Tetrahydropyranylation of alcohols and phenols catalyzed by a new polystyrene-bound tin(IV) porphyrin

Article abstract of DOI:10.1016/j.molcata.2011.01.023

In the present work, tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) catalyzed by tetrakis(p-aminophenyl) porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH ₂PP)(OTf)₂], supported on chloromethylated polystyrene is reported. The prepared catalyst was characterized by elemental analysis, FT-IR and diffuses reflectance UV-Vis spectroscopic methods. This new heterogenized catalyst was found as efficient and reusable catalyst for tetrahydropyranylation of primary, secondary and tertiary alcohols as well as phenols at room temperature.

Full text of DOI:10.1016/j.molcata.2011.01.023

Journal of Molecular Catalysis A: Chemical 337 (2011) 95–101
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Tetrahydropyranylation of alcohols and phenols catalyzed by a new
polystyrene-bound tin(IV) porphyrin
Majid Moghadama,b,∗, Shahram Tangestaninejada,∗∗, Valiollah Mirkhania,
Iraj Mohammadpoor-Baltorka, Shadab Gharaatia
a Department of Chemistry, Catalysis Division, University of Isfahan, Hezar Jerib, Isfahan 81746-73441, Iran
b Department of Nanotechnology Engineering, University of Isfahan, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present work, tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-
pyran (DHP) catalyzed by tetrakis(p-aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate,
[SnIV(TNH2PP)(OTf)2], supported on chloromethylated polystyrene is reported. The prepared catalyst
was characterized by elemental analysis, FT-IR and diffuses reflectance UV–Vis spectroscopic methods.
This new heterogenized catalyst was found as efficient and reusable catalyst for tetrahydropyranylation
of primary, secondary and tertiary alcohols as well as phenols at room temperature.
© 2011 Elsevier B.V. All rights reserved.
Received 17 October 2010
Received in revised form 20 January 2011
Accepted 22 January 2011
Available online 28 January 2011
Keywords:
Hydroxy compound
Supported catalyst
Tin(IV) porphyrin
Electron deficient
THP ether
1. Introduction
mations in a synthetic sequence, especially in the synthesis of fine
chemicals and natural products. Amongst them, tetrahydropyrany-
There is an increasing demand in catalysis for developing
systems that allow the recovery and reuse of the catalyst. Envi-
ronmental concerns together with economic considerations make
necessary and convenient this recovery [1–3]. Since transition-
metal complexes are often expensive to purchase or prepare, their
immobilization on a support offer a several advantages over their
homogeneous counterparts. Supported catalysts can be recovered
from reaction mixtures by simple filtration, they do not contam-
inate the product solution, they can be recycled, and they can
increase selectivity [4].
Polystyrene is one of the most popular polymeric supports used
in synthetic organic chemistry because of its inexpense, ready
availability, mechanical robustness, chemical inertness, and facile
functionalization.
The importance of selective introduction and removal of pro-
tecting groups in organic synthesis is well established. These
protections are necessary during the course of various transfor-
lation is one of the most frequently used methods for the protection
of hydroxyl groups in synthetic organic chemistry, in particular
natural product chemistry, because of its easy installation, general
stability to most nonacidic reagents, and easy removal under mild
acidic conditions [5,6].
A variety of catalysts including protonic and Lewis acid catalysts
such as p-toluene sulfonic acid (PTSA) [7], bis[trimethylsilyl]sulfate
[8], (CH3)3SiI [9], CuCl2 [10], DDQ [11], Ru(CH3)3(triphos)](OTf)2
[12], I2 [13], AlCl3·6H2O [14], In(OTf)3 [15], ZrCl4 [16],
K5CoW12O40·3H2O [17], ionic liquids [18], Bu4N+Br3
[19],
−
and LiOTf [20], K-10 clay [21], alumina impregnated with
ZnCl2 [22], silica chloride [23], AlCl3@PS [24], silica-based
sulfonic acid [25,26], H6P2W18O62 [27], PdCl2(CH3CN)2 [28],
vanadyl(IV) acetate [29] and [SnIV(TPP)(OTf)2] [30] have
been developed for tetrahydropyranylation of alcohols and
phenols.
Although these procedures provide an improvement, many of
these catalysts or activators need long reaction times, drastic reac-
tion conditions or tedious workups, moisture sensitive or expensive
of the catalyst. Hence, introduction of new procedures to circum-
vent these problems is still in demand.
Electron-deficient metalloporphyrins have been used as mild
Lewis acids catalysts [31–34]. Suda group has reported the
use of chromium and iron porphyrins in organic synthesis.
They used Cr(tpp)Cl for regioselective [3,3] rearrangement of
∗
Corresponding author at: Department of Chemistry, Catalysis Division, Univer-
sity of Isfahan, Hezar Jerib, Isfahan 81746-73441, Iran.
Tel.: +98 311 7932712; fax: +98 311 6689732.
∗∗
Corresponding author. Tel.: +98 311 7932712; fax: +98 311 6689732.
E-mail addresses: moghadamm@sci.ui.ac.ir, majidmoghadamz@yahoo.com
(M. Moghadam), stanges@sci.ui.ac.ir (S. Tangestaninejad).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.01.023

