Oxidation of allylic alcohols, amines, and sulfides mediated by assembled triphase catalyst of phosphotungstate and non-cross-linked amphiphilic copolymer

Article abstract of DOI:10.1016/j.tet.2004.02.072

A novel catalyst PWAA, an assembled complex of phosphotungstic acid (H ₃PW₁₂O₄₀) and a non-cross-linked copolymer of N-isopropylacrylamide with an ammonium, was developed. It is an amphiphilic, cross-linked, and supramolecular insoluble complex and showed catalytic activity on oxidation with aqueous hydrogen peroxide. PWAA, used in 2.7×10 ^-5-2.0×10^-3molequiv., catalyzed oxidation of allylic alcohols, amines, and sulfides efficiently. The turnover number (TON) of PWAA reached up to 35,000. PWAA showed a good stability in organic/aqueous media and was reused three to five times.

Full text of DOI:10.1016/j.tet.2004.02.072

Tetrahedron 60 (2004) 4087–4096
Oxidation of allylic alcohols, amines, and sulfides mediated by
assembled triphase catalyst of phosphotungstate and
non-cross-linked amphiphilic copolymer
Yoichi M. A. Yamada, Hidetsugu Tabata, Masato Ichinohe, Hideyo Takahashi
*
and Shiro Ikegami
Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Kanagawa 199-0195, Japan
Received 26 January 2004; accepted 19 February 2004
Abstract—A novel catalyst PWAA, an assembled complex of phosphotungstic acid (H PW O ) and a non-cross-linked copolymer of
3
12 40
N-isopropylacrylamide with an ammonium, was developed. It is an amphiphilic, cross-linked, and supramolecular insoluble complex and
2
5
23
showed catalytic activity on oxidation with aqueous hydrogen peroxide. PWAA, used in 2.7£10 –2.0£10 mol equiv., catalyzed
oxidation of allylic alcohols, amines, and sulfides efficiently. The turnover number (TON) of PWAA reached up to 35,000. PWAA showed a
good stability in organic/aqueous media and was reused three to five times.
q 2004 Elsevier Ltd. All rights reserved.
1
. Introduction
Over the past few decades, a considerable number of studies
have been made on triphase catalysts which were
immobilized with cross-linked polystyrene resins, silica
gels or metals. These catalytic systems, however, generally
resulted in lower catalytic activity compared with their
soluble counterparts, and were often obliged to use
A development of phase-transfer solid-phase catalyst that
mediates aqueous–organic biphase reactions is one of the
most important issues for recent synthetic organic chemistry
and industrial engineering. Using such triphase catalysts
enables effective reactions between organic substrates and
1
,2
3
hazardous chlorohydrocarbon solvents. Besides, reuse of
2
water-soluble reagents. In addition to this, these solid-
these catalysts was often difficult owing to the gradual
decline of the catalytic activity. These problems made them
less practical. Therefore, we decided to concentrate on
developing triphase catalysts that were highly active and
reusable.
phase catalysts are easily separated by filtration or
decantation from the system and are reused without any
treatments. Hence, this catalytic system can enhance
economy of the reaction and decrease environmental
pollution under ideal conditions.
In traditional triphase catalysts, as we have mentioned
before, a catalytic species was anchored to a linker that was
immobilized to a polymer resin or silica gel (Scheme 1,
above). In our approach, however, the insoluble catalysts
were constructed from self-assembly process of non-cross-
linked amphiphilic copolymer ligands and inorganic
In order to realize this triphase catalytic oxidation system,
one may say that using water-soluble oxidants such as
hydrogen peroxide is suitable. Although many toxic
1
reagents such as Cr(VI), Mn(VII), Os(VIII) and Pb(IV)
have been utilized for oxidation, such heavy metal species
are stoichiometric or substoichimetric oxidants, and thus
many toxic wastes must be disposed. On the contrary,
hydrogen peroxide is sustainable and economical; it is a
4
species. This process would promote the cross-linking of
the copolymer by the inorganic species to provide
networked, supramolecular, and insoluble complexes
(Scheme 1, below). They might possess many mesopores
where the inorganic species would be tightly supported by
many ligands not to be dissociated. We expected such
complexes should act as highly active catalysts based on the
following points: (1) the complexes have a characteristic
high-to-volume ratio to react with a substrate and a reagent,
1
c
cheap and clean oxidant transformed into harmless water.
Thus, the oxidation system promoted by triphase catalysts
with hydrogen peroxide can fulfill all the requirements of
economy, efficiency, and safety.
Keywords: Catalysis; Oxidation; Polymer support; Self-assembly;
Tungsten and compounds.
(2) they can capture these reagents effectively by their
mesopores, and (3) the amphiphilic copolymers and the
inorganic species might construct effective catalytic sites
*
Corresponding author. Tel.: þ81-426-85-3728; fax: þ81-426-85-1870;
e-mail address: shi-ike@pharm.teikyo-u.ac.jp
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.02.072

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Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
Scheme 1. Hypothesis of formation of a self-assembled complex for an insoluble oxidation catalyst.
with high affinity to both hydrophobic and hydrophilic
reagents.
2. Preparation of a triphase catalyst PWAA
PWAA was prepared as shown in Scheme 2. Ammonium
salt 4 was synthesized from commercially available N-[3-
(dimethylamino)propyl]acrylamide with 1-bromododecane
in 92% yield. Random copolymerizations of 4 with
12 mol equiv. of 5 were performed in the presence of
0.04 mol equiv. of AIBN in t-BuOH at 75 8C for 48 h,
resulting in that non-cross-linked polymer 6 was formed. It
was an amphiphilic polymer that was soluble in water,
t-BuOH, and CH Cl . The ratio of the N-isopropylacryl
We herein report the full detail of our approach: a
development of a highly active triphase catalyst PWAA
(
3), formed from phosphotungstic acid (H PW O ) (1)
3 12 40
and poly{[3-(acryloylamino)propyl]dodecyldimethyl-
ammonium nitrate}-co-(N-isopropylacrylamide) } (2) and
its application to oxidation of allylic alcohols, amines and
1
2
5
sulfides. It was found that PWAA has a good catalytic
activity on oxidation in both aqueous and organic solvent. It
should be noted that the turnover number (TON¼mol of a
product/mol of a catalyst) of PWAA reached up to 35,000.
