Dowex 50WX4-100: An efficient catalyst for the tetrahydropyranylation of alcohols

Article abstract of DOI:10.1080/00397910902774059

The ion-exchange resin Dowex 50WX4-100 has been found to catalyze efficiently the protection reaction of a variety of alcohols with 2,3-dihydro-4H pyran (DHP) and dichloromethane at ambient conditions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910902774059

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Dowex 50WX4–100: An
Efficient Catalyst for the
Tetrahydropyranylation of
Alcohols
a
a
a
P. S. Poon , Ajoy K. Banerjee , Liadis Bedoya
a
b
,
Manuel S. Laya , Elvia V. Cabrera & Karla M.
b
Albornoz
a
Chemistry Center, Venezuelan Institute of
Scientific Research (IVIC) , Caracas, Venezuela
b
Department of Chemistry , Faculty of Sciences,
University of Zulia , Maracaibo, Venezuela
Published online: 12 Aug 2009.
To cite this article: P. S. Poon , Ajoy K. Banerjee , Liadis Bedoya , Manuel S.
Laya , Elvia V. Cabrera & Karla M. Albornoz (2009) Dowex 50WX4–100: An Efficient
Catalyst for the Tetrahydropyranylation of Alcohols, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 39:18,
3369-3377, DOI: 10.1080/00397910902774059
To link to this article: http://dx.doi.org/10.1080/00397910902774059
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1
Synthetic Communications , 39: 3369–3377, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910902774059
Dowex 50WX4–100: An Efficient Catalyst
for the Tetrahydropyranylation of Alcohols
1
P. S. Poon, Ajoy K. Banerjee, Liadis Bedoya, Manuel S. Laya,
1
1
1
2
Elvia V. Cabrera, and Karla M. Albornoz
2
1
Chemistry Center, Venezuelan Institute of Scientific Research (IVIC),
Caracas, Venezuela
2
Department of Chemistry, Faculty of Sciences, University of Zulia,
Maracaibo, Venezuela
Abstract: The ion-exchange resin Dowex 50WX4–100 has been found to catalyze
efficiently the protection reaction of a variety of alcohols with 2,3-dihydro-4H
pyran (DHP) and dichloromethane at ambient conditions.
Keywords: Alcohols, reduction, tetrahydropyranylation, tetralones
INTRODUCTION
The protection of alcoholic hydroxyl groups has found application
especially in the synthesis of natural products related to terpenes,
steroids, sugars, and glycerids. Tetrahydropyranylation is one of the fre-
quently used methods for the protection of alcohols and phenols because
of the remarkable stability towards a variety of conditions such as reac-
tions involving Grignard reagents and lithium alkyl and reduction with
[
1,2]
hydrides, alkylating, and acylating agents.
been developed for tetrahydropyranylation of alcohols and phenols,
A variety of reagents have
[3]
[4]
which include mainly protic acids, Lewis acids, heterogeneous cata-
[
5]
[6]
lyst, and others. The use of ion-exchage resins in organic synthesis
[7]
has been reviewed by Gelbard. Amberlyst H-15, a macroreticular
Received November 17, 2008.
Address correspondence to Ajoy K. Banerjee, Centro de Qu ´ı mica, IVIC,
Apartado 21827, Caracas 1020 A, Venezuela. E-mail: abanerje@ivic.ve
3
369

3370
P. S. Poon et al.
[8]
ion-exchange resin; Dowex 50WX2 50–100 mesh, a strongly acidic
[9]
ion-exchange resin; Nafion-H, a polymeric perfluorinated resin sulfonic
[
10]
acid;
and others are notable applications for tetrahydropyranylation
of alcohols. To our knowledge, no one has yet tried tetrahydropyranyla-
tion of alcohols with ion-exchange resin Dowex 50WX4–100. In this
communication, we report for the first time its usefulness in the
protection of alcohols as tetrahydropyranyl ethers.
RESULTS AND DISCUSSION
When a mixture of an alcohol 1 and 3,4-dihydropyran 2 in dry methylene
[
11]
chloride was stirred under nitrogen with a catalytic amount of activated
Dowex 50WX4–100 (see the Experimental Section), corresponding tetra-
hydropyranyl ether 3 was isolated after filtration and chromatography
(Scheme 1).
The experimental procedure is quite simple, and a wide range of alco-
hols (1a–h) including primary, secondary, and cyclic alcohols underwent
smooth tetrahydropyranylation in good yield (Table 1). As can be seen
from Table 1, the Dowex 50WX4–100 efficiently catalyzed the protection
of a variety of alcohols. It is remarkable to observe that the alcohols
(entries 1a–j) underwent protection with 2,4-dihydro-4H-pyran (DHP),
producing corresponding ethers in good yield without undergoing dehy-
dration. Tetrahydropyranylation of alcohols 1i and 1j was accomplished
satisfactorily only after stirring for 24 h with Dowex 50WX4–100 at room
temperature. The sterically hindered alcohols (e.g., triphenylmethanol)
proved resistant to tetrahydropyranylation with this reagent. In addition,
it has been found to be an excellent catalyst for the protection of phenolic
hydroxyl group with DHP in good yield.
In conclusion, we have shown that Dowex 50WX4–100 is an excel-
lent catalyst for the protection of a variety of alcohols. To the best of
our knowledge, some of alcohols selected for tetrahydropyranylation
by Dowex 50WX4–100 were not examined earlier with other catalysts.
We believe that the present method for tetrahydropyranylation would
constitute an important additional approach for the protection of
alcohols with DHP in good yield.
Scheme 1. Tetrahydropyranylation of alcohols catalyzed by Dowex 50WX4-100.