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M. Moghadam et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 95–101
[SnIV(TNH2PP)(OTf)2@CMP]
R
OH
+
THF
O
RO
O
Scheme 1. Tetrahydropyranylation of alcohols and phenols with DHP catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP.
aliphatic allyl vinyl ethers and for Claisen rearrangement of sim-
ple aliphatic allyl vinyl ethers, Fe(tpp)OTf for rearrangement of
␣,␤-epoxy ketones into 1,2-diketones and Cr(tpp)OTf for highly
regio- and stereoselective rearrangement of epoxides to aldehydes
[35–38].
Recently, we have reported the use of tetraphenylporphyri-
natotin(IV) perchlorate [39,40], tetraphenylporphyrinatotin(IV)
trifluoromethanesulfonate [30,41–44], and tetraphenylporphyri-
natotin(IV) tetraflouroborate [45–47] in organic transforma-
tions.
In the present work, preparation, characterization and inves-
tigation of catalytic activity of tetrakis(p-aminophenyl)porphyrin-
atotin(IV) trifluoromethanesulfonate, [SnIV(TNH2PP)(OTf)2], sup-
ported on chloromethylated polystyrene in the tetrahydropy-
ranylation of alcohols and phenols with 3,4-dihydro-2H-pyran is
reported (Scheme 1).
Scheme 2. The preparation route for [SnIV(TNH2PP)(OTf)2]@CMP.

M. Moghadam et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 95–101
97
2. Experimental
2.3. General procedure for tetrahydropyranylation of alcohol and
phenols catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP
Chemicals were purchased from Merck or Fluka chemical
companies. Chloromethylated polystyrene (cross-linked with
2% divinylbenzene, 4–5% Cl content, 1.14–1.40 mmol/g Cl) was
purchased from Fluka. FT-IR spectra were obtained with potas-
sium bromide pellets in the range 400–4000 cm−1 with a Nicolet
Impact 400D spectrometer. Gas chromatography experiments
A
mixture
of
alcohol
or
phenol
(1 mmol),
[SnIV(TNH2PP)(OTf)2]@CMP (70 mg, 0.01 mmol) and DHP (2 mmol
per OH group) in THF (0.5 mL) was prepared and stirred at room
temperature for appropriate time. The progress of the reaction
was monitored by GC. After completion of the reaction, Et2O
(10 mL) was added and the catalyst was filtered. The filtrates were
concentrated under reduced pressure to afford the crude product.
(GC) were performed with
a Shimadzu GC-16A instrument
using a 2 m column packed with silicon DC-200 or Carbowax
20 m. In the GC experiments, n-decane was used as an internal
standard. 1H NMR spectra were recorded on a Bruker-Avance
AQS 400 MHz spectrometer. Tetra(4-aminophenyl)porphyrin
was prepared and metallated according to the literature
[48,49].
2.4. Catalyst reusability
At the end of each reaction, the catalyst was filtered, washed
thoroughly with Et2O, dried and reused.
3. Results and discussion
2.1. Supporting of [SnIV(TNH2PP)Cl2] on chloromethylated
polystyrene, [SnIV(TNH2PP)Cl2]@CMP
3.1. Preparation and characterization of
[SnIV(TNH2PP)(OTf)2]@CMP
To a solution of [SnIV(TNH2PP)Cl2] (0.5 g) in DMF (50 mL),
were added chloromethylated polystyrene (2.5 g) and tri-
ethylamine (3 mL). The mixture was heated at 100 ◦C
for 72 h. After cooling to room temperature, the green
solids were filtered, washed with ethanol and acetone and
dried.
Scheme
2
shows
the
preparation
route
for
[SnIV(TNH2PP)(OTf)2]@CMP. First, chloromethylated polystyrene
(cross-linked with 2% divinylbenzene, 4–5% Cl content,
1.14–1.40 mmol/g Cl) was reacted with [SnIV(TNH2PP)Cl2] to
obtain the [SnIV(TNH2PP)Cl2]@CMP. Then, the chlorines were
substituted by OTf− by the reaction of [SnIV(TNH2PP)Cl2]@CMP
with NaOTf. This increases the electron deficiency of tin(IV).
The prepared catalyst was characterized by elemental analysis,
FT IR and UV–Vis spectroscopic methods. The nitrogen con-
tent of the catalyst was measured to be 1.64% (1.17 mmol/g).
According to this value, the amount of porphyrin introduced to
polystyrene was calculated as 0.146 mmol/g. The evidence for
attachment of tin(IV) porphyrin on the polystyrene was obtained
2.2. Conversion of [SnIV(TNH2PP)
Cl2]@CMP to [SnIV(TNH2PP)(OTf)2]@CMP
To a suspension of [SnIV(TNH2PP)Cl2]@CMP (2 g) in THF (50 mL)
was added NaOTf (1 g) and stirred at 60 ◦C for 8 h. After, the catalyst
was filtered and washed with ethanol.
Fig. 1. The FT IR spectrum of (A) chloromethylated polystyrene; (B) [SnIV(TNH2PP)Cl2]; (C) [SnIV(TNH2PP)Cl2]@CMP and (D) [SnIV(TNH2PP)(OTf)2]@CMP.