2
2
amide unit to the ammonium unit to be 12/1 was determined
1
by H NMR. The bromide 6 was ion-exchanged to the
Scheme 2. Preparation of a novel triphase catalyst PWAA with the structure 3.

Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
4089
6
nitrate 2. The molecular weight of 2 was wide-ranging
thousands to tens of thousands) as a result of gel-
possessed many pores, whose diameter was about 1–10 mm
(left) and hundreds nanometer or less (center). Further
magnification (£50,000) showed many projections those
lengths were less than 100 nm (right); all these things make
it clear that PWAA has a high surface-to-volume ratio and
many reactive sites. The further structural investigation of
the catalyst is now under the way.
(
permeation chromatography relative to polystyrene
standards. Thus, complexation to form PWAA was carried
out according to the procedure for the preparation of
7
[
p-C H N(CH ) CH ] PW O .
5
A
self-assembly
5
2 15
3 3
12 40
process of 1 with 2 (3 mol equiv. as an ammonium unit)
in water at room temperature resulted in the formation of
white insoluble precipitates simultaneously. After stirring
for 7 days at the same temperature, the resulted precipitate
was washed and dried to give PWAA as white lumps.
PWAA were insoluble in H O and organic solvents such as
8
3. Epoxidation of allylic alcohols catalyzed by PWAA
2
MeOH, EtOH, i-PrOH, AcOEt, Me CO, CH Cl , toluene,
2
Et O and hexane.
2
With the insoluble complex PWAA in hand, the epoxidation
of allylic alcohols with aqueous H O under the organic
2
2
2
2
2,13
1
solvent-free conditions was examined.
We were pleased
to find that PWAA showed a very high catalytic activity on
To elucidate the structure of PWAA, several spectroscopic
measurements were examined. The elementary analysis
showed that one complex unit of 3·22H O. The infrared
2
5
epoxidation. In the presence of 2.7£10 mol equiv. of
PWAA, the reaction of phytol (7a) with 2 mol equiv. of
30% aqueous H O resulted in the corresponding epoxy
2
spectrum of PWAA exhibited strong vibrations at 1080
1
2
2
2
(
PvO), 978 (WvO), 897 and 818 cm , while that of 1
alcohol 8a in 94% yield (Scheme 3). TON of PWAA was
approximately 35,000. This result showed that PWAA has a
excellent catalytic activity among the precedent.
2
1
exhibited them at 1080, 982, 893 and 808 cm . Viewed in
this light, the structure of the phosphotungstic acid unit of
PWAA can be regarded as that of 1.
3
1
Furthermore, we analyzed PWAA by gel-phase P NMR; a
broad singlet peak was detected at 213 ppm (Fig. 1). Since
it was reported that the signals of H PW O and
3
12 40
[
similar frequency (214.7 ppm and 214.5 ppm,
p-C H N(CH ) CH ] PW O were observed at the
5 5 2 15 3 3 12 40
9
10
respectively), it would be supported that phosphotungstate
in PWAA maintained the heteropolyacidic structure such as
3
2 40
2 11
the Keggin type (PW O ).
1
Scheme 3. Epoxidation of phytol (7a) promoted by PWAA.
Since the catalytic activity of PWAA was evaluated, a series
of epoxidation of several allylic alcohols was performed in
2
4
the presence of 5.0£10 mol equiv. of PWAA (Table 1).
Hydrophobic substrates of 7a and farnesol (7b) were
converted to the corresponding epoxides in high yields.
Epoxidation of 7a proceeded in 7 h at room temperature to
give 8a in 96% yield with TON reaching approximately
2000 (entry 1). In the reaction of 7b, 2,3-epoxy alcohol 8b
was obtained in 84% yield (entry 2). In this case, other
trialkylsubstituted alkene moieties were intact. The epoxi-
dation of less hydrophobic geraniol (7c) was messy to afford
3
1
Figure 1. A gel-phase P NMR chart of PWAA.
8
(
c in 12% yield owing to acidic hydrolysis of the epoxide
entry 3). We found that the addition of a trace amount of
pyridine was effective to reduce an acidity in this
A scanning electron microscope (SEM) of PWAA was also
investigated (Fig. 2). PWAA was treated with gold vapor by
the sputter-coating method. It was observed that PWAA
1
4
system and thus to prevent the epoxide-opening reactions.
The reaction of 7c in the presence of PWAA and
2
3
6
.0£10 mol equiv. of pyridine for 15 h resulted in the
formation of 8c in 80% yield (entry 4), where the C(6)–(7)
double bond was not affected. Under identical conditions,
trisubstituted allylic alcohols such as an exocyclic allylic
alcohol 7d and a linear one 7e provided the corresponding
epoxides in high yields (entries 5 and 6). Although
disubstituted allylic alcohols were less reactive, they were
converted to the corresponding epoxides in quantitative
2
3
yields by using 2.0£10 mol equiv. of PWAA (entries 7
and 8). Besides, the diasteroselective epoxidation of
2-methyl-2-octen-4-ol (7h) furnished the threo-selective
Figure 2. Scanning electron micrographs (SEM) of PWAA; (left): scale
bar: 10 mm; (center): scale bar: 500 nm; (right): scale bar: 100 nm.

