Alternative, easy and efficient preparation of poly[4-(diacetoxyiodo) styrene] from poly(4-iodostyrene) using sodium perborate as the oxidant

Article abstract of DOI:10.1055/s-2006-926402

An operationally simple, efficient, and considerably improved preparative procedure of poly[4-(diacetoxyiodo)styrene] (PSDIB) is reported. This procedure is performed with acetic acid, 1,2-dichloroethane, commercially available sodium perborate tetrahydrate as an oxidant, and triflic acid as an additive, and gives PSDIB after a short reaction time. PSDIB is employed as an oxidiz-ing agent in organic synthesis and can be regenerated and reused in the same reaction. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926402

PAPER
1253
Alternative, Easy and Efficient Preparation of Poly[4-(diacetoxyiodo)styrene]
from Poly(4-iodostyrene) Using Sodium Perborate as the Oxidant
P
M
reparationof
P
oly[4-
(
d
diacetoxyiod
.
o)styrene]
f
D
rom Poly(4-iodosty
e
rene) lwar Hossain, Tsugio Kitamura*
Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502,
Japan
Fax +81(952)288548; E-mail: kitamura@cc.saga-u.ac.jp
Received 8 November 2005; revised 8 December 2005
peptide-supported (diacetoxyiodo)benzene from Merri-
Abstract: An operationally simple, efficient, and considerably im-
field’s peptide resin.
proved preparative procedure of poly[4-(diacetoxyiodo)styrene]
(
1
PSDIB) is reported. This procedure is performed with acetic acid, The standard and most general method for the synthesis of
,2-dichloroethane, commercially available sodium perborate tet-
PSDIB is the oxidative diacetoxylation of poly(4-iodosty-
rahydrate as an oxidant, and triflic acid as an additive, and gives
PSDIB after a short reaction time. PSDIB is employed as an oxidiz-
ing agent in organic synthesis and can be regenerated and reused in
the same reaction.
4a,5s,6
rene) by peracetic acid at room temperature or 48 °C,
however, it requires prolonged reaction times (15–24 h).
Aminomethylated polystyrene is an inexpensive and com-
mercially available prefunctionalized polymer for the
preparation of aminomethylpolystyrene-supported (diacet-
Key words: poly[4-(diacetoxyiodo)styrene], sodium perborate, tri-
flic acid, oxidation, hypervalent iodine
7
oxyiodo)benzene, which should be protected from direct
sunlight and can be stored in a refrigerator although no ap-
preciable decomposition was observed at room tempera-
ture. The activity of Merrifield’s peptide-supported
In the last 20 years, hypervalent iodine reagents have en-
joyed an increase in popularity in organic synthesis. They
1
(
diacetoxyiodo)benzene was found to be 1.4 mmol/g.8
were used for a wide range of chemical transformations,
The oxidation of Hantzsch 1,4-dihydropyridines with
Merrifield’s peptide-supported (diacetoxyiodo)benzene
afforded good yields but the presence of electron-with-
drawing groups such as a nitro group retarded the oxida-
tion. In order to circumvent these problems we envisaged
an alternative method for the preparation of PSDIB from
poly(4-iodostyrene) using sodium perborate.9
2
especially as reagents for oxidations. The advantages of
hypervalent iodine reagents are the simple experimental
operation and low toxicity of the reagents. Several poly-
3
mer-bound oxidants have been reported, and polymer-
supported hypervalent iodine reagents should be a wel-
come addition due to their versatility, low toxicity, and
high reactivity. Among hypervalent iodine compounds,
In our laboratory, we found a quick (4 h) and efficient
method for preparing PSDIB from the corresponding
poly(4-iodostyrene) in acetic acid and 1,2-dichloroethane
using commercial sodium perborate as an oxidant and tri-
flic acid as an additive at 44–45 °C (Scheme 1). After fil-
tration, PSDIB was washed with diethyl ether and dried.
