the ion exchange of a preformed peroxo PW-anion onto
a resin in the presence of H2O2. Moreover, by careful
choice of reaction conditions, phosphorus, and quaternary
ammonium additives, we have designed a homogeneous
W-based catalytic procedure for the production of labile
epoxides. This is particularly interesting, as W-catalyzed
epoxidation of R-pinene was till now an unresolved
challenge.
Resu lts a n d Discu ssion
A Heter ogen eou s P h osp h otu n gsta te Ca ta lyst for
Ter p en e Ep oxid a tion . Epoxidations with H2O2 would
* Tel: 32 16 321610. Fax: 32 16 321998. E-mail: pierre.jacobs.@
agr.kleuven.ac.be.
(1) Bauer, K.; Garbe, D.; Surburg, H. Common Fragrance and Flavor
Materials; Wiley-VCH: New York, 1997.
(2) Fehr, C. Angew. Chem., Int. Ed. Engl. 1998, 37, 2407.
(3) Sheldon, R. A.; Kochi, J . K. Metal-Catalyzed Oxidations of
Organic Compounds; Academic Press: New York, 1981.
(4) Ullmann’s Encyclopedia of Industrial Chemistry, 6th Ed., Elec-
tronic Release; Wiley-VCH: New York, 1998.
(5) (a) Venturello, C.; Alneri, E.; Ricci, M. J . Org. Chem. 1983, 48,
3831. (b) Venturello, C.; D′Aloisio, R. J . Org. Chem. 1988, 53, 1553.
(c) Venturello, C.; D′Aloisio, R.; Bart, J . C. J .; Ricci, M. J . Mol. Catal.
1985, 32, 107.
(6) (a) Ishii, Y.; Yamawaki, K.; Ura, T.; Yamada, H.; Yoshida, Y.;
Ogawa, M. J . Org. Chem. 1988, 53, 3587. (b) Sakaguchi, S.; Nishiyama,
Y.; Ishii, Y. J . Org. Chem. 1996, 61, 5307.
(7) Duncan, D. C.; Chambers, R. C.; Hecht, E.; Hill, C. L. J . Am.
Chem. Soc. 1995, 117, 681.
(8) Bo¨sing, M.; No¨h, A.; Loose, I.; Krebs, B. J . Am. Chem. Soc. 1998,
120, 7252.
(9) (a) Sato, K.; Aoki, M.; Ogawa, M.; Hashimoto, T.; Panyella, D.;
Noyori, R. Bull. Chem. Soc. J pn. 1997, 70, 905. (b) Sato, K.; Aoki, M.;
Hashimoto, T.; Noyori, R. J . Org. Chem. 1996, 61, 8310.
(10) Prandi, J .; Kagan, H. B.; Mimoun, H. Tetrahedron Lett. 1986,
27, 2617.
Conversion of unsaturated esters such as 7 and 8
proceeds optimally at 311 K, while subambient temper-
ature is most suitable for the corresponding alcohols. In
geraniol (3) and nerol (4), oxidation of the alcohol function
represents about 5% of the products (Table 1, entries 3
and 4). Even with a secondary enol such as 2-cyclohexen-
1-ol (6), the epoxidation still dominates over ketonization,
with a 71% epoxide selectivity (Table 1, entry 6). This is
noteworthy, as tungstate catalysts or phosphotungstate
associations have been documented to effect ketonization
of particularly secondary alcohols with H2O2, for instance,
(11) (a) Clerici, M. G.; Ingallina, P. J . Catal. 1993, 140, 71. (b) Blasco,
T.; Corma, A.; Navarro, M. T.; Pe´rez Pariente, J . J . Catal. 1995, 156,
65.