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M. Moghadam et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 95–101
Table 1
Optimization of catalyst amount in the acetylation of 4-chlorobenzyl alcohol with DHP catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP.
Entry
Time (min)
Catalyst amounts (mmol, mg)
DHP (mmol)
Solvent
Yield (%)a
1
2
3
4
5
6
7
8
9
6
6
6
6
6
6
6
6
6
6
6
40 mg (0.006 mmol)
50 mg (0.0071 mmol)
60 mg (0.0086 mmol)
70 mg (0.010 mmol)
80 mg (0.011 mmol)
70 mg (0.010 mmol)
70 mg (0.010 mmol)
70 mg (0.010 mmol)
70 mg (0.010 mmol)
70 mg (0.010 mmol)
70 mg (0.010 mmol)
2
2
2
2
2
2
2
2
THF
THF
THF
THF
22
61
84
100
100
88
58
44
17
51
THF
CH3CN
CH2Cl2
CHCl3
n-Hexane
THF
2
1
1.5
10
11
THF
76
a
GC yield.
from FT IR spectra of chloromethylated polystyrene (Fig. 1A),
[SnIV(TNH2PP)Cl2] (Fig. 1B), [SnIV(TNH2PP)Cl2]@CMP (Fig. 1C) and
[SnIV(TNH2PP)(OTf)2]@CMP (Fig. 1D). The bands at 2920 cm−1
and 2850 cm−1 in the FT-IR spectrum of [SnIV(TNH2PP)Cl2]@CMP
and the bands at 2919 cm−1 and 2850 cm−1 in the FT-IR spec-
tra of [SnIV(TNH2PP)(OTf)2]@CMP are attributed to stretching
vibrations of aliphatic C–H bond. These bands which do not
present in the homogeneous [SnIV(TNH2PP)Cl2] are an indi-
cation for attachment of porphyrin on the polystyrene. The
presence of the band at 1724 cm−1 in the FT-IR spectrum of
[SnIV(TNH2PP)Cl2]@CMP and 1725 cm−1 in the FT-IR spectrum of
[SnIV(TNH2PP)(OTf)2]@CMP are attributed to bending vibrations
of N–H secondary amine which does not present in the FT-IR
spectrum of the [SnIV(TNH2PP)Cl2].An indication for conversion
of [SnIV(TNH2PP)Cl2]@CMP to [SnIV(TNH2PP)(OTf)2]@CMP is the
appearance of bands at 1284 cm−1 and 1173 cm−1 that are related
to stretching vibrations of C–F and S O bonds, respectively.
The bands at 3493 cm−1 and 3429 cm−1 in FT-IR spectrum
of the [SnIV(TNH2PP)Cl2]@CMP and the bands at 3421 cm−1 and
3350 cm−1 of in FT-IR spectrum of the [SnIV(TNH2PP)(OTf)2]@CMP
are attributed to stretching vibrations of N–H primary and sec-
ondary amines. The bands at 1678 cm−1 in the FT-IR spectrum of
the [SnIV(TNH2PP)Cl2]@CMP and 1679 cm−1 in the FT-IR spectrum
of [SnIV(TNH2PP)(OTf)2]@CMP are attributed to bending vibrations
of N–H primary amine. Since these bands do not present in the
chloromethylated polystyrene, it is clear that the porphyrin has
been attached to polystyrene. The sharp C–Cl peak (due to –CH2Cl
groups) at 1264 cm−1 in the starting polymer was practically omit-
ted or seen as a weak band after introducing of tin(IV) porphyrin
on the polymer.
results clearly indicated that the presence of OTf groups is necessary
for having a good catalytic activity.
Under the optimized conditions, different alcohols were sub-
jected to tetrahydropyranylation with DHP in the presence of
[SnIV(TNH2PP)Cl2]@CMP at room temperature (Table 2). The results
showed that primary, secondary and tertiary alcohols including
aromatic, aliphatic and cyclic ones were converted efficiently to
their corresponding tetrahydropyranyl ethers in excellent yield. In
the case of aromatic alcohols, the nature of substituents has no
significant effect on the tetrahydropyranylation yield.
The ability of [SnIV(TNH2PP)Cl2]@CMP/DHP catalytic system
was also investigated in the tetrahydropyranylation of phenols
The homogeneous [SnIV(TNH2PP)(OTf)2] showed absorption
peaks at 430 (Soret band), 562 and 620 (Q bands) nm (Fig. 2A).
The reflectance of the polymer-bound porphyrin resembles solu-
tion counterpart spectrum with only a slight shift and a Soret
band at 435 nm and Q bands at 560 and 619 nm, which clearly
indicates the presence of metalloporphyrin on the polystyrene
(Fig. 2B).
3.2. Tetrahydropyranylation of alcohols and phenols catalyzed by
[SnIV(TNH2PP)(OTf)2]@CMP
First, the reaction parameters such as amount of catalyst,
kind of solvent and amount of DHP were optimized in the
tetrahydropyranylation of 4-chlorobenzyl alcohol. The results,
which are summarized in Table 1, showed that the highest
yield of THP-ether was obtained in the presence of 1 mol%
(70 mg) of [SnIV(TNH2PP)(OTf)2]@CMP with 2 mmol of DHP
in THF as solvent (Table 1). Then, the catalytic activity of
[SnIV(TNH2PP)Cl2]@CMP was also investigated in the tetrahy-
dropyranylation of 4-chlorobenzyl alcohol, The results showed that
only 21% of the corresponding THP-ether was produced. These
Fig. 2. The UV–Vis spectrum of (A) homogeneous [SnIV(TNH2PP)(OTf)2] and (B)
heterogeneous [SnIV(TNH2PP)(OTf)2]@CMP.