4090
Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
Table 1. Epoxidation of allylic alcohols promoted by PWAA
a
Entry
Substrate
3b (mol equiv.) Pyridine (mol equiv.) Time (h)
Yield (%)
2
2
4
4
1
2
7a 5.0£10
—
7
8a:96
7b 5.0£10
—
—
13
8b:84
2
2
4
4
3
4
7c 5.0£10
7c 5.0£10
37
15
8c:12
8c:80
23
6.0£10
6.0£10
2
4
4
23
23
5
6
7d 5.0£10
12
13
8d:83
8e:96
2
7e 5.0£10
6.0£10
2
2
3
3
22
22
7
8
7f 2.0£10
9.6£10
2.4£10
30
33
8f:quant
8g:quant
7g 2.0£10
2
3
3
22
22
9
7h 2.0£10
7i 2.0£10
7j 2.0£10
7k 2.0£10
7l 2.0£10
9.6£10
2.4£10
2.4£10
2.4£10
2.4£10
85
—
24
—
—
8h:73 (threo/erythro¼91:9)
2
b
1
1
1
1
0
1
2
3
2
2
2
3
3
3
22
22
22
c
b
b
a
b
c
Isolated yields.
The product was not isolated because the reaction was messy.
No reaction.
epoxy alcohol 8h in 73% yield (threo/erythro (91:9)) (entry
).
pivaloyl ester under identical conditions did not proceed at
all. Besides, the mixture of phytol (7a) and cyclohexene (7j)
resulted in the quantitative conversion of phytol and the no
reaction of cyclohexene under the identical conditions
9
We further investigated the oxidation of cyclic allylic
alcohol. In the case of 2-cyclohexen-1-ol (7i), decompo-
sition of the product was so fast that the reaction was messy.
This result might suggest that PWAA was not able to
activate a s-trans allylic alcohol efficiently. In respect of
chemoselectivity, cyclohexene (7j), an unmodified alkene,
was not converted to cyclohexene oxide at all. Moreover,
the epoxidation of homoallylic alcohols 7k and 7l was also
slow and did not provide the corresponding products. These
results indicated that hydroxyl group at allylic position was
essential to proceed the epoxidation efficiently.
For reasons mentioned above, we investigated the proximity
effect of allylic alcohol (Scheme 4). Epoxidation of a
phytol-methyl ether, a phytol-acetyl ester and a phytol-
Scheme 4. The epoxidation of phytol derivatives.

Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
4091
(
Scheme 5). Considered these results, epoxidation was
promoted by the interaction of hydroxyl group of allylic
alcohol with PWAA which is similar to early transition
1
5
metal catalyses.
Moreover, recycling of PWAA in case of 7a was examined
as shown in Scheme 6. It was found that PWAA was reused
three times; in the first to third cycle runs, the product 8a
was given in 96, 93, and 97% yields, respectively. The
activity of PWAA was unchanged under the oxidation
conditions through the consecutive runs, although PWAA
was pulverized through runs.
4. Oxidation of amines catalyzed by PWAA
Scheme 5. Epoxidation of the mixture of phytol and cyclohexene promoted
by PWAA.
Since PWAA efficiently promoted the epoxidation of allylic
alcohols, we applied this oxidation to heteroatoms:
1
6,17
secondary amines and sulfides.
Oxidation of secondary
amines is the most straightforward method and the direct
route to prepare nitrones, which are important substrates for
the synthesis of nitrogen-containing bioactive compounds.
It was beforehand confirmed that no oxidation of dibenzyl-
amine (9a) with hydrogen peroxide was observed at
room temperature. On the contrary, addition of 2£
2
3
1
0
mol equiv. of PWAA to this reaction system
proceeded oxidation to give the corresponding nitrone
1
8
(
10a) in 86% yield (Table 2, entry 1). Bis(p-substituted
benzyl)amines were also converted to the corresponding
oximes under similar conditions. The reaction of bis[(4-
trifluoromethyl)benzyl]amine (9b) proceeded smoothly to
afford 10b in 90% yield. TON of PWAA in this oxidation
reached 450. However, bis(4-chlorobenzyl)amine (9c) and
Scheme 6. Epoxidation of phytol (7a) catalyzed by recycled PWAA.
Table 2. Oxidation of secondary amines by PWAA
1
R
2
R
a
Entry
Amines
Temperature (8C)
Time (h)
Nitrone
Yield (%)
1
2
3
4
5
6
7
8
9
9a
9b
9c
9d
9e
9f
9g
9h
9i
Ph
p-CF
p-Cl–C
p-MeO–C
p-MeO–C
Ph
Ph
p-CF
p-Cl–C H
p-MeO–C
rt
rt
rt
rt
rt
rt
40
rt
24
24
24
48
24
24
24
24
12
10a
10b
10c
10d
89
90
56
62
3
–C
6
H
4
3
–C
6
H
4
6
H
4
6
6
6
4
6
H
H
4
4
H
4
0
0
p-CF
p-CF
3
–C
–C
6
H
H
4
4
10eþ10
94 (10eþ10e ¼1.7/1)
0
0
3
6
10fþ10f
80 (10fþ10f ¼1.3/1)
0
0
Ph
(CH
p-CN–C
Ph
6
H
4
10gþ10g
71 (10gþ10g ¼1.5/1)
3
)
3
10h
10i
34
70
rt
1
1
0
1
9j
rt
rt
12
12
10j
30
b
9k
—
a
Isolated yields.
The product was not isolated because the reaction was messy.
b

4092
Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
2
2
bis(4-methoxybenzyl)amine (9d) were converted to 10c and
0d in moderate yields. We further examined the regio-
12a–k in low to moderate yields rather than sulfones
13a–k. Meeting our expectations, PWAA efficiently
proceeded the oxidation of sulfides to give sulfones under
1
selective oxidations of bis(p-substituted benzyl)amines.
Although it seemed reasonable that the deprotonation took
place at more acidic benzylic position selectively, the
reactions gave nitrones in 71–94% yield albeit with low
2
3
similar conditions. In the presence of 2£10 mol equiv. of
PWAA, 11a was converted into 13a in 97% yield (entry 1).
TON of PWAA reached approximately 500. The substituted
aryl methyl sulfides were also converted to the correspond-
ing sulfones in high yields (84–90%) (entries 3, 5 and 7).