Poly(4-iodostyrene) was prepared by the reaction of poly-
styrene with iodine, iodine pentoxide, carbon tetrachlo-
ride, and sulfuric acid (50%) in nitrobenzene at 90 °C for
(
diacetoxyiodo)benzene has attracted significant interest,
while poly[4-(diacetoxyiodo)styrene] (PSDIB) is expect-
ed to have the same reactivity as (diacetoxyiodo)ben-
zene. Hitherto, PSDIB has found application in many
reactions, such as the preparation of phenylpolystyryl io-
donium bisulfate, 3,4-dihydro-2,1-benzothiazine 2,2-di-
oxides, 2,5-disubstituted oxazoles, 5–7 membered cyclic
ethers, and methyl carbamates. It has also been applied to
the oxidation of amines and alcohols, iodination of aro-
matic compounds, and the oxidative 1,2-aryl migration of
4
7
2 hours.5d The oxidizing ability of sodium perborate is
much improved by addition of triflic acid. Triflic acid is
5
alkyl aryl ketones. The major advantage of polymer-
10
3
0 times stronger than concentrated sulfuric acid, while
bound reagents is that the polymeric reagents can be re-
generated and reused as an environmentally benign re-
agent. Preparation of the polymeric version of the
iodine(III) reagent as a form of polymer-supported (di-
acetoxyiodo)benzene was reported by several research
groups. For example, Okawara et al. showed that PSDIB
could be prepared by iodination of polystyrene followed
by peracetic acid oxidation; Giannis et al. reported the
preparation of aminomethylpolystyrene-supported (diacet-
the thermal stability of triflic acid is far superior to that of
other acids.11 Sodium perborate, a stable, colorless, and
crystalline solid, is used as a strong oxidizing agent in
many applications and has the advantages of being very
12
6
cheap, safe, non-toxic, and easy to handle. The polymer
loading of PSDIB in terms of the (diacetoxyiodo)phenyl
13
7
group was determined by iodometric titration to be 1.86
mmol/g. When triflic acid was replaced with concentrated
sulfuric acid, the activity of PSDIB was not improved.
8
oxyiodo)benzene; Ko et al. synthesized Merrifield’s
In order to test their activity, benzyl alcohol was convert-
ed to benzaldehyde, after a short reaction time, with a de-
fined quantity of PSDIB. The yield of benzaldehyde
SYNTHESIS 2006, No. 8, pp 1253–1256
x
x
.
x
x
.2
0
0
6
Advanced online publication: 27.03.2006
DOI: 10.1055/s-2006-926402; Art ID: F19205SS
Georg Thieme Verlag Stuttgart · New York
(Table 1) was about the same as that reported in the liter-
©

1
254
Md. D. Hossain, T. Kitamura
PAPER
shifts are expressed in ppm downfield from TMS. IR spectra were
recorded on a Perkin Elmer FT-IR spectrometer Spectrum 2000.
Polystyrene was purchased from Aldrich (33165-1).
I2, I2O5, CCl4
n
n
5
0% H2SO4, PhNO2
Poly(4-iodostyrene)5d
90 °C, 72 h
A mixture of polystyrene (5 g, 47.81 mmol), I (5.62 g, 22.19
2
I
mmol), I O (2.19 g, 6.56 mmol), CCl (12.5 mL), H SO (50%,
2
5
4
2
4
1
0.9 mL), and nitrobenzene (62.5 mL) was kept at 90 °C for 72 h.
After the reaction was complete, the reaction mixture was diluted
n
NaBO3⋅4H2O, CF3SO3H
n
with CHCl (32 mL), then MeOH (469 mL) was added, and a pre-
3
cipitate formed. The precipitate was collected by filtration; yield:
AcOH, C2H4Cl2
5
.80 g.
44–45 °C, 4 h
IR (KBr): 3050, 3023, 2919, 2749, 1524, 1482, 1003, 818, 757, 699,
I
I(OAc)2
PSDIB
–
1
5
38 cm .
PSDIB
Scheme 1 Synthesis of PSDIB from polystyrene
A solution of poly(4-iodostyrene) (0.231 g), AcOH (5 mL), DCE (7
mL), and TfOH (6 mmol) was heated with stirring at 44–45 °C.