10.1021/jo990790z CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/31/1999

7268 J . Org. Chem., Vol. 64, No. 19, 1999
Notes
Ta ble 1. Ep oxid a tion of Mon oter p en es a n d Cr otyl Alcoh ol w ith H2O2 a n d th e Heter ogen eou s P W-Am ber lite Ca ta lysta
olefin
epoxide
entry
substrate
limonene (2)
T, °C (t, h)
conversion (%)
selectivity (%)
product distribution (%)
1
2c
3
4
5
38 (24)
38 (24)
0 (24)
0 (24)
38 (40)
0 (40)
38 (40)
38 (72)
38 (24)
38 (72)
38 (24)
38 (24)
38 (24)
38 (24)
84
82
74
71
100
48
94
99
90
99
90
55
56
82
93
92
94
95
1
76
92
84
92
76
96
97
97
99
monoepoxide (85),b diepoxide (8)
2
geraniol (3)
nerol (4)
linalool (5)
2-cyclohexen-1-ol (6)
geranyl acetate (7)
7
neryl acetate (8)
8
linalyl acetate (9)
3-carene (12)
12
monoepoxide (84),d diepoxide (10), geranial (6)
monoepoxide (81),e diepoxide (14), neral (4)
monoepoxide (1), 10 + 11 (96)f
epoxy-ol (71),g enone (12), epoxy-one (5)
monoepoxide (70),h diepoxide (22)
monoepoxide (25), diepoxide (59)
monoepoxide (68),j diepoxide (24)
monoepoxide (15), diepoxide (61)
6,7-monoepoxide (94)k
6
7
8i
9
10i
11
12
13c
14
trans epoxide (97)
l
crotyl alcohol (13)
trans:cis epoxide ) 16
a
b
Procedure: 1 mmol of olefin, 2 mmol of H2O2, 20 mg of catalyst, 1.5-4 mL CH3CN. 1,2:8,9 epoxide ) 30, cis(1,2):trans(1,2) epoxide
) 1.15. c Run with a reused catalyst. 2,3:6,7 epoxide ) 9.4. e 2,3:6,7 epoxide ) 6.6. f Five rings:six rings ) 2.3. syn:anti ) 1.8. 6,7:2,3
epoxide ) 31. 4 mmol of H2O2. 6,7:2,3 epoxide ) 22. 6,7:1,2 epoxide ) 49. Commercial crotyl alcohol contains 95% trans isomer.
d
g
h
i
j
k
l
Ch a r t 1
polymeric host not only provides heterogenization but
also induces subtle changes in regio- and stereoselectiv-
ity.
After simple filtration of the macroreticular catalyst
beads, the filtrate contains, apart from the solvent, the
reaction product as sole organic component. While in
typical homogeneous reactions the product must be
distilled to separate it from quaternary N phase transfer
catalysts or from byproducts of the peracid, this step can
be avoided with the heterogeneous catalyst. Catalyst
reusability was tested for several substrates and proved
satisfactory with respect to conversion and selectivity in
all cases. Data for a second run with 2 or 12 and a
recuperated PW-Amb catalyst are included in Table 1
(entries 2 and 13). The advantages of the heterogeneous
reaction are particularly well illustrated in the oxidation
of linalool (5). In this reaction, the 6,7-epoxide directly
rearranges to a mixture of the diastereomeric five- and
six-ring tetrahydrofurans and pyrans (10, 11), with an
overall yield of 96% (Table 1, entry 5). Exactly the same
product composition, termed linalool oxide, is obtained
with a stoichiometric peracid.1
P r ep a r a tion of Acid -Sen sitive Ter p en e Ep oxid es
w ith Tu n gsten Ca ta lysts. As activation of aqueous
H2O2 is often based on the Lewis acidity of the catalysts,
there are only a few catalysts that operate in inherently
neutral conditions.3 Manganese catalysts do not cause
epoxide solvolysis but face other drawbacks, e.g., pro-
nounced steric hindrance at the active site, which makes
them less suitable for reactions with trisubstituted olefins
such as R-pinene (15).13 With a catalytic amount of CH3-
ReO3 and H2O2, 15 is epoxidized selectively, but buffering
of the Lewis acidity requires up to equimolar amounts
of pyridine or bipyridine, which are largely consumed
with formation of the corresponding N-oxides.14 Typical
W procedures from literature do not allow prevention of
hydrolysis or rearrangement of the epoxides. For in-
in the reaction of carveol.12 In our hands, the recent
W-based epoxidation protocol of Sato et al.9a leads from
6 to 2-cyclohexen-1-one as the major product (68% enone
selectivity; Table 2, entry 2).
The typical properties of W catalysis, such as ste-
reospecificity, are well preserved in the heterogeneous
catalyst. Thus, 4 gives the cis-2,3-epoxy-ol but not the
trans product (2,3-epoxygeraniol). There are indications
that in the oxidation of enols over PW-Amb, the direct-
ing effect of the hydroxyl group on the epoxidation is less
decisive than for other W-catalyzed reactions. Thus, from
6, the syn and anti epoxides are obtained in a 1.8 to 1
ratio (Table 1, entry 6), while this ratio is generally
higher for homogeneous W catalysts (6 to 1; Table 2,
entry 2). Analogous effects can be observed in the
regioselectivity of the epoxidation of 3. While alcohol
coordination on W usually directs the epoxidation largely
to the 2,3-bond, the 6,7-bond is now less disfavored for
epoxidation, and this leads to doubly epoxidized products.