Similarly, oxidation of alkyl thiophenols also provided the
corresponding sulfones in high yields (entries 9, 15, 17 and
19). It is notable that the catalytic system tolerates a wide
variety of functional group. For example, methylthio
benzothiazole (11f) that is a useful nucleophile for the
Julia olefination was converted to the sulfone 13f in 78%
yield (entry 11). In this reaction, benzothiazole ring was
unaffected through the reaction. The chemoselective
oxidation of methylthiobenzaldehyde (11g) proceeded to
give 13g in 86% yield with intactness of formyl group (entry
1
9
regioselectivity (1.3/1–1.7/1) (entries 5–7). Turning to
cyclic secondary amines, tetrahydroisoquinoline (9i) was
converted to 10i, which is the useful substrate for the
synthesis of isoquinoline alkaloids, in 70% yield (entry
1
6c
9
).
instead of the corresponding nitrone.
Oxidation of tetrahydroquinoline (9j) provided 10j
1
6d
(entry 10). The
reaction of cyclic aliphatic amine 9k was so messy because
of the side reactions such as oxidative dimerization so that
the corresponding product was not isolated (entry 11).
2
3
5
. Oxidation of sulfides catalyzed by PWAA
13). Besides, the oxidation of 11h and 11i proceeded
Next, we turned our attention to oxidation of sulfides to
Sulfones have been utilized as the
syntons for total synthesis of bioactive natural compounds.
As depicted in parenthesis in Table 3, oxidation of 11a–k
with hydrogen peroxide in the absence of PWAA proceeded
sluggishly to give mainly the corresponding sulfoxides
efficiently to give 13h and 13i in high yields, where the
olefin and alcohol were tolerated and b-elimination of the
alcohol was not observed (entries 15 and 17). Sulfide 11j
with a cyclic acetal in the structure was converted to 13j,
which was the substrate for the preparation of the
prostaglandin analogue, in 71% yield (entry 19). On the
other hand, the reaction of diphenyl sulfide 11k hardly
proceeded (entry 21).
20,21
sulfones (Table 3).
2
4
Table 3. Oxidation of sulfides to sulfones with and without PWAA
The recycled activity of PWAA in the oxidation of sulfide
11a was evaluated (Scheme 7). The oxidation of 11a was
performed under identical conditions, affording 13a in 97%
yield. In the repeated use of the recovered catalyst, PWAA
mediated the second to fifth cycled runs to give 13a in
82–88% yields. The reason to reduce yields in the second
cycled run was unclear. One explanation for this may be that
PWAA was pulverized and adsorbed onto the reaction
vessel so that the efficiency of the reaction was reduced
physically. In this respect, It was confirmed that the
pulverization did not affect the intrinsic activity of
PWAA: the recovered PWAA was analyzed by gel-phase
a
a
Entry
11
PhSMe (11a)
11a
Catalyst
12 (%)
13 (%)
b
1
2
PWAA
—
PWAA
—
PWAA
—
PWAA
—
3
(74)
9
(71)
12
(70)
6
(76)
3
(75)
97
(26)
90
(22)
87
(15)
84
(24)
91
b
3
4
5
6
7
8
9
p-Me–C
11b
p-Br–C
11c
p-MeO–C
6
H
4
SMe (11b)
SMe (11c)
SMe (11d)
6
H
4
3
1
6
H
4
P NMR to show a broad peak at 213 ppm as well as the
2
PWAA before use.
5
11d
PhSEt (11e)
11e
PWAA
—
1
0
1
(17)
As stated above, all the reactions were performed under
organic solvent-free conditions. PWAA was insoluble and
stable in both aqueous and organic solvents. We expected
that PWAA should efficiently catalyze the oxidation in any
media. Hence, the activity of PWAA in an organic solvent
was investigated. The reactions of 11a to 13a were carried
out with various organic solvents as depicted in Table 4.
Similar to the oxidation without organic solvent completed
in 4 h to give 13a in 97% yield (entry 1), the reaction with
c
c
(11f)
1
PWAA
17
78
12
13
14
11f
p-CHO–C
11g
—
PWAA
—
(9)
—
(53)
(0)
86
(33)
6
H
4
SMe (11g)
c
c
(11h)
15
16
17
18
PWAA
—
3
81
(10)
11h
11i
(80)
—
(
11i)
PWAA
—
Quant
(13)
(80)
19
(11j)
PWAA
11
71
20
21
22
11j
PhSPh (11k)
11k
—
PWAA
—
(54)
10
4
(trace)
6
(0)
The yields of the oxidations without PWAA were in parentheses.
a
Isolated yields.
b
3
The reaction was performed for 7 h.
mol equiv. of H
2 2
O was used.
c
Scheme 7. Oxidation of 11a catalyzed by recycled PWAA.

Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
4093
Table 4. Solvent effect on the oxidation catalyzed by PWAA
was added C H Br (2.92 mL; 12.1 mmol), and it was
12 25
stirred at 60 8C for 48 h before it was filtered. The filtrate
was evaporated, and purified by column chromatography
(neutral silica gel; eluent: CH Cl /MeOH (gradient: 10/1–
2 2
2/1 via 5/1) to afford 4 in 92% yield (2.27 g). Mp 57–70 8C;
IR (KBr, cm ): 1628, 1670, 3443; H NMR (400 MHz,
2
1
1
a
a
Entry
Solvent
12a
13a
CDCl ): d 0.88 (t, J¼7.1 Hz, 3H), 1.22–1.35 (m, 18H), 1.74
3
1
2
3
4
5
6
7
(Neat)
Toluene
3
3
8
97
75
90
91
96
(m, 2H), 2.16 (m, 2H), 3.27 (s, 6H), 3.35–3.40 (m, 2H),
3
6
8
.47–3.49 (m, 2H), 3.87 (m, 2H), 5.63 (d, J¼11.5 Hz, 1H),
CH
THF
Et
2
Cl
2
.33 (d, J¼17.1 Hz, 1H), 6.54 (dd, J¼11.5, 17.1 Hz, 1H),
8
1
3
.55 (br s, 1H); C NMR (100 MHz, CDCl ): d 14.2, 22.7,
3
2
O
—
—
—
DMF
EtOH
100
99
22.7, 22.9, 26.4, 29.2, 29.3, 29.4, 29.5, 29.6, 31.9, 36.4,
51.0, 62.9, 64.9. 126.5, 130.7, 166.40; MS (FAB): m/z 326
þ
26.3297, found 326.3300.
a
(M þH, base peak); HRMS (FAB): calcd for C H ON
20 42
Isolated yields.