Dowex 50WX4–100
3371
Table 1. Protection of alcohols with DHP (2) catalyzed by Dowex 50WX4–100
Time
Yield (%) (min)
Entry
Alcohol (1)
THP ether (3)
a
97
15
b
c
95
90
10
30
d
e
f
95
98
10
7
Me(CH
2
)
3
OH
94
1
(
Continued )

3372
P. S. Poon et al.
Table 1. Continued
Time
Yield (%) (min)
Entry
Alcohol (1)
THP ether (3)
g
90
88
5
h
15
I
75
1440
J
75
1440
EXPERIMENTAL
Unless otherwise stated, infrared (IR) spectra were taken on a Nicolet
Fourier transform (FT) instrument, and NMR spectra recorded on a
Bruker AM-300 spectrometer in CDCl . Mass spectra (MS) were deter-
3
mined on a Dupont 21–492B. Column chromatography was carried out
on silica gel 60 (Merck). Thin-layer chromatographic (TLC) plates were

Dowex 50WX4–100
3373
coated with silica gel, and the spots were located by exposure to ultravio-
let (UV) light.
Preparation of Activated Ion-Exchange Resin
The Dowex 50WX4–100 (10 g) (Aldrich) was put in a chromatography
column and washed with 2 L hydrochloric acid (6 M HCl). The excess
acid was washed from the column with distilled water until the washings
showed no reaction with silver nitrate, and then it was washed with
ꢀ
methanol. The washed resin was dried in a furnace at 60 C.
Preparation of Alcohols from Ketones
A suspension of sodium borohydride (NaBH ) was added to the commer-
4
cially available ketones (5-methoxy, 7-methoxy a-tetralone, Wieland–
Miescher ketone, benzophenone, and acetophenone) dissolved in ethanol
(analytic grade) and stirred for 1–2 h at room temperature. After acidification
with acetic acid, the product was extracted with dichoromethane, and the
extractwaswashed, driedoverMgSO , and evaporatedtoobtain the alcohols
4
(1a–f). Acetophenone on reduction afforded a mixture of alcohols (1d). The
benzyl alcohol (1e) and n-butano (1f) are commercially available. Tetrahydo-
naphthol (1g) was obtained by catalytic hydrogenation of the a-naphthol.
The alcohol (1h) was prepared by the published procedure. The term Ha
[12]
and H indicate that hydrogen is axial and equatorial respectively.
e
Procedure for Tetrahydropyranylation
A mixture of alcohol (1a–h) (10 mmol), 3,4-dihydropyran 2 (11 mmol),
Dowex 50WX4–100 (0.5 mmol), and dichloromethane (20 ml) was stirred
at room temperature, and the progress of the reaction was monitored by
TLC. After completion, the reaction mixture was filtered off, and the
residue was washed with methylene chloride. The filtrate was concen-
trated, and the residue was purified over a column of silica gel (eluant
hexane–ether 9:1) to obtain the tetrahydropyranyl ethers (3a–j) (Table 1).
Data
Compound 3a
ꢁ
1
IR nmax (cm ): 3069, 2939, 1586, 1471, 1439, 1339, 1255, 1201; MS
þ
þ
þ
2
(
m=z): 262 (M ) (3%), 162 (M ꢁ C H O ) (100%), 85 (C H O)
5
9
5
9