M. Moghadam et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 95–101
99
Table 2
Tetrahydropyranylation of alcohols catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP at room temperature.a
Entry
Hydroxy compound
THP ether
Time (min)
4
Yield (%)b
CH2OH
CH2OTHP
CH2CH2OTHP
CH2CH2CH2OTHP
CH2OTHP
1
97
95
96
99
62
95
CH2CH2OH
2
3
4
5
6
3
3
6
6
4
CH2CH2CH2OH
CH2OH
Cl
Cl
O2N
MeO
CH2OH
O2N
MeO
CH2OTHP
CH2OTHP
CH2OH
CH2OH
CH2OTHP
8
9
4
4
95
94
OMe
CH2OH
OMe
CH2OTHP
Me
Me
OH
OTHP
10
11
4
4
93
90
OH
OTHP
OH
OTHP
12
4
96
OH
OTHP
13
14
6
6
94
96
CH3
CH3
H3C C CH3
H3C
C
CH3
OH
OTHP
OH
OTHP
15
6
93
e
a
Reaction conditions: alcohol (1 mmol), DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL).
Isolated yield.
b
Recently, we reported the use of homogeneous [SnIV(TPP)
(OTf)2] in the tetrahydropyranylation of alcohols and phenols [30].
The reaction times in the presence of 1 mol% of the homogeneous
catalyst were 3–6 min and the product yields were 60–97%. In com-
parison with its homogeneous counterpart [30], in the presence
of 1 mol% of [SnIV(TNH2PP)(OTf)2]@CMP, the corresponding THP-
ethers were obtained in 63–99% in 3–6 min. These observations
showed that [SnIV(TNH2PP)(OTf)2]@CMP, which is a heterogeneous
catalyst, has reserved its catalytic activity. On the other hand, the
reusability of this catalyst was higher and can be separated by sim-
ple filtration in which does not contaminate the reaction product.
under the same reaction conditions described for alcohols and the
corresponding THP-ethers were obtained in high yields and short
reaction times (Table 3).
Since this catalytic system was active in the tetrahydropyranyla-
tion of primary, secondary and tertiary alcohols and also phenols,
we decided to investigate the chemoselectivity of the presented
method. In this manner, a set of competitive reactions was con-
ducted between primary or secondary and tertiary alcohols or
phenols (Table 4). The results indicated that primary alcohols are
more reactive in the presence of secondary and tertiary alcohols
and phenols.