2
3
aprotic hydrophobic solvents (toluene, CH Cl , THF, and
2
2
Et O (entries 2–5)), hydrophilic solvent (DMF (entry 6)),
2
7.1.2. Poly{[3-(acryloylamino)propyl]dodecyldimethyl-
ammonium bromide}-co-(N-isopropylacrylamide) }
and protic solvent (EtOH (entry 7)) progressed smoothly to
furnish 13a in high yields. On the contrary, the reaction in
toluene proceeded slower to give 13a in 75%. It seems
reasonable that both organic solvent-free and -containing
systems were effective for this oxidation.
1
2
(6). The solution of 4 (1.46 g; 3.60 mmol), N-isopropyl-
acrylamide (4.89 g; 43.2 mmol) in t-BuOH (70 mL) was
degassed by ultrasonication for 20 min under an argon
atmosphere. After AIBN (23.7 mg; 0.144 mmol) was added
and again degassed for 20 min, the solution was heated at
75 8C for 48 h under an argon atmosphere, and t-BuOH was
evaporated. The residue was purified by sedimentation from
6
. Summary
2
1
CH Cl and Et O to give 6 in 86% (5.44 g). IR (KBr, cm ):
2
2
2
1
In conclusion, we developed a highly active and reusable
solid-phase catalyst, PWAA based on our strategy: the self-
assembly of phosphotungstate and an ammonium salt with a
non-cross-linked amphiphilic polymer. PWAA efficiently
catalyzed the oxidations of allylic alcohols, amines, and
sulfides with hydrogen peroxide in both aqueous and
organic media. PWAA was reused three to five times and
the turnover number of PWAA reached up to 35,000. While
the reusable activity and stability of PWAA should be
improved, we believe our concept will be useful for creating
1651, 3069, 3308; H NMR (600 MHz, CDCl
): d 0.88 (t,
3
J¼9.6 Hz, 3H), 0.90–2.60 (m, 133H), 3.19–4.10 (m, 24H),
1
3
6.64 (br s, 13H); C NMR (150 MHz, CDCl
26.1, 29.0, 29.2, 29.3, 31.6, 41.1, 42.1, 50.5, 174.2.
Elementary anal. calcd for C92n as
6·7nH O: C 58.5, H 10.0, N 10.4, found: C 58.8, H 10.3,
N 10.3.
): d 13.8, 22.4,
3
H
N O20nBr
187n 14n n
2
7.1.3. Poly{[3-(acryloylamino)propyl]dodecyldimethyl-
ammonium nitrate}-co-(N-isopropylacrylamide)12} (2).
The mixture of 6 (1.72 g) and 0.2 M aqueous NaNO was
3
4
other solid-phase catalysts.
vigorously stirred for 41 h, followed by heated at 60 8C to
precipitate 2, and supernatant was decanted. The residue
7
. Experimental
was washed with H
2
O, and dried in vacuo (,0.08 mmHg) to
give 2b in 81% yield (1.38 g). IR (KBr, cm ): 1651, 3065,
21
1
7
.1. General
5–40% Hydrogen peroxide and H PW O were used
3298; H NMR (600 NMR, CDCl
3H), 0.90–2.60 (m, 133H), 3.20–4.10 (m, 24H), 6.61 (br s,
13H); C NMR (150 MHz, CDCl ): d 14.0, 22.5, 22.6,
3
): d 0.88 (t, J¼9.6 Hz,
1
3
3
3
3
12 40
without any treatment Infrared (IR) spectra were recorded
on a JASCO FT/IR-8000 Fourier transform infrared
spectrophotometer. NMR spectra were recorded on a
26.4, 29.2, 29.4, 29.5, 31.8, 41.2, 42.2, 50.4, 174.3.
Elementary anal. calcd for
2·7nH O: C 59.0, H 10.1, N 11.2, found: C 59.3, H 10.3,
N 11.4.
C
H N O23n as
92n 187n 15n
2
1
JEOL AL-400 spectrometer, opening at 400 MHz for H
1
3
NMR and 100 MHz for C NMR. Chemical shifts in CDCl3
were reported in the d scale relative to CHCl (7.26 ppm for
7.1.4. Preparation of an assembled catalyst PWAA (3)
from 1 with 2. When an aqueous solution of 1 (334 mg in
3
1
13
H NMR and 77.00 ppm for C NMR) as an internal
3
1
reference. Gel-phase P NMR spectra were recorded with a
1
33 mL of H
was added to an aqueous solution of 2 (608 mg in 116 mL
O; 3 mol equiv. as an ammonium unit) at room
2 2
O; 1 was dissolved in H O by ultrasonication.)