Summarizing, the embedding of the PW-anion in the
(13) (a) Battioni, P.; Renaud, J . P.; Bartoli, J . F.; Reina-Artiles, M.;
Fort, M.; Mansuy, D. J . Am. Chem. Soc. 1988, 110, 8462. (b) De Vos,
D. E.; Sels, B.; Reynaers, M.; Subba Rao, Y. V.; J acobs, P. A.
Tetrahedron Lett. 1998, 39, 3221.
(14) (a) Villa, A. L.; De Vos, D. E.; Montes, C.; J acobs, P. A.
Tetrahedron Lett. 1998. (b) Herrmann, W. A.; Fischer, R. W.; Marz,
D. W. Angew. Chem., Int. Ed. Engl. 1991, 30, 1638. (c) Rudolph, J .;
Reddy, K. L.; Chiang, J . P.; Sharpless, K. B. J . Am. Chem. Soc. 1997,
119, 6189. (d) Yudin, A. K.; Sharpless, K. B. J . Am. Chem. Soc. 1997,
119, 11536. (e) Cope´ret, C.; Adolffson, H.; Sharpless, K. B. Chem.
Commun. 1997, 1565. (f) Rudler, H.; Gregorio, J . R.; Denise, B.;
Bre´geault, J . M.; Deloffre, A. J . Mol. Catal. 1998, 133, 255.
(12) (a) Prat, D.; Delpech, B.; Lett, R. Tetrahedron Lett. 1986, 27,
711. (b) Sato, K.; Aoki, M.; Takagi, J .; Noyori, R. J . Am. Chem. Soc.
1997, 119, 12386. (c) Neumann, R.; Khenkin, A.; J uwiler, D.; Miller,
H.; Gara, M. J . Mol. Catal. 1997, 117, 159. (d) Venturello, C.; Gambaro,
M. J . Org. Chem. 1991, 56, 5924.

Notes
entry
J . Org. Chem., Vol. 64, No. 19, 1999 7269
Ta ble 2. Hom ogen eou s Ca ta lytic Syn th esis of (Acid -Aen sitive) Ep oxid es w ith th e Ven tu r ello Com p lex 1 a n d
(Am in om eth yl)p h osp h on ic Acid a s th e Co-ca ta lysta
mole % vs olefin
T, °C
olefin
epoxide
substrate
1-decene (14)
NH2CH2PO3H2
1
Na2WO4 (t, h) conversion (%) selectivity (%)
comments
1
2
3
1
1
1
0
0
0
2.5
2.5
2.5
90 (4)
60 (4)
90 (4)
99
57
29
90
24
0
2-cyclohexen-1-ol (6)
R-pinene (15)
epoxy-ol (24%),b enone (68%)
diol (43%), campholenic aldehyde (10%),
other rearrangement products
4
5
6
7
8
9
R-pinene (15)
2
2
2
0
2
2
2
0.6
2
2
1
1.7
1
1
1.6
0
0.3
1
0
3
0
3
2.6
0
7
0.8
2.7
60 (2)
60 (1)
60 (1)
60 (1)
60 (1)
60 (2.5)
60 (2)
60 (1)
60 (2)
83
83
100
43
42
95
17
40
92
92c
91
53
93
88
72
90
87
85
15
15
15
15
15
no pH control (pH ) 2.1)
no extra P source
P-source ) H3PO4
P-source ) ethanolamine phosphate
no preformed catalyst
0.6 equiv H2O2
10 15
11 15
12 15
solvent: toluene
13 3-carene (12)
14 linalool (5)
15 1-phenyl-1-cyclohexene (16)
16 indene (17)
1
9
6
7
1
2
11
7
7
60 (4)
60 (4)
60 (4)
60 (4)
97
85
97
96
97
68
83
68
trans epoxide
6,7-monoepoxide
pHaq ) 5
3.7
2.6
2.5
pHaq ) 5
a
Procedures: Entries 1-3: according to ref 9a: 1 equiv olefin, 1.5 equiv aqueous 35% H2O2, 0.01 equiv [(C8H17)3NCH3]HSO4;
NH2CH2PO3H2, and Na2WO4‚2H2O as indicated (mol % of olefin); 0.6 mL toluene per mmole substrate. No pH control. (entries 4-16):
1 equiv olefin, 2 equiv aqueous 35% H2O2; P compound (NH2CH2PO3H2, except for entries 7-9), 1 ) PW4O24[(C8H17)3NCH3]3 and
Na2WO4‚2H2O as indicated (mol %); 1 mL benzene per mmole substrate. pH was brought to 4.2 ( 0.2 with aqueous NaOH (except in
b
entries 6, 15, 16). In entry 10, 3 mole % [(C8H17)3NCH3]Cl was added as a phase transfer catalyst. syn:anti ) 6. c 99% of the R-pinene
oxide is trans.