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M. Moghadam et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 95–101
Table 3
Tetrahydropyranylation of phenols with DHP catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP at room temperature.a
Entry
1
Phenol
THP ether
Time (min)
5
Yield (%)b
91
OTHP
OH
Cl
OTHP
Cl
OH
2
3
4
5
5
5
91
67
91
O2N
H3C
OH
O2N
H3C
OTHP
OTHP
OH
OTHP
OH
5
5
90
a
Reaction conditions: phenol (1 mmol), DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL).
Isolated yield.
b
3.3. Catalyst reuse and stability
alyst was consecutively reused seven times without a detectable
catalyst leaching or a significant loss of its activity (Table 5). After
each run the filtrates were used for determination of catalyst leach-
ing. No Sn was detected in the filtrates by ICP. Also, the catalytic
behavior of the separated liquid was tested by addition of fresh
4-chlorobrnzyl alcohol and DHP to the filtrates after each run.
Execution of the acetylation reaction under the same reaction con-
ditions, as with catalyst, showed that the obtained results were as
The stability of the [SnIV(TNH2PP)(OTf)2]@CMP catalyst was
monitored using multiple sequential tetrahydropyranylation of
4-chlorobenzyl alcohol with DHP. For each of the repeated reac-
tions, the catalyst was filtered, washed exhaustively with water,
ethanol, acetonitrile and diethyl ether, respectively, and dried
before using with fresh 4-chlorobrnzyl alcohol and DHP. The cat-
Table 4
Selective tetrahydropyranylation of alcohols and phenols catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP.a
Row
1
ROH
THP ether
Time (min)
4
Yield (%)b
85
CH2OH
OH
CH2OTHP
OTHP
21
90
2
4
CH2OH
CH2OTHP
Me
Me
OH
Me
Me
23
95
OTHP
3
4
4
CH2OTHP
CH2OH
OH
OTHP
45
92
4
CH2OTHP
OTHP
CH2OH
OH
7
a
Reaction conditions for a binary mixture: 1 mmol of each alcohol or phenol, DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL).
GC yield.
b

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101
Table 5
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100
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6
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0
0
0
0
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a
Reaction conditions: 4-chlorobenzyl alcohol (1 mmol), DHP (2 mmol), catalyst
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GC yield.
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32 (2002) 1337–1343.
Fig. 3. The DR UV–Vis spectrum of recovered [SnIV(TNH2PP)(OTf)2]@CMP.
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same as blank experiments. The nature of recovered catalyst was
monitored by diffuse reflectance UV–Vis spectrophotometry. No
change was observed in the DR UV–Vis spectrum of the catalyst
which indicates the stability and robustness of the catalyst (Fig. 3).
4. Conclusion
In conclusion, a new, robust, stable and heterogeneous tin(IV)
compound was prepared, characterized for the first time. This new
electron deficient tin(IV) porphyrin, [SnIV(TNH2PP)(OTf)2]@CMP,
was used for efficient tetrahydropyranylation of primary, sec-
ondary and tertiary alcohols and phenols with DHP. Short reaction
times, excellent yields, easy work-up and reusability and stability
of the catalyst are noteworthy advantages of this method.
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