6
00 MHz ( H NMR) pulse Fourier transform NMR
spectrometers in CDCl3 suspension with 85% H PO
H
3
4
2
aqueous solution as an external standard. EIMS spectra
were measured on JEOL SX-102A. Column chromato-
graphy was performed with silica gel Merck 60 (230–400
mesh ASTM).
temperature, white insoluble precipitates were simul-
taneously yielded. After being stirred for 7 days at the
same temperature, the precipitate was filtered on a glass
filter, washed thoroughly with water, and dried in vacuo
(
white lumps: IR (KBr, cm ) 1080, 982, 893, 808; gel-
,0.08 mmHg) to give 3 in 95% yield (870 mg) as
21
7.1.1. [3-(Acryloylamino)propyl]dodecyldimethylammo-
nium bromide (4). To the suspension of N-[3-(dimethyl-
3
1
phase P NMR d 213 (br s). Elementary anal. calcd for
12n as PWAA·22nH O: C 39.8, H
6.3, N 7.1, found: C39.6, H 6.6, N 7.2.
amino)propyl]acrylamide (1.0 mL; 6.07 mmol), Na CO
2
C
276n
H
563n
N
42n
O
101n
P
n
W
2
3
(
0.161 g; 1.52 mmol) in MeOH and MeCN (12 mL each)

4094
Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
7.2. General procedure for assembled catalyst-promoted
epoxidation of allylic alcohols with hydrogen peroxide
123.1, 125.4, 125.4, 125.4, 125.5, 125.8, 128.5, 129.1,
þ
129.5, 132.2, 144.6, 158.9; MS (EI): m/z 295 (M ), 159
þ þ
M 2NHCH ArOCH ), 121 (M 2NHCH ArOCF , base
2 3 2 3
(
A 25-mL flask equipped with a magnetic stirring bar was
charged with 2.52 mmol of 7a, 5.05 mmol of 30% aqueous.
H O and 1.26 mmol of PWAA. After the mixture was
peak); HRMS (EI): calcd for C H ONF 295.1184, found
16 16 3
295.1180.
2
2
stirred at room temperature for 7 h, toluene (or Et O, AcOEt
2
7.3.3. N-(Z)-4-Methoxybenzyl-N-4-(trifluoromethyl)-
benzylidene N-oxide (10e). Mp 124–129 8C; IR (KBr,
cm ): 1327, 3072 cm; H NMR (400 MHz, CDCl ): d 3.82
3
could be used.) was added, and PWAA was filtered. The
organic layer was separated, washed with saturated aqueous.
Na S O , dried in vacuo, and purified by flash column
2
1
1
(s, 3H), 5.02 (s, CH OArCH N(O)vCHArCF , 2H), 6.93–
3
2
2
3
3
2
chromatography (SiO ; EtOAc/hexane¼1:4 to 1:2) to give
6.96 (m, 2H), 7.39–7.41 (m, 3H), 7.63 (d, J¼8.3 Hz, 2H),
2
1
3
the epoxy alcohol 8a in 96% isolated yield.
8.30 (d, J¼8.3 Hz, 2H); C NMR (100 MHz, CDCl ): d
3
55.4, 71.1, 114.4, 122.3, 124.6, 125.0, 125.1, 125.2, 128.4,
130.8, 131.1, 131.5, 132.2, 133.4, 160.1; MS (EI): m/z 309
7
Colorless oil; IR (neat, cm ) 3406, 2932, 1454, 1032,
.2.1. 2,3-Epoxy-3-methyl-5-phenyl-1-pentanol (8e).
2
1
þ
(EI): calcd for C H O NF 309.0977, found 309.0971.
þ
(M ), 121 (M 2N(O) vCHArCF , base peak); HRMS
3
1
7
1
2
52, 702; H NMR (400 MHz, CDCl ): d 1.34 (s, 3H),
3
16 14
2
3
.72–1.80 (m, 1H), 1.94–2.01 (m, 1H), 2.32 (br s, 1H),
.64–2.79 (m, 2H), 2.88 (dd, 1H, J¼4.2, 6.6 Hz), 3.63 (br
7.3.4. N-(Z)-4-Methoxybenzylidene-N-4-(trifluoro-
methyl)benzyl N-oxide (10e ). Mp 124–128 8C; IR (KBr,
0
cm ): 1327, 3082; H NMR (400 MHz, CDCl ): d 3.84 (s,
dd, 1H, J¼6.6, 11.6 Hz), 3.73 (br dd, 1H, J¼4.2, 11.6 Hz),
1
3
21
1
7
3
1
.15–7.29 (m, 5H); C NMR (100 MHz, CDCl ) d 16.9,
3
3
1.3, 40.3, 60.9, 61.3, 63.0, 125.9, 128.1, 128.3, 128.4,
þ
3H), 5.07 (s, CH OArCHvN(O)CH ArCF , 2H), 6.93 (d,
3
2
3
41.0; MS (EI): m/z 192 (M ), 174, 143, 131, 117, 105, 91;
J¼8.8 Hz, 2H), 7.42 (s, CH OArCHvN(O)CH ArCF ,
3
2
3
HRMS (EI): calcd for C H O 192.1150, found 192.1159.
12 16 2
1H), 7.61 (d, J¼8.3 Hz, 2H), 7.66 (d, J¼8.3 Hz, 2H), 8.22
1
3
(
d, J¼8.8 Hz, 2H); C NMR (100 MHz NMR, CDCl ): d
3
7.3. General procedure for the oxidation of amines
catalyzed by PWAA
55.4, 70.0, 113.8, 123.0, 125.6, 125.7, 129.1, 130.5, 131.0,
134.2, 137.2, 161.1; MS (EI): m/z 309 (M ), 159 (M 2
þ
N(O)vCHArOCH , base peak); HRMS (EI): calcd for
þ
3
2
3
To a suspension of PWAA (40 mg; 5£10 mmol) and 9a
C H O NF 309.0977, found 309.0978.