Then, NaBO ·4H O (6 mmol) was added slowly portionwise over
5
f
ature. Subsequently, several other substrates, 1-phenyl-
ethanol, benzamide, cyclohexanecarboxamide, and
propiophenone, were converted to acetophenone, methyl
N-phenylcarbamate, methyl N-cyclohexylcarbamate, and
methyl 2-phenylpropionate, respectively, with short reac- yield: 0.275 g.
3
2
1
0 min and stirring was continued for 4 h. The solution was then
concentrated by evaporation of DCE and AcOH under reduced
pressure. H O (10 mL) was added, the precipitate was collected by
2
filtration, washed with H O (10 mL), Et O (20 mL), and dried;
2
2
5
f–h
tion times in excellent yields (Table 1).
A large-scale synthesis of PSDIB was conducted in a similar man-
ner. A solution of poly(4-iodostyrene) (1.38 g) in a mixture of
AcOH (30 mL), DCE (50 mL), and TfOH (36 mmol) was heated at
We also studied the regeneration and recycling of used
PSDIB. After the first run, the polymer was recovered by
filtration, washed with methanol, and the recovered poly-
mer was then reoxidized with sodium perborate in the
usual manner. The activity of the regenerated PSDIB was
found to be 1.63 mmol/g by iodometric titration. Oxida-
tion of 1-phenylethanol with the regenerated PSDIB un-
der the same conditions gave acetophenone in 90% yield.
4
4–45 °C with stirring. Then, NaBO ·4H O (36 mmol) was added
3 2
portionwise over 20 min and stirring was continued for 4 h. Work-
up as above gave PSDIB; yield: 1.62 g.
IR (KBr): 3055, 3018, 2923, 2848, 1628 (br), 1581 (br), 1483, 1450,
–
1
1
406, 1274, 1172, 1029, 1005, 819, 762, 702, 640, 540 cm .
Iodometric Titration13
Deionized H O (12.5 mL), H SO (6 N, 1.25 mL), KI (0.250 g),
2
2
4
In conclusion, we successfully improved the procedure
for the preparation of PSDIB by using poly(4-iodosty-
rene), acetic acid, dichloroethane, and triflic acid in the
presence of sodium perborate at 44–45 °C within short re-
CHCl (1.25 mL), and finally the prepared PSDIB (0.0310 g) were
3
placed in a 100-mL round-bottom flask, the mixture was stirred for
4
h, and then titrated against Na S O (0.1 N). The polymer loading
2 2 3
of the (diacetoxyiodo)phenyl group was calculated to be 1.86
action times. The product, PSDIB, is highly reactive and mmol/g.
can serve as an improved and recyclable oxidant for mod-
Oxidation of Alcohols with PSDIB; General Procedure
ern organic synthesis, particularly in combinatorial chem-
istry.
PSDIB (0.64 g, 1.2 mmol) was added to a solution of alcohol (1
mmol) and TEMPO (31 mg, 0.2 mmol) in acetone (3 mL) and the
mixture was stirred at r.t. for the time given in Table 1. At the end
Melting points were determined on a Yanaco micro-melting point
apparatus and are uncorrected. H NMR and C NMR spectra were
recorded on a JEOL JNM-AL300 spectrometer and the chemical
of the reaction, Et
tered to remove the polymer. After removal of the solvent, the fil-
trate was poured into H O (10 mL), and extracted with Et O (3 × 10
2
O (10 mL) was added and the mixture was fil-
1
13
2
2
Table 1 Oxidation of Alcohols, Carboxamides, and Propiophenone Using PSDIB
Entry
Reagent
Product
Time (h)
Yield (%)
1
2
3
4
Benzyl alcohol
1-Phenylethanol
Benzamide
Benzaldehydea
2
85
95
90
82
80
Acetophenonea
8
Methy N-phenylcarbamateb
Methyl N-cyclohexylcarbamateb
Methyl 2-phenylpropionatec
4
Cyclohexanecarboxamide
Propiophenone
4
5
10 min
a
Alcohol (1 mmol), TEMPO (31 mg, 0.2 mmol), Me CO (3 mL), PSDIB (0.64 g, 1.2 mmol), r.t.