stance, while in the 1-decene (14) epoxidation the yield
reported by Sato et al.9 is satisfactorily reproduced (90%;
Table 2, entry 1), the same procedure leads to essentially
zero epoxide yield with 15 (entry 3). Characteristically,
in previous reports on W- or PW-catalyzed synthesis of
labile or terpene-derived epoxides, the reaction of R-pinene
is not addressed.5b,6b,10
However, our data show that in appropriate conditions
15 can be epoxidized with W, with 92% selectivity at over
80% olefin conversion (eq 1). Table 2 contains some of
are mixed in situ, activities are much lower (entry 10).
The optimized reaction can be conducted with excess
H2O2, leading to almost complete conversion, or with an
understoichiometric amount of peroxide, with recovery
of the remaining 15 (entries 4 and 11). In both cases, the
epoxide selectivity is around 85-90%. This is remarkable,
as in Venturello’s original procedure excess olefin is
necessary to preserve high epoxide selectivity.5b In our
experience, 1 mL of solvent is required per mmole of
substrate to favor partition of the epoxide to the organic
phase; instead of halocarbon solvents, benzene and even
toluene give excellent results (entry 12).
Our method was successfully expanded to other ter-
pene substrates such as 12 (94% yield on olefin charged)
(entry 13). For 5, the intramolecular cyclization can
largely be prevented, and the 6,7-epoxide is the major
product (68% yield on olefin reacted) (entry 14). Nonter-
pene substrates with sensitive epoxides are also suitable
starting products; for instance, in reactions with an
aqueous layer at pH 5, 1-phenyl-1-cyclohexene (16) and
indene (17) were converted into the epoxide products as
evidenced by NMR (entries 15 and 16).
the essential steps in the optimization of the reaction.
The best results are obtained when P and W are preas-
sociated in a Venturello complex (PW4O24[(C8H17)3-
NCH3]3), which also contains the quaternary ammonium
phase transfer agent (entry 4). Part of the W may be
introduced as the disodium salt into the aqueous phase
without major effects on the reaction (entry 5). Adjusting
the pH of the aqueous phase to 4.2 with aqueous NaOH
somewhat lowers the reaction rate but has a large
positive impact on the selectivity (entry 6). The addition
of the extra P source (aminomethyl)phosphonic acid
induces a clear rate acceleration, combined with an
excellent epoxide selectivity (compare entries 5 and 7).
This effect is not observed when phosphoric acid is used
as the P source, even if in both cases the pH is adjusted
to 4.2 (entry 8). Better results are obtained with other
organic P compounds, such as ethanolamine phosphate
(entry 9).
Con clu sion
We have explored and widened the scope of tungsten
catalysis for epoxidation of terpenoid and related olefins.
A heterogeneous catalyst is now available for most
substrates with reasonably stable epoxides. The catalyst
can be used in small concentrations and facilitates
product workup. Moreover, we report the first W-cata-
lyzed epoxidation of R-pinene, in a biphasic reaction with
a buffered aqueous layer. The use of (aminomethyl)-
phosphonic acid as a cocatalyst is beneficial for the
reaction rate while keeping the epoxide selectivity high.
For heterogeneous and for homogeneous catalysis, it is
advantageous to employ preformed peroxo PW-anions.
Exp er im en ta l Section
Ma ter ia ls. All commercial products were of the highest grade
available and were used as such. Hydrogen peroxide was a 35%
aqueous solution (Akros) or a 50% solution (Rectapur). The
When tungstate, the salt of the quaternary ammonium
component (Aliquat 336) and the phosphorus compound

7270 J . Org. Chem., Vol. 64, No. 19, 1999
Notes
Venturello complexes PW4O24[(C4H9)4N]3 and PW4O24[(C8H17)3-
Product analysis was done with a GLC (50 m Chrompack CP-
Sil 5 column). In GLC calculations, all peaks amounting to at
least 0.3% of the total products were taken into account, making
the analysis much more precise than even a routine NMR
determination. Identity of epoxide products was confirmed by
300 MHz 1H and 13C NMR. Spectra were compared with those
of authentic compounds for linalool oxide, cis- and trans-1,2-
limonene oxide, and R-pinene oxide. Listed data (1H and/or 13C)
are available for R-pinene oxide,15 1,2-limonene oxide,15,16 3-care-
ne oxide,16 1,2-epoxyindane,17 6,7-epoxylinalyl acetate,18 6,7-
epoxygeranyl acetate,18 6,7-epoxyneryl acetate,18 2,3-epoxyge-
raniol,19 and 2,3-epoxynerol.20,21
NCH3]3 were prepared as described in the literature.5b,c
A
reported procedure was also followed for preparation of the phase
transfer agent [(C8H17)3NCH3]HSO4.9b
P r ep a r a tion of th e Heter ogen eou s Ca ta lyst P W-Am b.