3374
P. S. Poon et al.
1
(
10%), H d(
: 1.58–2.07 (m, 10H), (2 ꢂ CH at C-2, C-3, C-12, C-13,
ppm)
2
C-14), 2.45–2.65 (m, 1H ), 2.70–2.90 (m, 1H ) (CH at C-4), 3.55–3.68
2
e
a
(
(
m, 1H ), 3.97–4.15 (m, 1H ) (CH at C-15), 3.83 (s, 3H, 0Me), 4.73
a e 2
dd, J ¼ 5.6 Hz, J ¼ 4.05 Hz) (1H at C-1), 4.89 (dd, 1H, J ¼ 3.26) (1H at
C-11), 6.77 (dd, 1H, J ¼ 8.09 Hz, J ¼ 1.55 Hz) (1H at C-6), 6.94 (d, 1H,
1
3
J ¼ 7.67 Hz) (1H at C-8), 7.12–7.31 (m, 1H) (1H at C-7); C d(
:
ppm)
1
1
57.17 (C-5), 137.90 (C-9), 126.57 (C-10), 125.78 (C-7), 121.23 (C-8),
08.65 (C-6), 98.84 (C-11), 73.66 (C-1), 62.60 (C-15), 55.23 (C-11), 31.08
(C-13), 30.12 (C-2), 25.60 (C-15), 22.75 (C-4), 19.82 (C-14), 18.17 (C-3).
Compound 3b
ꢁ
1
þ
IR nmax (cm ): 2939, 2868, 1460, 1260, 1233; MS(m=z) 162 (M ꢁ
þ
1
C H O ) , 85 (C H O ); H d
1.42–1.90 (m, 8H) (2 ꢂ CH at C-3,
2
5
9
2
5
9
2
(ppm)
2
C-12, C-13, C-14), 1.92–2.08 (m, 2H) (CH at C-2), 2.56–2.85 (m, 2H)
(CH at C-4), 3.48–3.60 (m, 1H ), 3.90–4.08 (m, 1H ) (CH at C-16),
2 a e 2
3
.77 (s, 3H, OCH ), 4.64 (dd, 1H, J ¼ 1.04 Hz, J ¼ 0.56 Hz) (1H at
3
C-1), 4.81–4.91 (m, 1H) (1H at C-11), 6.75 (dd, 1H, J ¼ 8.35 Hz,
J ¼ 2.76 Hz) (1H at C-6), 6.83 (d, 1H, J ¼ 2.7 Hz) (1H at C-8), 7.01 (d,
1
3
1
H, J ¼ 8.3 Hz) (1H at C-5); C d
: 19.30 (C-13), 19.82 (C-3), 25.50
ppm)
(
(
(
(
C-14), 28.03 (C-4), 30.59 (C-12), 31.07 (C-2), 55.24 (OMe), 62.71
C-15), 74.36 (C-1), 99.29 (C-11), 113.51 (C-6), 113.59 (C-8), 129.70
C-10), 129.86 (C-5), 137.93 (C-9), 157.41 (C-7).
Compound 3c
ꢁ
1
IR nmax (cm ): 30.27, 2941, 290l, 1490, 1452, 1452, 1199, 1120; MS
þ
þ
þ1
(
(
1
m=z): 167 (M ꢁ OTHP) (100%), 184 (M ꢁ THP) (25%), 105 (Ph CO)
2
1
6%); H d
: 1.51–1.62 (m, 4H) (2 ꢂ CH at C-15, C-17), 1.63–1.75 (m,
e
(
ppm)
2
H) (1H at C-16), 1.82–2.05 (m, 1H) (1H at C-16), 3.45–3.56 (m, 1H) (1
a
H at C-18), 3.89 (ddd, 1H, J ¼ 11 Hz, J ¼ 4.5 Hz, J ¼ 3.5 Hz) (1H at
a
e
C-18), 4.62–4.73 (m, 1H) (1H at C-14), 5.81 (s, 1H) (1H at C-1),
7
1
3
.18–7.38 (m, 10H) (aromatic protons); C d(ppm): 19.0 9 (C-16), 25.49
(
(
(
C-17), 30.25 (C-15), 61.91 (C-18), 78.04 (C-1), 95.37 (C-14), 126.76)
C-3, C-7), 126.97 (C-5), 127.51 (C-11), 127.62 (C-9, C-13), 128.11
C-4, C-6), 128.39 (C-10, C-12), 141.69 (C-2), 142.62 (C-8).
Compound 3d
ꢁ1
IR nmax (cm ) 3029, 2934, 2869, 1492, 1448, 1375, 1319, 1282, 1204,
þ
1
1.21, 1076; MS (m=z): 105 (M ꢁ C H O ) (100%), 85 (THP) (55%);
5
9
2