2
b
c
KOH (2.5 equiv), MeOH (10 mL), carboxamide (1 equiv), PSDIB (0.54 g, 1 equiv), 5–10 °C to r.t.
H SO (2 mmol), propiophenone (1 mmol), HC(OMe) (3 mL), PSDIB (0.64 g,1.2 mmol), 60 °C.
2
4
3
Synthesis 2006, No. 8, 1253–1256 © Thieme Stuttgart · New York

PAPER
Preparation of Poly[4-(diacetoxyiodo)styrene] from Poly(4-iodostyrene)
1255
mL). The combined organic layer was dried (Na SO ), filtered, and References
2
4
the solvent was removed in vacuo. The residue was chromato-
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benzaldehyde and acetophenone, are commercially available com-
pounds, and the spectral data were in agreement with those from a
commercial source.
(
(
(
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1
1
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2
2
2
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2
2
4
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2
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Methyl N-Phenylcarbamate
Yield: 0.142 g (90%); mp 46–47 °C (Lit. mp 48–49 °C).
1
4
(4) (a) Togo, H.; Nogami, G.; Yokoyama, M. Synlett 1998, 534.
(
b) Ley, S. V.; Thomas, A. W.; Finch, H. J. Chem. Soc.,
1
H NMR (300 MHz, CDCl ): d = 3.76 (s, 3 H, OCH ), 6.80 (br s, 1
3
3
Perkin Trans. 1 1999, 669. (c) Ley, S. V.; Schucht, O.;
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H, NH), 7.05 (t, J = 8 Hz, 1 H, Ph) 7.29 (t, J = 8 Hz, 2 H, Ph), 7.37
(
d, J = 8 Hz, 2 H, Ph).
1999, 1251.
1
3
C NMR (75 MHz, CDCl ): d = 52.25, 118.74, 123.40, 128.96,
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3
1
37.82, 154.09.
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1
5
1
H NMR (300 MHz, CDCl ): d = 1.01–1.86 (m, 10 H, C H ), 3.38
3
6
11
(
br s, 1 H, C H ), 3.57 (s, 3 H, OCH ), 4.81 (br s, 1 H, NH).
6 11 3
1
3
C NMR (75 MHz, CDCl ): d = 24.63, 25.30, 33.20, 49.66, 51.52,
3
1
56.13.
(
i) Kawamura, Y.; Maruyama, M.; Tokuoka, T.; Tsukayama,
Methyl 2-Phenylpropionate5h
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2
4
(
0.64 g, 1.2 mmol) and propiophenone (1 mmol) in trimethylortho-
formate (3 mL) at r.t. The reaction mixture was stirred at 60 °C for
0 min, quenched with H O (10 mL), and extracted with Et O
1
2
2
(
3 × 10 mL). The combined organic layer was dried (Na SO ), fil-
2
4
tered, and the solvent was removed in vacuo. The residue was
chromatographed (silica gel) to give the pure methyl 2-phenyl-
propionate.
2
004, 392. (o) Cheng, D.; Chen, Z.; Zheng, Q. Synth.
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Yield: 0.142 g (80%).
(
r) Tohma, H.; Takizawa, S.; Maegawa, T.; Kita, Y. Angew.
1
H NMR (300 MHz, CDCl ): d = 1.49 (d, J = 7 Hz, 3 H, Me), 3.64
3
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(
s, 3 H, OMe), 3.72 (q, J = 7 Hz, 1 H, CHMe), 7.29 (s, 5 H, Ph).
1
3
C NMR (75 MHz, CDCl ): d = 18.53, 45.37, 51.92, 127.07,
3
1
27.41, 128.56, 140.52, 174.92,
2
005, 35, 1753. (v) Teduka, T.; Togo, H. Synlett 2005, 923.
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The authors are grateful to the Central Glass Co. for a generous gift
of triflic acid. This work was partly supported by a President’s
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1
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Synthesis 2006, No. 8, 1253–1256 © Thieme Stuttgart · New York

1
256
Md. D. Hossain, T. Kitamura
PAPER
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Synthesis 2006, No. 8, 1253–1256 © Thieme Stuttgart · New York