Amberlite IRA 900 (anion exchange capacity, 4.2 mequiv per g
dry weight) was converted into its NO3- form in a 0.2 M NaNO3
solution and dried. One gram of PW4O24[(C4H9)4N]3 was dis-
solved in 6 mL of acetone and 2 mL of 35% H2O2, and 0.8 g of
the Amberlite was added to this solution. Ion exchange was
performed by shaking at room temperature. After 16 h, the solid
was filtered; washed with water, water-acetone (50-50), and
acetone; and eventually air-dried.
Ep oxid a tion P r oced u r es. (1) With th e Heter ogen eou s
P W-Am b Ca ta lyst (Table 1). A 20 mg portion of catalyst is
suspended in a solution of 1 mmol of olefin in 1.5-4 mL of CH3-
CN, and 50% H2O2 (2 mmol) is added. The mixture is stirred at
0 or 38 °C. After reaction, the catalyst beads are filtered, CH3-
CN is evaporated, and EtOEt is added. Evaporation of the
organic layer leads to the isolated product.
Ack n ow led gm en t. We are grateful to Colciencias
(A.L.V.), IWT (B.F.S.), and FWO (D.E.D.V.) for fellow-
ships. This work is sponsored by the Belgian Federal
Government in a IUAP program Supramolecular Ca-
talysis.
(2) Liqu id Bip h a sic Ep oxid a tion (Table 2, entries 1-3),
e.g., of 14. Na2WO4‚2H2O, NH2CH2PO3H2, aqueous 35% H2O2,
and [(C8H17)3NCH3]HSO4 are mixed in a 0.025:0.01:1.50:0.01
ratio. After vigorous stirring for 15 min at room temperature,
the olefin (1 equiv) diluted in toluene (0.6 mL per mmole of
substrate) is added. Reaction is conducted for 4 h at 60-90 °C
(750 rpm).
Su p p or tin g In for m a tion Ava ila ble: Physical data of the
products. This material is available free of charge via the
Internet at http://pubs.acs.org. This material is contained in
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, and can be ordered from the
ACS; see any current masthead page for ordering information.
(3) Syn th esis of Acid -Sen sitive Ter p en e Ep oxid es (e.g.,
R-pinene epoxide; Table 2, entry 5). An aqueous mixture of 35%
H2O2, NH2CH2PO3H2, PW4O24[(C8H17)3NCH3]3, and Na2WO4‚
2H2O (molar ratio 2:0.02:0.01:0.03) is brought to pH 4.2 with
0.5 N NaOH. This mixture is then added to the olefin (1 equiv)
dissolved in the solvent (1 mL of benzene per mmole of olefin).
The reaction mixture is stirred at 500 rpm and 60 °C. After
reaction, the organic layer is washed with a phosphate buffer
and with 10% aqueous Na2SO3 to decompose unreacted H2O2.
Cooling in a freezer (e.g., for 3 h at -20 °C) causes precipitation
of most of the quaternary ammonium compound, and after
solvent evaporation the product is ready for NMR analysis. For
other entries in Table 2 (e.g., 13-16), the procedure was modified
as indicated in Table 2.
J O990790Z
(15) Pouchert, C.; Behnke, J . The Aldrich Library of 13C and 1H FT
NMR spectra; Aldrich Chemical Co.: Milwaukee, 1993.
(16) Fdil, N.; Romane, A.; Allaoud, S.; Karim, A.; Castanet, Y.;
Mortreux, A. J . Mol. Catal. 1996, 108, 15.
(17) Boyd, D. R.; Sharma, N. D.; Smith, A. E. J . Chem. Soc., Perkin
Trans. 1 1982, 2767.
(18) Takai, T.; Hata, E.; Yamada, T.; Mukaiyama, T. Bull. Chem.
Soc. J pn. 1991, 64, 2513.
(19) Li, W.; Li, Y.; Li, Y. J . Chin. Chem. Soc. 1995, 42, 701.
(20) Ray, N. C.; Raveendranath, P. C.; Spencer, T. A. Tetrahedron
1992, 48, 9427.
(21) Van Hijfte, L.; Kolb, M. Tetrahedron 1992, 48, 6393.