Dowex 50WX4–100
3375
1
0
0
H d(
: 1.37–1.92 (m, 18 H) (9 ꢂ CH at C-8, C-8 , C-10, C-10 , C-11,
ppm)
2
0
0
0
C-11 , C-12, C-12 ), 3.23–3.54 (m, 4H) (2 ꢂ CH at C-13, C-13 ),
2
0
3
.90–4.01 (m, 1H) (C-1 ), 4.32–4.60 (m, 1H) (C-1), 4.75–4.91 (m, 2H)
0
13
(
(
C-9, C-9 ), 7.21–7.42 (m, 10H) (aromatic protons); C d(ppm): 19.22
0 0 0
C-11 ), 19.78 (C-11), 21.90 (C-8, C-8 ), 24.29 (C-12 ), 25.47 (C-12),
0
0
0
3
0.79 (C-10, C-10 ), 61.79 (C-13 ), 62.67 (C-13), 73.01 (C-1 ), 73.17
0
0
0
(
1
C-1), 96.03 (C-9), 96.17 (C-9 ), 125.95 (C-4 , C-6 ), 126.37 (C-4, C-6),
0
0
0
26.90 (C-5 ), 127.32 (C-5), 128.12 (C-3 , C-7 ), 128.33 (C-3, C-7), 143
0
(
C-2), 144.47 (C-2 ).
Compound 3e
ꢁ
1
IR nmax (cm ): 3063, 3031, 2942, 2870, 1496, 1454, 1261, 1078; MS
þ
þ
þ
1
(
m=z): 85 (M ꢁ PhCH O) (100%), 108 (M ꢁ C H O) (8%);
H
2
5
9
d
1
4
1
d
: 1.50–1.92 (m, 6H) (3 ꢂ CH at C-10, C-9, C-11), 3.50–3.62 (m,
(
ppm)
2
H ) (C-12), 3.95 (ddd, 1H , J ¼ 11 Hz, J ¼ 3.38 Hz, J ¼ 3.50) (C-12),
a
e
.50 (d, 1H , J ¼ 12.03 Hz) (C-1), 4.71 (t, 1H, J ¼ 4 Hz) (C-8), 4.79 (d,
a
1
3
H , J ¼ 12.24 Hz) (C-1), 7.25–7.45 (m, 5H) (aromatic protons);
C
e
: 19.31 (C-10), 25.45 (C-11), 30.54 (C-9), 62.05 (C-12), 68.76
ppm)
(
(
1
C-1), 97.68 (C-8), 127.44 (C-5), 127.75 (C-3, C-7), 128.31 (C-4, C-6),
38.28 (C-2).
Compound 3f
ꢁ
1
þ
IR nmax (cm ): 2963, 2868, 1440, 1199, 1076; MS (m=z): 101 (M ꢁ
þ
1
C H ) (100%) (57 (M ꢁ C H O (25%); H d
: 1.20–1.91 (m, 13H)
(ppm)
4
9
5
9
2
(
(
(
CH at C-1) (6 ꢂ CH at C-2, C-3, C-6, C-7, C-8), 3.20–3.52 (m, 2H)
3
2
CH at C-4), 3.50–4.01 (m, 2H) (CH at C-9), 4.65–4.70 (m, 1H )
2 2 a
1
3
C-5), 4.75–4.82 (m, 1H ) (C-5); C d(ppm): 19.49 (C-1), 19.57 (C-2),
e
2
(
5.17 (C-7), 25.28 (C-8), 30.46 (C-6), 30.75 (C-3), 62.56 (C-9), 63.05
C-1), 98.28 (C-5 ), 94.23 (C-5 ).
a
e
Compound 3g
ꢁ
1
þ
IR nmax (cm ): 3029, 2933, 2857, 1462, 1333, 1247; MS (m=z): 232 (M )
þ
þ1
þ
1
(
d
25%), 148 (M ꢁ C H O)
(100%), 85 (M ꢁ C H O) (51%);
10 11
H
5
9
: 1.51–1.90 (m, 9H) (4 ꢂ CH 1H) (C-13, C-14, C-6, C-7, C-12–
2 Ha
(
ppm)
2
1Ha), 2.58–2.78 (m, 4H) (2 ꢂ CH at C-5, C-8), 3.55–3.63 (m, 1
)
C-15), 3.85–3.97 (m, 1He) (C-15), 5.39–5.41 (m, 1Ha) (C-11), 6.71 (d,
(
1
H, J ¼ 8 Hz) (C-4), 6.88 (d, 1H, J ¼ 7 Hz) (C-2), 7.02 (dd, 1H, J ¼ 8 Hz,
1
3
J ¼ 7 Hz); C d(
: 18.95 (C-13), 22.87 (C-6, C-7), 23.25 (C-8), 25.34
ppm)