1
6
14
2
3
(
(
2.52 mmol) was added 2.5% H O aqueous solution
2 2
7.56 mmol) dropwise for 50 min at 0 8C. The mixture
7.3.5. N-(Z)-4-Benzyl-N-4-nitrilebenzylidene N-oxide
(10g). Mp 143–150 8C; IR (KBr, cm2 ): 2224, 3034; H
1
1
was stirred at room temperature for 24 h, before it was
diluted with AcOEt and filtered through a glass filter. Brine
was added to the filtrate, and it was extracted with AcOEt
NMR (400 MHz, CDCl3): 5.09 (s, ArCH2-
d
N(O)vCHArCN, 2H), 7.40–7.49 (m, ArCH2N(O)v
CHArCN, 6H), 7.66 (d, J¼8.6 Hz, 2H), 8.29 (d,
(
Na SO , filtered, dried in vacuo, and purified by column
£3). The extract was washed with brine, dried over
1
3
J¼8.6 Hz, 2H); C NMR (100 MHz, CDCl ): d 71.9,
2
4
3
chromatography (SiO ; EtOAc/hexane¼1:5) to give 10a in
112.9, 118.4, 128.3, 129.0, 129.2, 132.0, 132.3, 132.4,
134.0; MS (EI): m/z 236 (M ), 91 (M 2N(O)vCHArCN,
2
þ
base peak); HRMS (EI): calcd for C H ON 236.0950,
þ
8
6% yield.
1
5
12
2
0
N-oxide (10d). Mp 122–125 8C; IR (KBr, cm ): 1246,
7
.3.1. N-((Z)-4-Methoxybenzylidene-4 -methoxybenzyl)
2
found 236.0947.
1
1
2
3
7
920 cm; H NMR (400 MHz, CDCl ): d 3.81 (s, 3H),
3
7.3.6. N-(Z)-4-Benzylidene-N-4-nitrilebenzyl N-oxide
21
0
1
.82, (s, 3H), 4.95 (s, 2H), 6.88–6.94 (m, 4H), 7.26 (s, 1H),
3
(10g ). Mp 140–144 8C; IR (KBr, cm ): 2224, 3034; H
NMR (400 MHz, CDCl ): d 5.11 (s, ArCHvN(O)CH -
1
.37–7.41 (m, 2H), 8.17–8.21 (m, 2H);
C NMR
3
2
(
100 MHz, CDCl ): d 55.3, 55.3, 70.1, 113.6, 114.2,
3
ArCN, 2H), 7.39–7.44 (m, 3H), 7.51 (s, ArCHvN(O)-
CH2ArCN, 1H), 8.29 (d, J¼8.6 Hz, 2H), 8.21–8.24 (m,
123.3, 125.3, 130.4, 130.6, 133.2, 159.8, 160.8; MS (EI):
m/z 271 (M ), 121 (M 2N(O)vCHArOMe, base peak);
þ
HRMS (EI): calcd for C H O N 271.1208, found
þ
13
2H); C NMR (100 MHz, CDCl3): d 70.1, 112.4, 117.9,
128.1, 128.2, 129.0, 129.6, 130.4, 132.1, 134.5, 137.9; MS
1
6 17 3
þ
HRMS (EI): calcd for C H ON 236.0950, found
þ
2
71.1205.
(EI): m/z 236 (M ), 116 (M 2N(O)vCHAr, base peak);
1
5
12
2
7
.3.2. N-4-Methoxybenzyl-N-4-trifluoromethylbenzyl-
236.0944.
amine (9e). To a solution of 5% Pd/C (80 mg) in methanol
27 mL) under H atmosphere was added 4-trifluoromethyl-
benzaldehyde (1.23 mL; 9 mmol) and 4-methoxybenzalde-
hyde (1.08 mL; 9.9 mmol), and the resulting mixture was
stirred at rt for 5 h. After the substrate was consumed
(
7.4. General procedure for the oxidation of sulfides to
sulfones catalyzed by PWAA
2
The mixture of PWAA, 11a and 35–40% H O aqueous
2
2
(
checked by TLC), the suspension was filtered. The filtrate
was evaporated, purified by column chromatography (SiO2;
solution was shaken by PetiSytherw (Shimadzu Scientific
Research Inc. Japan) at 700 rpm at 50 8C for 4 h, it was
diluted with AcOEt and filtered. To the filtrate was added
saturated Na S O and brine, and it was extracted with
MeOH/CH Cl ¼1:100) to give 9e in 72% yield (1.73 g;
2
2
2
1
1
6.50 mmol). Mp 29–30 8C; IR (neat, cm ): 1327, 3337; H
NMR (400 MHz, CDCl ): d 1.73 (br s, 1H), 3.73 (s, 2H),
2
2 3
AcOEt (£3), dried over Na SO , filtered, dried in vacuo, and
3
2
4
3
.79 (s, 3H), 3.84 (s, 2H), 6.87 (d, J¼8.5 Hz, 2H), 7.25 (d,
purified by column chromatography (SiO ; MeOH/
2
J¼8.5 Hz, 2H), 7.45 (d, J¼8.1 Hz, 2H), 7.57 (d, J¼8.1 Hz,
CH Cl ¼1:100) to give 13a in 97% yield. While the shaker
2
2
1
3
w
2
H); C NMR (100 MHz, CDCl ) d 52.8, 52.9, 55.6, 114.1,
3
(PetiSyther ) for solid-phase syntheses was used in these

Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
4095
reactions, the glassware vessel equipped with a magnetic
stirrer enabled to be also used.
ammonium salt units in 2 was essential for cross-linking the
polymers through phosphotungstates.
9
. Massart, R.; Contant, R.; Fruchart, J.-M.; Ciabrini, J.-P.;
Fournier, M. Inorg. Chem. 1977, 16, 2916–2921.
1
0. Ishii, Y.; Tanaka, H.; Nishiyama, Y. Chem. Lett. 1994, 1–4.
1. (a) Keggin, J. F.; Proc, R. Proc. R. Soc. London, Ser. A 1934,
Acknowledgements
1
1
44, 75–100. (b) Brown, G. M.; Noe-Spirlet, M.-R.; Busing,
We thank Ms. Junko Shimode and Ms. Maroka Kitsukawa
Teikyo University) for spectroscopic measurement, and
W. R.; Levy, H. A. Acta Crystallogr. B 1977, 33, 1038–1046.
2. (a) For examples of the epoxidation by homogeneous tungsten
catalysts, see:Ogata, Y.; Sawaki, Y. In Organic syntheses by
oxidation with metal compounds; Mijs, W. J., De Jonge, C. R.