3376
P. S. Poon et al.
(
1
C-14), 29.66 (C-5), 30.62 (C-12), 61.94 (C-15), 95.89 (C-11), 110.75 (C-2),
22.17 (C-4), 125.65 (C-3), 126.59 (C-9), 138.50 (C-10), 154.65 (C-4).
Compound 3h
ꢁ
1
þ þ1
IR nmax (cm ): 2941, 2856, 1671 (CO), 1447, 1350; MS (m=z): 264 (M )
þ
þ1
1
(
20%), 180 (M ꢁ 85) , (100%); H d
: 1.20–2.01 (m, 12H) (2 ꢂ CH
(
ppm)
2
at C-13, C-14, C-15, C-2, C-3, C-4), 3.34–3.46 (m, 2H) (C-16), 3.79–3.90
1
3
(
m, 1H) (C-1), 4.52–4.56 (m, 1H) (C-12), 5.72 (s, 1H) (C-5); C d(ppm)
8.96 (C-19), 22.89 (C-14), 29.07 (C-3), 30.64 (C-15), 31.96 (C-2), 32.13
C-13), 33.76 (C-4), 34.36 (C-8), 34.57 (C-7), 43.56 (C-9), 66.39 (C-16),
6.70 (C-1), 98.83 (C-12), 125.17 (C-5), 168.64 (C-12), 199.63 (C-6).
:
1
(
8
Compound 3i
þ
þ
þ
9
1
MS (m=z): 168 (M ꢁ C H ), 111 (M ꢁ C H -NO-CO), 85 (C H O ); H
4
7
4
6
5
d
: 1.40–1.93 (m, 6H, CH at C-8, C-9, C-10), 3.38–3.53 (m, 2H) (C-11),
2
(ppm)
5
.42 (t, 1H, J ¼ 3.1 Hz) (C-7), 7.29 (ddd, 1H, J ¼ 7.8Hz, J ¼ 2.3 Hz,
J¼ 1.6 Hz) (C-6), 7.34 (ddd, 1H, J ¼ 7.8 Hz, J ¼ 7.8 Hz, J ¼ 0.5 Hz) (C-5),
.73 (ddd, 1H, J ¼ 7.8 Hz, J ¼ 2.3 Hz, J ¼ 1.6 Hz) (C-4), 7.83 (ddd, 1H,
7
13
J¼ 2.3 Hz, J¼ 2.3 Hz, J¼ 0.5 Hz) (C-2); C d(
: 18.31 (C-9), 24.89
ppm)
(C-10), 30.06 (C-8), 61.89 (C-11), 98.35 (C-7), 111.30 (C-2), 116.23 (C-4),
122.72 (C-6), 129.70 (C-5), 149.03 (C-3), 157.46 (C-1).
Compound 3j
MS (m=z): 168 (M ꢁ C H ), 85 (C H O ); H d(ppm): 1.36–1.70 (m, 6H,
þ
þ
9
1
4
7
5
CH at C-8, C-9, C-10), 3.31–3.34 (m, 2H) (C-11), 5.36 (t, 1H, J ¼ 3.0 Hz)
2
(
C-7), 6.94 (d, 2H, J ¼ 9.3 Hz) (C-6, C-2), 7.98 (d, 2H, J¼ 9.3 Hz) (C-5,
1
3
C-3); C d(
: 18.06 (C-9), 24.74 (C-10), 30.74 (C-8), 61.72 (C-11), 96.17
ppm)
(C-7), 116.01 (C-2, C-6), 125.37 (C-3, C-5), 141.69 (C-4), 161.97 (C-1).
ACKNOWLEDGMENT
The partial economic support from Ley Organica de Ciencia, Tecnologia
e Innovacion (LOCTI) is gratefully acknowledged.
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Dowex 50WX4–100
3377
2
3
4
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7
. Gelbard, G. Organic synthesis by catalysis with ion-exchange resins. Ind. Eng.
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8
. Bongini, A.; Cardillo, G.; Orena, M.; Sandri, S. A simple and practical
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9
. Nishiguchi, T.; Kuroda, M.; Saitoh, M.; Nishida, A.; Fujisaki, S. Highly
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