H. I., Eds.; Plenum Press: New York, 1986; pp 839–876.
(
1
Mr. Kiyoshi Abe (Teikyo University) and Mr. Shin-ichirou
Kawabata (JEOL Ltd) for SEM measurement. This work
was partially supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Science and
Technology. Y.M.A.Y. thanks the Inoue Foundation for
Science (IFS) for Inoue Research Award for Young
Scientists, and Dainippon Ink and Chemicals, Inc. Award
in Synthetic Organic Chemistry, Japan.
(
b) Sato, K.; Aoki, M.; Noyori, R. Science 1998, 281,
646–1647. (c) Venturello, C.; Gambaro, M. J. Org. Chem.
991, 56, 5924–5931. (d) Venturello, C.; Gambaro, M.
1
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Synthesis 1989, 295–297. (e) Bortolini, O.; Conte, V.; Di
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2
661–2663.
1
3. (a) Recent attempts to improve the drawbacks on polymer-
supported tungsten catalysts for the epoxidation, see: Villa,
A. L.; Sels, B. F.; De Vos, D. E.; Jacobs, P. A. J. Org. Chem.
1999, 64, 7267–7270. (b) Hoegaerts, D.; Sels, B. F.; de Vos,
D. E.; Verpoort, F.; Jacobs, P. A. Catal. Today 2000, 60,
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14. It was reported that pH control in aqueous media was
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002, 102, 3837–3892.
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. (a) Yamada, Y. M. A.; Ichinohe, M.; Takahashi, H.; Ikegami,
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002, 43, 3431–3434. (c) Yamada, Y. M. A.; Takeda, K.;
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(
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(
S. Synlett 2002, 2031–2034.
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5
6
. Partial results were reported as communications, see Refs. 4a
and 4d.
. Jacobs and co-workers reported the Amberlite IRA-900-
supported Venturello catalyst converted into NO3- was
effective for the enhancement of selectivity of epoxidation,
see: Villa, A. L.; Sels, B. F.; de Vos, D. E.; Jacobs, P. A. J. Org.
Chem. 1999, 64, 7267–7270.
7
8
. Ishii, Y.; Yamawaki, K.; Ura, T.; Yamada, H.; Yoshida, T.;
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. Addition of 1 to poly(N-isopropylacrylamide) afforded no
precipitates. This result indicated that the existence of the
2 2
18. The reaction oxidized by more concentrated H O aqueous
solution was less successful because dimerization of the
substrates occurred. Besides, recycling of PWAA in case of 9a
was not efficient to afford 10a in lower yield.

4096
Y. M. A. Yamada et al. / Tetrahedron 60 (2004) 4087–4096
1
9. These oxidations were controlled kinetically, and the regio-
selectivity for the formation of nitrones was determined at the
oxidation stage of dibenzyl hydroxyamines to nitrones. It was
assured by the following results: no isomerization between 10e
21. (a) For recent developments and improvements for the
oxidation of sulfides to sulfones, see: (a) Dell’Anna, M. M.;
Mastrorilli, P.; Nobile, C. F. J. Mol. Catal. A: Chem. 1996,
108, 57–62. (b) Alcon, M. J.; Corma, A.; Iglesias, M.;
Sanchez, F. J. Mol. Catal. A: Chem. 2002, 178, 253–266.
22. Noyori et al. reported that the oxidation of sulfides to
sulfoxides proceeded efficiently in hydrogen peroxide without
catalysts, so that we have not examined the selective oxidation
to sulfoxide. See Ref. 19g.
0
0
and 10e was observed in the reaction of 10e or 10e in the
presence of PWAA and 2.5% H
CH Cl at room temperature provided 10e and 10e in 95%
2
O
2
; the reaction of 9e in
0
2
2
0
yield with the same regioselectivity (10e/10e ¼1.76/1); even
0
in the reaction of 10e or 10e with CH
conditions, isomerizations were hardly observed.
2
Cl
2
under identical
23. Baudin, J. B.; Hareau, G.; Julia, S. A.; Ruel, O. Tetrahedron
Lett. 1991, 32, 1175–1178.
2
0. (a) For examples of the oxidation of sulfides to sulfones by
homogeneous tungsten catalysts, see: (a) Schultz, H. S.;
Freyermuth, H. B.; Buc, S. R. J. Org. Chem. 1963, 28,
24. (a) Kondo, K.; Tunemoto, D. Tetrahedron Lett. 1975, 17,
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G. Polish J. Chem. 1996, 70, 1121–1123. (c) Neumann, R.;
Juwiler, D. Tetrahedron 1996, 52, 8781–8788. (d) Gresley,
N. M.; Griffith, W. P.; Laemmel, A. C.; Nogueira, H. I. S.;
Perkin, B. C. J. Mol. Catal. 1997, 117, 185–198. (e) Collins,
F. M.; Lucy, A. R.; Sharp, C. J. Mol. Catal. 1997, 117,
25. Br e´ gault et al. reported that heteropoly acidic structure easily
decomposed in the presence of hydrogen peroxide under the
homogeneous conditions, see: Salles, L.; Aubry, C.;
Thouvenot, R.; Robert, F.; Dor e´ mieux-Morin, C.; Chottard,
G.; Ledon, H.; Jeannin, Y.; Br e´ gault, J. Inorg. Chem. 1994, 33,
871–878On the other hand, Ishii et al. proved that [p-C H -
3
97–403. (f) Yasuhara, Y.; Yamaguchi, S.; Ichihara, J.;
Nomoto, T.; Sasaki, Y. Phosphorus Res. Bull. 2000, 11,
3–46. (g) Sato, K.; Hyodo, M.; Aoki, M.; Zheng, X.-Q.;
Noyori, R. Tetrahedron 2001, 57, 2469–2476, Also, see: Ref. 9.
5
5
þ
32
2 3 3
N (CH )15CH ] PW12O40 maintained the structure closed to
4
Keggin unit after treatment with hydrogen peroxide. See Ref.
10.